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Williams Obstetrics, 25th Ed

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illiams
OBSTETRICS
25TH EDITION
F. Gary Cunningham
Kenneth J. Leveno
Steven L. Bloom
Jodi S. Dashe
Barbara L. Hofman
Brian M. Casey
Catherine Y. Spong
New York
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Williams Obstetrics, Twenty-Fih Edition
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Copyright © 2014 by McGraw-Hill Education.
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Copyright © 1985 by Appleton-Century-Crofts
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Copyright © 1946,1941,1936 by D. Appleton-Centuy-Co.,Inc.
Copyright © 1930,1923,1917,1912,1909.1907,1904,1903.1902 by D. Appleton and Company
Copyright © 1964 by Florence C. Stander
Copyright © 1951 by Anne W. Niles
Copyright © 1935. 1940 by Caroline W. Williams
Copyright © 1930. 1931. 1932 by]. Whitridge Williams
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EDITORS
F. Gary C u n n i n g ham, MD
Beatrice & Miguel Elias Distinguished Chair i n Obstetrics and
Gynecology
Barbara L. Hoffma n, MD
Professor, Department o f Obstetrics and Gynecology
University of Texas Southwestern Medical Center
Professor, Department of Obstetrics and Gynecology
Parkland Health and Hospital System
University of Texas Southwestern Medical Center
Dallas, Texas
Parkland Health and Hospital System
Dallas, Texas
Brian M. Casey, MD
Professor, Department of Obstetrics and Gynecology
Ken neth J. Leveno, MD
Director, Division of Maternal-Fetal Medicine
Professor, Department o f Obstetrics and Gynecology
University of Texas Southwestern Medical Center
University of Texas Southwestern Medical Center
Chief of Obstetrics
Parkland Health and Hospital System
Parkland Health and Hospital System
Dallas, Texas
Dallas, Texas
Steven L. Bloom, MD
Catherine Y. Spong, M D
Jack A . Pritchard M D Chair i n Obstetrics and Gynecology
Bethesda, Maryland
Professor and Chair, Department of Obstetrics and Gynecology
University of Texas Southwesten Medical Center
Chief of Obstetrics and Gynecology
Parkland Health and Hospital System
Dallas, Texas
Jodi S. Das he, MD
Professor, Department o f Obstetrics and Gynecology
University of Texas Southwestern Medical Center
Director of Prenatal Diagnosis
Parkland Health and Hospital System
Dallas, Texas
v
ASSOCIATE E DITORS
Mala S. Mahendroo, PhD
J. Seth Hawki ns, MD, MBA
Associate Professor, Department o f Obstetrics and Gynecology and
Assistant Professor, Department of Obstetrics and Gynecology
Green Center for Reproductive Biological Sciences
University of Texas Southwestern Medical Center
University of Texas Southwestern Medical Center
Parkland Health and Hospital System
Dallas, Texas
Dallas, Texas
Diane M. Twickler, M D, FACR
Dr. Fred Bonte Professorship in Radiology
Professor, Department of Radiology and Obstetrics and Gynecology
Vice Chairman for Academic Affairs, Department of Radiology
University of Texas Southwestern Medical Center
Medical Director of Obstetrics and Gynecology Ultrasonography
Parkland Health and Hospital System
Dallas, Texas
CONTRIBUTING E DITORS
Apri l A. Ba i l ey, M D
Weike Tao, MD
Assistant Professor, Department of Radiology and Obstetrics and
Associate Professor, Department o f Anesthesiology and Pain
Gynecology
University of Texas Southwestern Medical Center
Parkland Health and Hospital System
Parkland Health and Hospital System
Dallas, Texas
Dallas, Texas
Donald D. Mcinti re, PhD
C. Edward Wel ls, MD
Biostatistician
Professor, Department of Obstetrics and Gynecology
Professor, Department of Obstetrics and Gynecology
University of Texas Southwestern Medical Center
University of Texas Southwestern Medical Center
Parkland Health and Hospital System
Dallas, Texas
Dallas, Texas
David B. Nelson, MD
Myra H. Wyckoff, MD
Dedman Family Scholar i n Clinical Care
Professor, Department of Pediatrics
Assistant Professor, Department of Obstetrics and Gynecology
University of Texas Southwestern Medical Center
University of Texas Southwestern Medical Center
Director, Newborn Resuscitation Services
Medical Director of Prenatal Clinics
Parkland Health and Hospital System
Parkland Health and Hospital System
Dallas, Texas
Dallas, Texas
Jeanne S. Sheffield, MD
Professor, Department o f Obstetrics and Gynecology
Director, Division of Maternal-Fetal Medicine
Johns Hopkins University School of Medicine
Baltimore, Maryland
vi
Management
University of Texas Southwestern Medical Center
DEDICATION
To our mentors, who inspire us to strive for excellence in obstetrics,
To our colleagues, who are superb role models for obstetricians and gynecologists,
To our students and residents, who challenge us to be better teachers each day,
To our fellows, who dare us to think more boldly,
To our nurses, who encourage us to place patient needs first,
To our support staf, who allow us to respond eiciently in the face of emergencies, and
To our families, whose love and support make our endeavors possible.
vii
CONTENTS
Preface
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xiii
Acknowledgments. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
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OVERVIEW
1. Overview of Obstetrics.................... 2
MATERNAL ANATOMY AND PHYSIOLOGY
2. Maternal Anatomy
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4. Maternal Physiology
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3. Congenital Genitourinary
Abnormalities
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PLACENTATION, EMBRYOGENESIS, AND FETAL DEVELOPMENT
5. Implantation and Placental
Development
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6. Placental Abnormalities
7. Embryogenesis and Fetal
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Development
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Conte nts
PRECONCEPTIONAL AND PRENATAL CARE
8. Preconceptional Care
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9. Prenatal Care
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THE FETAL PATIENT
10. Fetal Imaging. . . . . . . . . . . . . . . . . . . . . . . . . . . 182
14. Prenatal Diagnosis
11. Amnionic Fluid ..
15. Fetal Disorders ..... ......... ....
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16. Fetal Therapy. . . . . . . . . . . . . . . . . . . . . . . . . . . 315
12. Teratology, Teratogens, and
Fetotoxic Agents
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17. FetaI Assessment . . . . . . . . . . . . . . . . . . . . . . 331
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13. Genetics
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EARLY PREGNANCY COMPLICATIONS
18. Abortion
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19. Ectopic Pregnancy .
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20. Gestational Trophoblastic Disease
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LABOR
21. Physiology of Labor
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22. Normal Labor.
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23. Abnormal Labor
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24. Intrapartum Assessment
25. Obstetrical Analgesia and
Anesthesia . .. . . . . . . . . . . . . . . . . . . . . . . . . . . 485
26. Induction and Augmentation
of Labor
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Co ntents
DELIVERY
27. Vaginal Delivery ........................516
28. Breech Delivery .........................539
29. Operative Vaginal Delivery ..............553
30. Cesarean Delivery and Peripartum
Hysterectomy ..........................567
31. Prior Cesarean Delivery .................591
THE NEWBORN
32. The Newborn. . . . . . . . . . . . . . . . . . . . . . . . . . . 606
34. The Preterm Newborn
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33. Diseases and Injuries of
35. Stillbirth
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the Term Newborn .....................619
THE PUERPERIUM
36. The Puerperium ........................652
38. Contraception .
37. Puerperal Complications . . . . . . . . . . . . . . . . 666
39. Sterilization............................ .702
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OBSTETRICAL COMPLICATIONS
40. Hypertensive Disorders .................710
43. Postterm Pregnancy . . . . . . . . . . . . . . . . . . . . 835
41. Obstetrical Hemorrhage
44. Fetal-Growth Disorders .
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42. Preterm Birth . . . . . . . . . . . . . . . . . . . . . . . . . . . 803
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844
45. Multifetal Pregnancy. . . . . . . . . . . . . . . . . . . . 863
xi
xii
Contents
MEDICAL AND SURGICAL COMPLICATIONS
46. General Considerations and
56. Hematological Disorders.............. 1075
Maternal Evaluation ....................900
47. Critical Care and Trauma ................915
48. Obesity.................................936
49. Cardiovascular Disorders................948
50. Chronic Hypertension...................975
51. Pulmonary Disorders....................987
52. Thromboembolic Disorders ........... 1004
53. Renal and Urinary Tract Disorders ..... 1025
54. Gastrointestinal Disorders............. 1042
57. Diabetes Mellitus ..................... 1097
58. Endocrine Disorders .................. 1118
59. Connective Tissue Disorders
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60. Neurological Disorders................ 1156
61. Psychiatric Disorders.................. 1173
62. Dermatological Disorders ............. 1184
63. Neoplastic Disorders.................. 1190
64. Infectious Diseases ................... 1209
65. Sexually Transmitted Infections ... . 1235
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55. Hepatic, Biliary, and Pancreatic
Disorders ............................. 1058
Serum and BI 00 d C0 nst·ltuents ........... 1255
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Fetal Sonographic Measurements ......... 1262
Maternal Echocardiographic
Mea surements....................... 1261
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Index
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1273
PREFACE
We celebrate this 25th edition of Wiliams Obstetrics with great
appreciation for the insight and expertise that the early editors
brought to this textbook. To pay tribute to the irst author, J .
Whitridge Williams, we begin each chapter with a passage from
his 1 st edition that complements the topic. During this selec­
tion process, we were inspired by the strides that modern
obstetrics has made since that edition in 1 903. Similarly, we
were humbled by some of the classic challenges that still persist.
Preterm labor, preeclampsia, and infections are some examples.
That said, many of these advances were derived from rigorous,
evidence-based research. And, we acknowledge and support the
power of this academic ideal to further our specialty in the
decades to come.
For this 25th edition, we continue to present the detailed
staples of basic obstetrics such as maternal anatomy and physi­
ology, preconceptional and prenatal care, labor, delivery, and
the puerperium. These accompany detailed discussions of
obstetrical complications exempliied by preterm labor, hemor­
rhage, hypertension, and many more. To emphasize the "M" in
Maternal-Fetal Medicine, we continue to iterate the many
medical and surgical disorders that can complicate pregnancy.
And, our second patient-the fetus-has accrued especial
attention with an entire section devoted to diagnosis and treat­
ment of fetal disorders. For all of these, we once again empha­
size the science-based underpinnings of clinical obstetrics with
special emphasis on biochemical and physiological principles.
As was the hallmark of previous editions, these dovetail with
descriptions of evidence-based practices. Expert clinical pearls
add depth to these discussions and are written for busy practi­
tioners-those "in the trenches."
To accomplish these goals, the text has been updated with
more than 3000 new literature citations through 20 1 7. Nfany
of the nearly 900 igures are new, and these graphs, sonograms,
magnetic resonance images, photographs, photomicrographs,
and data graphs are almost all in vivid color. M uch of the
original artwork was rendered by our own medical illustrators.
lso, as before, we continue to incorporate contemporane­
ous guidelines from professional and academic organizations
such as the American College of Obstetricians and Gynecolo­
gists, the Society for Maternal-Fetal Medicine, the N ational
Institutes of Health and the National Institute for Child
Health and H uman Development, the Centers for Disease
Control and Prevention, and other authoritative sources. Many
of these data are distilled into nearly 1 00 tables, in which infor­
mation has been arranged in an easy read-and-use format. In
addition, several diagnostic and management algorithms are
available to quickly guide practitioners. Although we strive to
cite numerous sources and provide multiple evidence-based
options for such management schemes, we also include our
own clinical experiences drawn from the large obstetrical ser­
vice at Parkland Hospital. We are convinced that these are
disciplined examples of evidence-based obstetrics but quickly
acknowledge that they do not constitute the sole method of
management.
F. Gary Cunningham
Kenneth J. Leveno
Steven L. Bloom
Jodi S. Dashe
Barbara L. Hoffman
Brian M. Casey
Catherine Y. Spong
xiii
ACKNOWLEDGMENTS
During the creation and production of this textbook, we were
fortunate to have the assistance and support of countless tal­
ented professionals both within and outside the Department of
Obstetrics and Gynecology. To begin, we acknowledge that an
undertaking of this magnitude would not be possible without
the unwavering support provided by Dr. Barry Schwarz, Vice­
Chairman, whose financial and academic endorsement has
been essential.
This 25th edition shows a notable absence of three col­
leagues who provided valuable editorial assistance for prior
editions of Williams Obstetrics. Colleagues from the University
of Texas Southwestern Medical Center include Dr. George
Wendel, Jr.-associate editor for the 22nd and 23rd editions­
who has now assumed the important tole of Executive Director
of the American Board of Obstetrics and Gynecology. Dr.
Jeanne Shefield, with her especial expertise in obstetrical and
perinatal infections, has left Dallas and is now the Division
Director of Maternal-Fetal Medicine at Johns Hopkins
University School of Medicine. From the University of
Alabama at Birmingham, Dr. John Hauth, who served as an
editor for the 2 1 st through 23rd editions, provided valuable
contributions to chapters on chronic hypertension, preterm
labor, and labor induction, which have endured in updated
forms in this edition.
We are especially grateful for the contributions of our two
returning Associate Editors. Dr. Mala Mahendroo is a talented
basic scientist who continues to perform a magnificent job of
ptoviding a coherent translational version of basic science
aspects of human reproduction. Dr. Diane Twickler-the con­
summate radiologist-has been an invaluable mentor for our
residents, fellows, and faculty. She adds her fantastic experi­
ences and extensive knowledge regarding clinical and techno­
logical advances related to fetal and maternal imaging to add
considerable depth to this textbook. Dr. Seth Hawkins served
us well as an Associate Editor in this edition and brought addi­
tional strengths to the areas of clinical and academic Maternal­
Fetal Medicine. His rigorous analysis of evidence-based data on
topics of maternal physiology, fetal-growth disorders, obesity,
liver disease, and labor induction has added new perspectives to
these chapters.
To add academic breadths to our endeavor, we have enlisted
new Contributing Editors-all from UT Southwestern Medical
Center-each of whom has expertise in important areas of
maternal and perinatal medicine. From the Division of
Maternal-Fetal Medicine, Dr. C. Edward Wells adds his exten­
sive clinical experience and his incredible skills with prior cesar­
ean delivery and obstetrical sonography. Dr. April Bailey, with
joint appointments in the Departments of Radiology and
Obstetrics and Gynecology, shared her tremendous knowledge
regarding fetal and maternal imaging with sonography, radiog­
raphy, computed tomography, and magnetic resonance tech­
niques. Dr. David Nelson brings strong clinical knowledge
regarding preterm labor, stillbirth, management of obstetrical
hemorrhage, psychiatric disorders in pregnancy, and mul tifetal
gestation. From the Department of Anesthesia, Dr. Weike Tao
provided academic insight and clinical mastery in obstetrical
anesthesia. Similarly, Dr. Erica Grant graciously and skillfully
advanced the discussion of this topic. Dr. Myra Wyckoff, from
the Department of Pediatrics, contributed greatly to chapters
regarding the term and preterm newborn. Her expertise b oth in
normal care and in treatment for the more vulnerable neonates
has greatly strengthened the evidence-based content of these
chapters. In toto, the strength of each contributor has added to
create the sum total of our academic endeavor.
In constructing such an expansive academic compilation, the
expertise of many colleagues was needed to add vital and contem­
poraneous information. It was indeed fortuitous for us to have
access to a pantheon of collaborators from here and from other
academic medical centers. From our own Department of Obstetrics
and Gynecology, our nationally known pelvic anatomist, Dr.
Marlene Corton, prepared graphic masterpieces for the anatomy
chapter. Dr. Elysia Moschos contributed a number of sonographic
images of early pregnancy and uterine malformations. Drs.
Claudia Werner and William Griith lent valuable insight into the
management of cervical dysplasia. Dr. Emily Adhikari was an
invaluable source in the construction of the chapters on maternal
and perinatal infections. Finally, clinical photographs were con­
tributed by many faculty and fellows, who include Drs. Patricia
Santiago-Munoz, Julie Lo, Elaine Duryea, Jamie Morgan, J udith
Head, David Rogers, Kimberly Spoonts, and Emily Adhikari.
From the Department of Radiology, Drs. Michael Landy, Jefrey
Pruitt, and Douglas Sims added insights and provided computed
tomographic and magnetic resonance images. From the
Department of Pathology, Dr. Kelley Carrick generously donated
exemplary photomicrographs. Dr. Kathleen Wilson, director of
the cyrogenomic microarray analysis laboratory, graciously assisted
us in updating our cyrogenomic nomenclature.
We are also indebted to contributions made by our national
and international colleagues. Experts in placental pathology
who shared their expertise and images include Drs. Kurt
Benirschke, Ona Marie Faye-Petersen, Mandolin Ziadie,
Michael Conner, Brian Levenson, Jaya George, and Erika
Fong. Input for hypertensive disorders was provided by Drs.
John Hauth, Marshall Lindheimer, and Gerda Zeeman; for
operative vaginal delivery by Dr. Edward Yeomans; and semi­
nal images were contributed by Drs. Kevin Doody, Timothy
Crombleholme, Michael Zaretsky, Togas T ulandi, Edward
Lammer, Charles Read, Frederick Elder, April Bleich, Laura
Greer, and Roxane Holt.
In addition to these contributors, we relied heavily on our
colleagues in the Division of Maternal-Fetal Medicine. These
professionals, in addition to providing expert content, gra­
ciously assisted us by covering clinical duties when writing and
editing were especially time consuming. These include Drs.
xv
xvi
Acknowledg m ents
Scott Roberts, Oscar Andujo, Vanessa Rogers, Charles Brown,
Julie Lo, Robyn Horsager, Patricia Santiago-Munoz, Shivani
Patel, Elaine Duryea, Jamie Morgan, Morris Bryant, Shena
Dillon, Denisse Holcomb, Robert Stewart, Stephan Shivvers,
Ashley Zink, and Mark Peters. In addition, warm thanks go to
our Residency Director, Dr. Vanessa Rogers, and her Associate
Program Director, Dr. Stephanie Chang, who have created a
nurturing environment for our residents to flourish. Similarly,
our Maternal-Fetal Medicine (MF11) D ivision Associate
Fellowship Director, Dr. Charles Brown, has aided our work
through his talented mentoring of our MFM fellows.
We also emphasize that production of Wiliams Obstetrics
would not be feasible without the help of our Maternal-Fetal
Medicine fellows and our residents in Obstetrics and
Gynecology. Their insatiable curiosity serves to energize us to
ind new and effective ways to convey age-old truths, new data,
and cutting-edge concepts. Their logical and critical questions
lead us to weaknesses in the text, and thereby, always help us to
improve our work. In addition, we sincerely thank them for
their vigilance in capturing photographs of spectacular exam­
ples of both obstetrical pathology and normal indings. For
example, included in this edition are photographs contributed
by Drs. Devin Macias, Maureen Flowers, Paul Slocum,
Jonathan Willms, Stacey Thomas, Kara Ehlers, Nidhi Shah,
Abel Moron, Angela Walker, and Elizabeth Mosier.
This edition is heavily populated with seminal examples of
sonographic indings. We are grateful for the mentorship and
talent of Drs. Diane Twickler and April Bailey; Mary Gibbs,
RD\1S; Rafael Levy, RDMS; Michael Davidson, RDMS; and
the many talented sonographers at Parkland Hospital.
Thanks to generous funding from McGraw-Hill Education,
this 25th edition now contains more than 200 color illustra­
tions. Most of these were crafted by several skilled medical
illustrators who include Ms. Marie Sena, Ms. Erin Frederickson,
Mr. Jordan Pietz, Ms. SangEun Cha, and Ms. Jennifer Hulsey.
All of these talented artists trained here at UT Southwestern
under the tutelage of \1r. Lewis Calver. Additional artistic sup­
port came from Mr. Jason McAlexander and 1I1s. Suzanne
Ghuzzi, of MPS North America LLC, who provided the full­
color graphs and line art used to enhance this edition. Their
team tirelessly coordinated efforts between author and artist
and graciously accommodated our numerous changes and
tweaks.
Production of the 5000-page manuscript would not have
been possible without a dedicated team to bring these efforts
together. Once again, we are deeply indebted to Ms. Dawn
Wilson and Ms. Melinda Epstein for their untiring efforts with
manuscript production. Ms. Mercedes Salinas also provided
excellent, conscientious manuscript assistance. Information
technology support was provided by the very knowledgeable
and responsive Mr. Charles Richards and Mr. Thomas Ames.
For these and many more that go unnamed, we could not have
done our job without their expertise.
It again has been a privilege and a pleasure to work with
the dedicated professionals from McGraw-Hill Education.
Mr. Andrew Moyer has brought his considerable intelligence,
unwavering work ethic, and creativity to this edition of
Williams Obstetrics. His dedication to creating the best text­
book possible equaled our efforts, and we are in awe of his
productive, gracious style. H is assistant, Ms. Jessica Gonzalez,
provided professional, timely, and ever-sunny aid. Mr. Richard
Ruzycka served as production supervisor for this edition of the
textbook. He skillfully kept our project on track through an
array of potential hurdles. Last, we have had the pleasure to
work with Mr. Armen Ovsepyan in coordinating the artwork
for many of our editions. His organization and eiciency are
unrivaled.
Our text took its inal shape under the watchful care of our
compositors at Aptara, Inc. We thank Ms. Indu J awwad for her
talents in graciously and masterfully coordinating and oversee­
ing composition. Her dedicated attention to detail and organi­
zation were vital to completion of our project. Also, at Aptara,
Mr. Mahender Singh performed a crucial task of quality con­
trol. He also assisted, along with Mr. Surendra Mohan Gupta
and Mr. Anil Varghese, in creating beautiful chapter layouts to
highlight our content aesthetically and informatively. This edi­
tion's chapters, for the irst time, were posted and available
online for use prior to print publication. We thank Mr. Braj
Bhushan and Mr. Ashish Kumar Sharma for preparing this
content so brilliantly. Special thanks go to Ms. Kristin Landon.
As copyeditor for now several editions of both Williams
Obstetrics and Williams Gynecoloy, Kristin has added precision
and clarity to our efforts. Her endurance and pleasant profes­
sionalism through many challenging chapters has made our text
better.
Finally-but certainly not last-we acknowledge our sig­
niicant debt to the women who have entrusted themselves and
their unborn children to us for obstetrical care. The clinical
expertise and many graphic illustrations presented in this text
would not have been possible without their collaborative spirit
to help us advance obstetrical knowledge. We also offer enthu­
siastic and heartfelt appreciation to our families and friends.
Without their patience, generosity, love, and encouragement,
this task would have been impossible.
F. Gary Cunningham
Kenneth J. Leveno
Steven L. Bloom
Jodi S. Dashe
Barbara L. Hoffman
Brian M. Casey
Catherine Y. Spong
2
C H A PT E R 1
Ove rvi ew of O b stet r i cs
VITAL STATISTICS
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PREGNANCY RATES IN THE UNITED STATES
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MEASU RES OF OBSTETRICAL CARE
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TIM ELY TOPICS I N OBSTETRICS
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In theolowingpages I have attempted to setorth, as brily
as seemed to be consistent with thoroughness, the scientic
basis or and the practical application of the obstetrical art.
At the same time, I have endeavored to present the more
practical aspects of obstetrics in such a manner as to be of
direct service to the obstetrician at the bedside.
-J. Whitridge Williams ( 1 903)
So reads the introduction to Williams' irst edition of this
textbook, Obstetrics-A Text-Book or the Use of Students and
Practitioners. In this 25th edition, we strive to follow the tenets
described by Williams. And, each chapter begins with a quote
from his original textbook.
he science and clinical practice of obstetrics is concerned
with human reproduction. hrough quality perinatal care, the
specialty promotes the health and well-being of the pregnant
woman and her fetus. Such care entails appropriate recognition
and treatment of complications, supervision of labor and deliv­
ery, initial care of the newborn, and management of the puer­
perium. Postpartum care promotes health and provides family
planning options.
he importance of obstetrics is relected by the use of mater­
nal and neonatal outcomes as an index of the quality of health
and life among nations. Intuitively, indices that refl e ct poor ob­
stetrical and perinatal outcomes would lead to the assumption
that medical care for the entire population is lacking. With
those thoughts, we now provide a synopsis of the current state
of maternal and newborn health in the United States as it relates
to obstetrics.
VITAL STATISTICS
The National Vital Statistics System of the United States is the
oldest and most successful example of intergovernmental data
sharing in public health. This agency collects statistics through
vital registration systems that operate in various jurisdictions.
These systems are legally responsible for registration of births,
fetal deaths, deaths, marriages, and divorces. Legal authority
resides individually with the 50 states; two regions-the Dis­
trict of Columbia and New York City; and ive territories­
American Samoa, Guam, the Northern Mariana Islands, Puerto
Rico, and the Virgin Islands.
The standard birth certifi c ate was revised in 1 989 to include
more information on medical and lifestyle risk factors and
obstetrical practices. In 2003, an extensively revised Standard
Certificate of Live Birth was implemented in the United States.
The enhanced data categories and speciic examples of each are
summarized in Table 1 - 1 . By 20 1 3 , 3 5 states had implemented
the revised birth certificate representing 76 percent of all births
(MacDorman, 20 1 5) . Importantly, the 2003 version of the
population death certificate contains a pregnancy checkbox to
eventually be implemented by all states a oseph, 20 1 7) .
• Definitions
The uniform use of standard deinitions is encouraged by the
World Health Organization as well as the American Academy
of Pediatrics and the American College of Obstetricians and
Gynecologists (20 1 7) . Such uniformity allows data compar­
ison not only between states or regions of the country but
also between countries. Still, not all deinitions are uniformly
Ove rview of Obstetrics
TABLE 1 -1 . Genera l Categories of New I nformation Added to the 2003 Revision of the B i rth Certificate
Risk factors in preg na ncy-Exa m ples: prior preterm b i rth, prior ec l a m psia
Obstet rica l p roced u res-Exa m p l es: tocolys i s, cerclage, external cep h a l i c vers i o n
La bor-Exa m p les: n o n cep h a l i c prese ntat ion, g l ucocorticoids for feta l l u ng matu ration, a nti b i otics d u ri ng l a bo r
De l ivery-Exa m ples: u n s uccessfu l operative vag i na l d e l ive ry, t r i a l o f l a bo r w i t h p r i o r cesa rea n del ivery
N ewborn- Exa m ples: assisted venti l ation, s u rfa cta nt thera py, co ngen ita l a n o m a l ies
applied. For example, the American College of Obstetri­
cians and Gynecologists recommends that reporting include
all fetuses and neonates born weighing at minimum 500 g,
whether alive or dead. But, not all states follow this recom­
mendation. Speciically, 28 states stipulate that fetal deaths
beginning at 20 weeks' gestation should be recorded as such;
eight states report all products of conception as fetal deaths;
and still others use a minimum birthweight of 350 g, 400 g,
or 500 g to deine fetal death. To further the confusion, the
National Vital S tatistics Reports tabulates fetal deaths from
gestations that are 20 weeks or older (Centers for Disease Con­
trol and Prevention, 20 1 6) . his is problematic because the
50th percentile for fetal weight at 20 weeks approximates 325
to 350 g-considerably less than the 500-g deinition. Indeed,
a birthweight of 500 g corresponds closely with the 50th per­
centile for 22 weeks' gestation.
Deinitions recommended by the National Center for
Health Statistics and the Centers for Disease Control and Pre­
vention are as follows:
Perinatal period. The interval between the birth of a neonate
born after 20 weeks' gestation and the 28 completed days
after that birth. When perinatal rates are based on birth­
weight, rather than gestational age, it is recommended that
the perinatal period be deined as commencing at the birth
of a 500-g neonate.
Birth. he complete expulsion or extraction from the mother of
a fetus after 20 weeks' gestation. As described above, in the
absence of accurate dating criteria, fetuses weighing < 500 g
are usually not considered as births but rather are termed
abortuses for purposes of vital statistics.
Birthweight. The weight of a neonate determined immediately
after delivery or as soon thereafter as feasible. It should be
expressed to the nearest gram.
Birth rate. The number of live births per 1 000 population.
Fertility rate. The number of live births per 1 000 females aged
1 5 through 44 years.
Live birth. he term used to record a birth whenever the new­
born at or sometime after birth breathes spontaneously or
shows any other sign of life such as a heartbeat or deinite
spontaneous movement of voluntary muscles. Heartbeats
are distinguished from transient cardiac contractions, and
respirations are diferentiated from fleeting respiratory ef­
forts or gasps.
Stillbirth or fetal death. The absence of signs of life at or after
birth.
Early neonatal death. Death of a liveborn neonate during the
irst 7 days after birth.
Late neonatal death. Death after 7 days but before 29 days.
Stillbirth rate or fetal death rate. The number of stillborn neo­
nates per 1 000 neonates born, including live births and still­
births.
Neonatal mortality rate. The number of neonatal deaths per
1 000 live births.
Perinatal mortality rate. he number of stillbirths plus neonatal
deaths per 1 000 total births.
Infant death. All deaths of liveborn infants from birth through
12 months of age.
Infant mortality rate. The number of infant deaths per 1 000
live births.
Low birthweight. A newborn whose weight is <2500 g.
Very low birthweight. A newborn whose weight is < 1 500 g.
Extremely low birthweight. A newborn whose weight is < 1 000 g.
Term neonate. A neonate born any time ater 37 completed
weeks of gestation and up until 42 completed weeks of gesta­
tion (260 to 294 days) . The American College of Obstetri­
cians and Gynecologists (20 1 6b) and Society for Maternal­
Fetal Medicine endorse and encourage specific gestational age
designations. Eary term refers to neonates born at 37 complet­
ed weeks up to 38 6/7 weeks. Full term denotes those born at 39
completed weeks up to 406r weeks. Last, late term describes
neonates born at 4 1 completed weeks up to 4 1 6/ weeks.
Preterm neonate. A neonate born before 37 completed weeks
(the 259th day) . A neonate born before 34 completed weeks
is early preterm, whereas a neonate born between 34 and 36
completed weeks is late preterm.
Postterm neonate. A neonate born anytime after completion of
the 42nd week, beginning with day 295.
Abortus. A fetus or embryo removed or expelled from the uterus
during the first half of gestation-20 weeks or less, or in the
absence of accurate dating criteria, born weighing < 500 g.
Induced termination of pregnancy. The purposeful interruption
of an intrauterine pregnancy that has the intention other
than to produce a liveborn neonate and that does not result
in a live birth. This deinition excludes retention of products
of conception following fetal death.
Direct maternal death. he death of the mother that results
from obstetrical complications of pregnancy, labor, or the
puerperium and from interventions, omissions, incorrect
treatment, or a chain of events resulting from any of these
factors. An example is maternal death from exsanguination
after uterine rupture.
Indirect maternal death. A maternal death that is not directly
due to an obstetrical cause. Death results from previously
existing disease or a disease developing during pregnancy,
labor, or the puerperium that was aggravated by maternal
physiological adaptation to pregnancy. An example is mater­
nal death from complications of mitral valve stenosis.
3
4
Ove rview
Nonmaternal death. Death of the mother that results from ac­
cidental or incidental causes not related to pregnancy. An
example is death from an automobile accident or concurrent
malignancy.
Maternal mortality ratio. The number of maternal deaths that
result from the reproductive process per 1 00,000 live births.
Used more commonly, but less accurately, are the terms ma­
ternal mortaliy rate or maternal death rate. The term ratio
is more accurate because it includes in the numerator the
number of deaths regardless of pregnancy outcome-for
example, live births, stillbirths, and ectopic pregnancies­
whereas the denominator includes the number of live births.
Pregnancy-associated death. The death of a woman, from any
cause, while pregnant or within 1 calendar year of termina­
tion of pregnancy, regardless of the duration and the site of
pregnancy.
Pregnancy-related death. A pregnancy-associated death that
results from: ( 1 ) complications of pregnancy itself, (2) the
chain of events initiated by pregnancy that led to death, or
(3) aggravation of an unrelated condition by the physiologi­
cal or pharmacological efects of pregnancy and that subse­
quently caused death.
PREGNANCY RATES IN TH E U N ITED STATES
According to the Centers for Disease Control and Prevention
(CDC), the fertility rate of women aged 1 5 to 44 years in the
United States in 20 1 5 was 62.5 live births per 1 000 women
(Martin, 20 1 7) . This rate began slowly trending downward in
1 990 and has now dropped below that for replacement births.
This indicates a population decline (Hamilton, 20 1 2) . There
were 3.98 million births in 20 1 5, and this constituted the lowest
birth rate ever recorded for the United States-1 2.3 per 1 000
population. The birth rate decreased for all major ethnic and
racial groups, for adolescents and unmarried women, and for
those aged 20 to 24 years. For women older than 30 years, the
birth rate rose slightly. Almost half of newborns in 20 1 0 in the
United States were minorities: Hispanic-25 percent, African­
American- 1 4 percent, and Asian-4 percent (Frey, 20 1 1 ) .
h e total number o f pregnancies and their outcomes i n 20 1 5
are shown in Table 1 -2. According to the Guttmacher Institute
(20 1 6b) , 45 percent of births in the United States are unintended
at the time of conception. Importantly, the overall proportion of
unintended births has declined only slightly since 200 1 . Unmar­
ried women, black women, and women with less education or
income are more likely to have unplanned pregnancies.
In Table 1 -2, induced abortion information derives from
CDC abortion surveillance data from 45 states combined with
Guttmacher Institute data on induced abortion. hese data have
been collected beginning in 1 976. Since Roe v. Wade legaliza­
tion of abortion, more than 46 million American women have
chosen legalized abortions. As discussed later, this provides a
compelling argument for easily accessible family planning.
MEASURES OF OBSTETRICAL CARE
• Perinatal Mortality
Several indices are used to assess obstetrical and perinatal
outcomes as measures of medical care quality. As noted, the
perinatal mortality rate includes the numbers of stillbirths and
neonatal deaths per 1 000 total births. In 20 1 3, the perinatal
mortality rate was 9.98 per 1 000 births (Fig. 1 - 1 ) (MacDor­
man, 20 1 5) . There were 25,972 fetal deaths at gestational ages
of 20 weeks or older. Fetal deaths at 28 weeks or more have
been declining since 1 990, whereas rates for those between 20
and 27 weeks are static (Fig. 1 -2) . By way of comparison, there
were a total of 1 9,04 1 neonatal deaths in 2006-meaning that
nearly 60 percent of the perinatal deaths in the United States
were fetal.
• Infant Deaths
here were 6. 1 infant deaths per 1 000 live births in 20 1 3
compared with 6 . 8 i n 200 1 (MacDorman, 20 1 5) . The three
leading causes of infant death-congenital malformations, low
birthweight, and sudden infant death syndrome-accounted
for almost half of all deaths (Heron, 20 1 5) . Infants born at the
lowest gestational ages and birthweights add substantively to
these mortality rates. For example, more than half of all infant
deaths in 2005 were in the 2 percent of infants born before
12
Perinatal mortality rate
TABLE 1-2. Tota l P reg nancies a n d Outcomes in the
U n ited States i n 2015
Outcome
B i rt h s
Cesa rea n d e l iveries
P rete rm b i rt h s « 3 7 wee ks)
Low b i rthwei g h t «2 5 00 g)
I n d u ced a bo rt i o n s
Tota l preg n a n c i esd
Number or Percent
3,988,076
32.2%
9.5%
8.0%
664,435
4,652,51 1
aExciudes sponta neous a bo rtio n s a n d ecto pic preg n a n c i es.
Data from Mart i n , 2 0 1 7.
2005
201 0
Year
201 3
F I G U R E , -, Perinata l morta l ity rates: U n ited States, 2000-20 1 3.
(Reprod uced with permission from MacDorm a n M F, Gregory EC:
Feta l and peri natal morta l ity: U n ited States, 20 1 3. N atl Vita l Stat
Rep. 2 0 1 5 J u l 23;64(8): 1 -24.)
Ove rview of Obstetrics
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15
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1 1 .8
1 1 .4
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201 0
20 1 3
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FIGURE 1 -2 Feta l and neonatal deaths: U n ited States, 2000-20 1 3.
(Modified with permission from MacDorman M F, G regory EC: Feta l
a nd perinata l morta l ity: U n ited States, 20 1 3 . Natl Vita l Stat Rep.
20 1 5 Jul 23;64(8): 1 -24.)
32 weeks' gestation. Indeed, the percentage of infant deaths
related to preterm birth increased from 34.6 percent in 2000
to 36.5 percent in 2005. When analyzed by birthweight, two
thirds of infant deaths were in low-birthweight neonates. Of
particular interest are infants with birthweights < 500 g, for
whom neonatal intensive care can now be ofered.
• Maternal Mortality
As shown in Figure 1 -3, maternal mortality rates dropped
precipitously in the United States during the 20th century.
Pregnancy-related deaths are so uncommon as to be measured
per 1 00,000 births. The CDC (20 1 7a) has maintained data on
pregnancy-related deaths since 1 986 in its Pregnancy Mortality
Surveillance System. In the latest report, Creanga and cowork­
ers (20 1 7) described 2009 pregnancy-related deaths during
the period from 2 0 1 1 to 20 1 3. Approximately 5 percent were
early-pregnancy deaths due to ectopic gestation or abortive out­
comes. he deadly obstetrical triad of hemorrhage, preeclampsia,
and infection has accounted for a third of all deaths (Fig. 1 -4) .
hromboembolism, cardiomyopathy, and other cardiovascular
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Cause of preg nancy-related deaths
FIGURE 1 -4 Six common ca u ses of preg nancy-related deat h s for
the U n ited States, 2006-20 1 0. (Data from Crea n g a, 2 0 1 5.)
disease together accounted for another third. Other signii- .
cant contributors were amnionic luid embolism (5.3 percent)
and cerebrovascular accidents (6.2 percent) . Anesthesia-related
deaths were at an all-time low-only 0.7 percent. Similar causes
were reported for selected cohorts for years 2008 to 2009 and
20 1 3 to 20 1 4 (MacDorman, 20 1 7) .
Shown in Figure 1 -5, the pregnancy-related mortality ratio
of 23.8 per 1 00,000 live births in 20 1 4 is the highest during
the previous 40 years. And, according to the Institute of Health
Metrics, it was 28 per 1 00,000 in 20 1 3 (Tavernise, 2 0 1 6) .
This rise simply may b e that more women are dying, however,
other factors explain this doubling of the rate from 1 990 to
20 1 3 a oseph, 20 1 7) . The irst is an artiicial elevation caused
by the International Statistical Classiication of Diseases, 1 0th
Revision (ICD- I 0) , implemented in 1 999. Second, improved
24
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1 950 1 960 1 970 1 980
1 990 2000
FIGURE 1-3 Materna l morta l ity rates for the U n ited States, 1 9502003. (Data from Berg, 201 0; Hoyert, 2007.)
2002
2004
2006
2008
201 0
201 2
2014
Year
FIGURE 1 -5 Esti mated materna l morta l ity rates in 48 states a n d
t h e District o f Col u m bia. (Data from MacDorm a n, 2 0 1 6.)
5
6
Ove rview
60
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- Non-hispanic black
- H ispanic
- Non-hispanic white
40
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2006
2008
2010
2012
20 14
Year
F I G U R E 1 -6 Trends i n materna l morta l ity ratio (per 1 00,000 l ive
births) by race: U n ited States, 2005-20 1 4. ( Data from Moadda b,
2 0 1 6.)
reporting definitely contributes to the rise (MacDorman,
20 1 6b, 20 1 7) . In the past, maternal deaths were notoriously
underreported (Koonin, 1 997) . Third, and related to the sec­
ond explanation, the rate of rise is at least partially due to the
revised death certificate and its pregnancy checkbox described
earlier (Main, 20 1 5) . Fourth, the number of pregnant women
with severe chronic health conditions, which place women at
higher risk, is greater (Centers for Disease Control and Pre­
vention, 20 1 7a) . Finally, the increased proportion of births to
women older than 40 years contribute to higher mortality rates
(MacDorman, 20 1 7) .
Whatever the cause, the apparent sharp rise o f the mater­
nal mortality rates has galvanized the obstetrical community
to action (Chescheir, 20 1 5) . According to Barbieri (20 1 5) ,
the Joint Commission has recommended that birthing centers
establish standardized protocols and implement simulation
eforts. D'Alton and colleagues (20 1 6) described eforts of a
working group to lower morbidity and mortality rates.
Another consideration is the obvious disparity of higher
mortality rates among black, Hispanic, and white women as
shown in Figure 1 -6. Racial disparities translate to health care
availability, access, or utilization (Howell, 20 1 6; Moaddab,
20 1 6) . And, maternal mortality is disparately high in rural
compared with metropolitan areas (Maron, 20 1 7) .
Importantly, many o f the reported maternal deaths are con­
sidered preventable. Berg and colleagues (2005) estimated that
this may be up to a third of pregnancy-related deaths in white
women and up to half of those in black women. In one evalu­
ation of an insured cohort, 28 percent of 98 maternal deaths
were judged preventable (Clark, 2008) . hus, although signifi­
cant progress has been made, further eforts are imperative for
obstetrics in the 2 1 st century.
• Severe Maternal Morbidity
his serves as another measure to guide prevention eforts.
Lowering medical error rates serves to diminish risks for
maternal mortality or severe maternal morbidity. The
terms near misses or close calls were introduced and defined
as unplanned events caused by error that do not result in
patient injury but have the potential to do so (Institute for
Safe Medication Practices, 2009) . hese are much more com­
mon than inj ury events, but for obvious reasons, they are
more diicult to identiy and quantiy. Systems designed to
encourage reporting have been installed in various institu­
tions and allow focused safety eforts (Clark, 20 1 2; Main,
20 1 7; Shields, 20 1 7) . The American College of Obstetricians
and Gynecologists and the Society for Maternal-Fetal Medi­
cine (20 1 6f) have provided lists of suggested screening topics
for this purpose.
Several data systems now measure indicators of unplanned
events caused by errors that have injurious potential. This evo­
lution followed inadequacies in the ability of hospitalization
coding to reflect the severity of maternal complications. Thus,
coding indicators or modifiers are used to allow analysis of seri­
ous adverse clinical events (Clark, 2 0 1 2 ; King, 20 1 2) . Such a
system was implemented by the World Health Organization.
It has been validated in Brazil and accurately reflects maternal
death rates (Souza, 20 1 2) . Similar systems are in use in Brit­
ain as the UK Obstetric Surveilance System-UKOSS (Knight,
2005, 2008) . In the United States, one example is the National
Partnership for Maternal Safety (D'Alton, 20 1 6 ; Main, 20 1 5) .
T o study severe morbidity, the CDC analyzed more than
50 million maternity records from the Nationwide Inpatient
Sample from 1 998 to 2009 (Callaghan, 20 1 2) . They used ICD9-CM codes and reported that 1 29 per 1 0,000 of these gravi­
das had at least one indicator for severe morbidity (Table 1 -3) .
hus, for every maternal death, approximately 200 women
experience severe morbidity. he CDC (20 1 7b) estimates that
65,000 women per year have such maternal morbidity. These
numbers are greatest in smaller hospitals with < 1 000 deliveries
annually (Hehir, 20 1 7) . Finally, as with mortality rates, there
are serious racial and ethnic disparities for severe maternal mor­
bidity, and black women are disproportionately afected (Cre­
anga, 20 1 4) .
TIMELY TOPICS I N OBSTETRICS
Various topics have been in the forefront for obstetrical provid­
ers in the 4 years since the last edition of this textbook. In the
following, we discuss several of these topics.
• U.S. Health Care in Crisis
Oba m aca re and Med icaid
In a 20 1 6 issue of the Jounal of the American Medical Associa­
tion fAA), then-President Barack Obama presented a sum­
mary of the Afordable Care Act (ACA) , so-called Obamacare.
He described the successes, the challenges ahead, and the policy
implications of the policy (Bauchner, 20 1 6) . He summarized
three lessons from his experiences with the ACA. First, change
is especially diicult in the face of hyperpartisanship. Second,
special interests pose a continued obstacle to change. Third, he
stressed the importance of pragmatism. Here, he was referring
to the pragmatism necessary when the ACA did not work efec­
tively on day 1 of implementation.
Overview of Obstetrics
TABLE 1 -3. Severe Maternal Morbid ity I nd i cators
Acute myoca rd i a l i n fa rction
Acute ren a l fa i l u re
Ad u lt res pi ratory d i stress syn d ro m e
A m n i o n ic fl u i d e m bo l i s m
Ca rd iac a rrest/ventric u l a r fi b r i l lation
Disse m i nated i ntravasc u l a r coag u l atio n
Ecl a m psia
Heart fa i l u re d u ri ng proced u re
I nj u ries of thorax, a bdomen, a n d pelvis
I ntracra n i a l i nj u ries
P u e rpera l cerebrovascu l a r d i so rd e rs
P u l mona ry edema
Seve re a nesthesia compl ications
Sepsis
Shock
S i c kle-ce l l c r i s i s
Th rom botic e m b o l i s m
Ca rd iac m o n itori ng
Conversion of card iac rhyt h m
Hyste rectom y
Ca rd iac s u rg ery
Trach eostom y
Venti lation
S u m ma rized from the Centers for Di sease Control and
P reve ntion, 20 1 7 b.
At this same time, draconian cuts to Medicaid were being
proposed, and President Obama ended his JM1A report with a
quotation from John Kasich, the Republican governor of Ohio.
"For those that live in the shadows of life, those who are the
least among us, I will not accept the fact that the most vulner­
able in our state should be ignored. We can help them."
hese potential efects to Medicaid ripple into the specialty
of obstetrics. In 20 1 0, it was estimated that Medicaid insured
48 percent of the births in the United States (lvlarkus, 20 1 3) .
Importantly, Medicaid covered a disproportionate number
of complicated births. Speciically, Medicaid insured more
than half of all hospital stays for preterm and low-birthweight
infants and approximately 45 percent of infant hospital stays
due to birth defects.
Repeal a n d Repl ace
he young, healthy Americans who were expected to finan­
cially bolster the ACA ultimately enrolled in insuicient num­
bers to ensure long-term ACA sustainability. hus, long-term
options included repair or repeal of the ACA. hroughout
Donald Trump's campaign for the presidency of the United
States, he made repeal of the ACA a focus of his candidacy.
As of this writing, both the United S tates House of Repre­
sentatives and the Senate have grappled with "repeal and
replace" for 6 months. According to the Congressional Budget
Oice, this action would result in 23 million Americans losing
health care insurance and cuts in Medicaid dollars (Fiedler,
20 1 7) . he latter was to be accomplished by transferring fund­
ing of Medicaid from the Federal government to the states.
hese potential outcomes have prompted considerable debate
among voters, and "repeal and replace" has become politically
charged. Currently, the Senate has been unable to recruit suf­
icient Republican votes for Senate passage of such a bill. We
suggest that the health care crisis should be reframed and redi­
rected instead to a critical analysis of health care costs and
resource utilization.
Materna l a n d I nfa nt Hea lth Ca re Costs
he Centers for Medicare and Medicaid Services estimated
that spending on health care in the United States in 20 1 5
accounted for 1 7.8 percent of the gross domestic product­
GDP (Voelker, 20 1 0) . he total amount of health-care spend­
ing-$3.2 trillion-equated to an estimated $ 1 0,000 per
person. Moreover, compared with 1 2 other high-income coun­
tries, health-care spending in the United States as a proportion
of GDP was approximately 50 percent more than the next
highest country. Yet, health-care outcomes, which included
infant mortality rates, were worse in the United States. And,
approximately two thirds of U.S. infant deaths result from
complications stemming from preterm births (Matthews,
20 1 5) . Indeed, in its 20 1 0 annual global Premature Birth
Report Card, the United States garnered a grade of "D" from
the March of Dimes for its recognition and p revention of pre­
term labor in the more than 540,000 neonates born annually
before 37 weeks' gestation.
Causes for the excessive health care costs in the United States
are attributed, in part, to greater use of medical technology and
excessive prices (Squires, 20 1 7) . Two recent studies demon­
strate the detrimental efect of obstetrics on health care costs.
The first report by Nelson and coworkers (20 1 7) described the
inefectiveness of 1 7 -alpha hydroxyprogesterone caproate ( 1 7OHP-C) to prevent recurrent preterm birth. Methodology for
this trial is presented in Chapter 42 (p. 8 1 7) . Several lessons can
be learned from this investigation. First, use of 1 7-OHP-C was
legitimized in the United States by a national consensus com­
mittee using expert opinion. hese opinions were promulgated,
despite FDA reservations that the evidence was lacking in sev­
eral important respects. However, once approved, 1 7 -OH P-C
was sold by one pharmaceutical company for $ 1 500 for a sin­
gle, 2 50-mg injectable dose. Remarkably, this same dose could
be compounded and purchased for $25 from local pharmacies.
In the subsequent price-gouging controversy, members of the
United States Congress intervened to permit continued use of
the less expensive 1 7-0 HP-C.
he second study is a multisite prospective trial of the efec­
tiveness of transvaginal sonography to screen for cervical-length
shortening to predict preterm birth (Esplin, 20 1 7) . A total of
94 1 0 nulliparous women were studied. he Society for Mater­
nal-Fetal Medicine and the American College of Obstetricians
and Gynecologists (20 1 6d) both legitimized universal cervical­
length screening in their joint Committee Opinion (Bloom,
20 1 7) . And, by 20 1 5 , one survey of 78 Maternal-Fetal Medi­
cine fellowship programs showed that 68 percent were using
universal cervical-length screening to predict preterm birth
(Khalifeh, 20 1 7) . It was estimated that a modest Medicaid rate
of $237 per cervical-length ultrasound would result in approxi­
mately $350 million in added health care costs. But, Esplin and
7
8
Overvi ew
associates (20 1 7) found that routine screening for a short cer­
vix was not beneficial. hat is, a widely used intervention was
actually inefective. his is a clear example of how unproven
technology can seep into widespread practice.
These two reports highlight a substantial problem in U.S.
health care, namely, inefective yet expensive interventions
introduced into broad use without robust evidence. These two
reports also speak to a demand for robust scientific evidence.
Scrutiny of other ingredients in the health-care paradigm such
as prices for hospitalization, prices for surgical procedures, and
prices charged by health insurance companies may illuminate
similar contributions to the health care fiscal crisis.
• Cesarean Delivery Rate
In past editions of this textbook, the rising cesarean delivery
rate was considered problematic. his rate has leveled, but there
are still imperatives in progress to help lower this rate. One col­
lateral source of cesarean delivery morbidity is from the grow­
ing incidence of morbidly adherent placentas encountered in
women with a prior hysterotomy incision, discussed in Chap­
ters 31 and 4 1 .
• Genomic Technology
Breakthroughs in fetal testing and diagnosis continue to stun.
By 20 1 2, prenatal gene microarray techniques were used for
clinical management (Dugof, 20 1 2) . he advantages of these
techniques are outlined in Chapters 1 3 and 1 4. Wapner and
coworkers (20 1 2) compared chromosomal microarray analysis
of maternal blood with karyotyping for chromosomal anoma­
lies. Reddy and associates (20 1 2) applied this technology to still­
birth evaluation and reported it to be superior to karyotyping.
Another report by Talkowski and colleagues (20 1 2) described
whole-genome sequencing of a fetus using maternal blood.
Screening for fetal aneuploidy using cell-free DNA (cDNA)
was first introduced in 20 1 1 . The technique is described in
Chapter 1 4 (p. 284) , and it is based on isolation of free fetal
(placental) DNA in maternal blood. In a landmark study,
Norton and associates (20 1 5) found that cDNA had a higher
sensitivity and speciicity compared with standard prenatal
screening for trisomy 2 1 fetuses. Still, invasive testing is cur­
rently necessary to confirm a positive cDNA test result (Chitty,
20 1 5; Snyder, 20 1 5) .
• The Ob/Gyn Hospitalist
he term "hospitalist" was coined in the 1 990s and referred to
physicians whose primary professional focus was generalized care
of hospitalized patients. From this concept came the obstetrical
and gynecological hospitalist whose primary role was to care for
hospitalized obstetrical patients and to help manage their emer­
gencies. These physicians could also provide urgent gynecological
care and emergency department consultation. Alternative terms
include "obstetrical hospitalist" or "laborist," but the preferred
standardized term by the American College of Obstetricians and
Gynecologists (20 1 6e) is "Ob/Gyn hospitalist."
lthough not a recognized subspecialty of obstetrics and
gynecology, the Ob/Gyn hospitalist movement has gained
momentum. he Society of Ob-Gyn Hospitalists had 528
members in 20 1 7 (Burkard, 20 1 7) . Various practice models
are described to fit the needs of a wide spectrum of obstetri­
cal volumes (McCue, 20 1 6) . In addition to providing lifestyle
modifi c ations, Ob/Gyn hospitalists are used by some hospitals
to improve the quality and safety of their women's services
and to reduce adverse events. Aside from a possible lowering
of the labor induction rate, studies are needed to demonstrate
improved outcomes with these providers (American College of
Obstetricians and Gynecologists, 20 1 6e; Srinivas, 20 1 6) .
• Medical Liability
he American College of Obstetricians and Gynecologists peri­
odically surveys its fellows concerning the efect of liability on
their practice. he 20 1 5 Survey on Professional Liability is the
1 2th such report since 1 983 (Carpentieri, 20 1 5) . From this
survey, it appears that there is still a "liability crisis," and the
reasons for it are complex. Because it is largely driven by money
and politics, a consensus seems unlikely. Although some inter­
ests are diametrically opposite, other factors contribute to the
problem's complexity. For example, each state has its own laws
and opinions on tort reform. In some states, annual premiums
for obstetricians approach $300,000-expenses that at least
partially are borne by the patient and certainly by the entire
health-care system. In 2 0 1 1 , all tort costs in the United States
totaled nearly $265 billion. his is an astounding 1 .8 percent of
the gross domestic product and averages to a cost of $838 per
citizen (Towers Watson, 20 1 5) .
he American College o f Obstetricians and Gynecologists
(20 1 6a,c) has taken a lead in adopting a fair system for mal­
practice litigation-or maloccurrence itigation. And nationally,
there is the possibility of federl tort reform under the Trump
administration (Lockwood, 20 1 7; Mello, 20 1 7) .
• Home Births
Following a slight decline from 1 990 through 2004, the per­
centage of out-of-hospital births in the United States increased
from 0.86 to 1 . 5 percent-almost 75 percent-through 20 1 4
(MacDorman, 20 1 6a) . O f these home births, only a third are
attended by nurse midwives certiied by the American Midwife
Certiication Board (Grtinebaum, 20 1 5; Snowden, 20 1 5) .
Proponents o f home births cite successes derived from lauda­
tory observational data from England and he Netherlands (de
Jonge, 20 1 5; Van der Kooy, 20 1 1 ) . Data from the United States,
however, are less convincing and indicate a higher incidence of
perinatal morbidity and mortality (Grtinebaum, 20 14, 20 1 5;
Snowden, 20 1 5; Wasden, 20 1 4; Wax, 20 1 0) . hese latter find­
ings have led Chervenak and coworkers (20 1 3, 20 1 5) to ques­
tion the ethics of participation in planned home births. Greene
and Ecker (20 1 5) take a broader view. Given data from these
more recently cited studies, they are of the view that these data
empower women to make a rational decision regarding home
delivery. he American College of Obstetricians and Gynecolo­
gists (20 1 7b) believes that hospitals and accredited birth centers
ofer the safest settings, but that each woman has the right to
make a medically informed decision regarding delivery.
Overview of Obstetrics
IVF-conceived livebon neonate in Sweden (Brinnstrom, 2015).
• Family Planning Services
Politics and religion over the years have led to various govern­
mental interferences with the reproductive rights of women.
These intrusions have disparately afected indigcm women and
adolescents. This is despite all reports of the overwhelming suc­
cess of such programs. One example is the exclusion of Planned
Parenthood ailiates from the Texas Medicaid fee-for-service
family planning program. In some groups of women served,
there was discontinuation of contraception and an increased
rate of Medicaid binhs (Stevenson, 2 0 1 6),
According to t h e G urrmacher Institute (20 1 6a), publicly
funded family planning services are needed by 20 million
American women. In 2014, such services prevenred nearly
2 million unintended pregnancies and 700,000 abonions in
the United States. The fate of family planning services is not
fully determined, while waiting for decisions regarding provi­
sions within the 20 1 7 American Healrh Care Ace (AHCA). or
"Trumpcare." In his response ro news that the AHCA may dis­
mantle cOlHraceptive coverage, American College of Obstetri­
cians and Gynecologises President Dt. Haywood Brown (20 1 7)
called this a deep disregard for women's health.
During pregnancy, the mother was treated with t:lcrol imus, aza­
thioprine, and corticosteroids and underwent cesarean delivery
at 32 weeks for preeclampsia and abnormal feral heart rate test­
ing. This was followed by uterine trmsplamation programs at the
C1cvebnd Clinic and Baylor Medical Center in Dallas (F1yckt.
2016. 2017, Testa. 2017). In 2017. the Swedish team had com­
pleted a nine-patient trial, in which seven women had become
pregnant and ive had sllccessful deliveries (Kuehn, 2017). Also,
in Dallas, the irst such newbon in the Unired Stares was born
(Rice. 20 1 7).
Meanwhile, researchers a t Children's Hospital of Philadel­
phia pursued a 20-year goal in search of an artiicial womb
(Yuko, 2 0 1 7). Using incubatOr technology, [he team devised an
artiicial amnionic sac. hrough this, (he umbilical vessels were
perfused and drained, and the blood was retuned to systems
[hat performed exrracorporeal membrane oxygenation and
dialysis. To date, lamb fetuses have been kept alive for as long
as 1 month. Adverse efects of cerebrovascular hypotension and
hypoxemia are conjectural but highly worrisome.
1he ethical and legal challenges of these new technologies
are daunting. Of those that arose from IVF, mOSt are setded.
For the Q[her twO endeavors, there are likely many years of ethi­
• Opioid Abuse in Pregnancy
cal and legal milestones ahead.
According to the CDC (20 1 4). there were 259 million pre­
scriptions written in 20 1 2 for opioid medications. In 20 1 3 ,
more than a rhird o f American adults reported prescrip­
tion opioid use (Han, 2 0 1 7) . These fteely available-albeit
requiring a prescription-addictive drugs are associated with
opioid use disorders. It remains uncercain if opioid use is tera­
rogenic (Lind, 201 7). Still, their abuse by pregnam women
has caused an unprecedented rise i n the 1eonata/ abstinence
syndrome. described furrher in Chapters 1 2 (p. 248) and 33
(p. 625). Treatment of opioid abuse in pregnancy and its
sequelae result i n $ 1 . 5 billion annually in hospital charges.
For obstetrical providers ro bener deal with opioid-addicted
pregnant women and their fetus-newborns, the Eu.nice Kennedy
Shriver National Institute of Child Helth and Human Devel­
opment convened a workshop in 2016 co study many aspecrs of
the problem (Reddy. 2017). he Workshop was cosponsored by
the American College of Obstetricians and Gynecologisrs, the
American Academy of Pediatrics, the Society for Maternal-Fetal
Medicine, the CDC, and the March of Dimes. Several copies
were addressed, and hopefully implementation of these indings
will help improve maternal treatment and neonatal outcomes
(American College of Obstetricians and Gynecologists. 2017a).
• Brave New World
The bold new concept of in-vitro fercilization (IVF) produced
the irst IVF baby in Britain in 1978. This was soon followed
in 1 9 8 1 with an American success. After four decades. the Soci­
ety for Assisted Reproductive Technology (SART) reports that
more than 1 million babies have been born in the United States
using assisted reproductive technologies (ART) ofered by 440
clinics (Fox. 2017).
ter IS years of experimental preparation. the promise of a
successful human uterine transplant was finally realized with
n
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14
C H A PT E R 2
Mate rn a l A n ato my
ANTERIOR ABDOMINAL WALL . . . . . . . . . . . . . . . . . . . . . 1 4
EXTERNAL GENERATIVE ORGANS . . .
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I NTERNAL GENERATIVE ORGANS . . . . . . . . . .
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. 23
LOWER URI NARY TRACT STRUCTU RES
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16
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28
MUSCU LOSKELETAL PELVIC ANATOMY
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29
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.
As the mechanism oflabour is essentialy a process ofaccom­
modation between theoetus and the passage through which
it must pass, it is apparent that obstetrics lacked a scientiic
oundation until the anatomy of the bony pelvis and of the
sot parts connected with it was cleary understood
-J. Whitridge Williams ( 1 903)
ANTERIOR ABDOMINAL WALL
• Skin, Subcutaneous Layer, and Fascia
he anterior abdominal wall confines abdominal viscera,
stretches to accommodate the expanding uterus, and provides
surgical access to the internal reproductive organs. hus, a com­
prehensive knowledge of its layered structure is required to sur­
gically enter the peritoneal cavity.
Langer lines describe the orientation of dermal fibers within
the skin. In the anterior abdominal wall, they are arranged
transversely. As a result, vertical skin incisions sustain greater
lateral tension and thus, in general, develop wider scars. In con­
trast, low transverse incisions, such as the Pfannenstiel, follow
Langer lines and lead to superior cosmetic results.
The subcutaneous layer can be separated into a superficial,
predominantly fatty layer-Camper fascia, and a deeper mem­
branous layer-Scarpa fascia. Camper fascia continues onto the
perineum to provide fatty substance to the mons pubis and
labia majora and then to blend with the fat of the ischioanal
fossa. Scarpa fascia continues inferiorly onto the perineum as
Colles fascia, described on page 1 9.
Beneath the subcutaneous layer, the anterior abdominal wall
muscles consist of the midline rectus abdominis and pyramida­
lis muscles as well as the external oblique, internal oblique, and
transversus abdominis muscles, which extend across the entire
wall (Fig. 2- 1 ) . The ibrous aponeuroses of these three latter
muscles form the primary fascia of the anterior abdominal wall.
These fuse in the midline at the linea alba, which normally mea­
sures 10 to 1 5 mm wide below the umbilicus (Beer, 2009) . n
abnormally wide separation may reflect diastasis recti or hernia.
These three aponeuroses also invest the rectus abdominis
muscle as the rectus sheath. The construction of this sheath
varies above and below a boundary, termed the arcuate line
(see Fig. 2- 1 ) . Cephalad to this border, the aponeuroses invest
the rectus abdominis bellies on both dorsal and ventral surfaces.
Caudal to this line, all aponeuroses lie ventral or supericial to
the rectus abdominis muscle, and only the thin transversalis
fascia and peritoneum lie beneath the rectus (Loukas, 2008).
This transition of rectus sheath composition can be seen best in
the upper third of a midline vertical abdominal incision.
he paired small triangular pyramidalis muscles originate
from the pubic crest and insert into the linea alba. These mus­
cles lie atop the rectus abdominis muscle but beneath the ante­
rior rectus sheath.
• Blood Supply
he supericial epigastric, supericial circumlex iliac, and super­
icial external pudendal arteries arise from the femoral artery
just below the inguinal ligament within the femoral triangle
Mate r n a l Anatomy
--- Internal thoracic a .
Rectus a bd o m i n i s m .
--- Linea a I ba
Externa l o b l i q u e m .
I ntern a l o b l i q u e m .
S u perior epigastric a .
Tra nsversus a bd o m i n i s m .
Lateral cuta neous n .
Anterio r rectus sheath (cut edges)
Inferior epigastric a .
Posterior rectus sheath
Arcuate l i ne
Anterio r s u perior i l i a c spine
Tra nsvers a l i s fascia
External obl i q u e a po n e u rosis
I n g u i n a l l ig a m ent
Su perfi c i a l c i rc u m flex i l i a c a.
External p u d e n d a l a .
Genita l b ra nch of genitofemora l n .
La b i u m m aj u s
S u perfi cial i n g u i n a l ring
with emerg i ng rou n d l i g a m ent,
i l io i n g u i n a l & gen itofe mo ra l n n .
F I G U R E 2 - 1 Anterior a bdom i n a l wa l l a natomy. (Mod ified with permission from Co rton M M : Anatomy. I n Hoffman B L, Schorge J O,
Bradshaw KD, et al (eds): Wi l l iams Gynecology, 3 rd ed. New York, McGraw- H i l i Education, 2 0 1 6 )
(see Fig. 2- 0 . These vessels supply the skin and subcutaneous
layers of the anterior abdominal wall and mons pubis. Of these
three, the superficial epigastric vessels are surgically important
to the obstetrician and course diagonally from their origin
toward the umbilicus. With a low transverse skin incision, these
vessels can usually be identified at a depth halway between the
skin and the anterior rectus sheath. They lie above Scarpa fascia
and several centimeters from the midline. Ideally, these vessels
are identiied and surgically occluded.
In contrast, the inferior "deep" epigastric vessels are branches
of the external iliac vessels and supply anterior abdominal wall
muscles and fascia. Of surgical relevance, the inferior epigastric
vessels initially course lateral to, then posterior to the rectus
abdominis muscles, which they supply. Above the arcuate line,
these vessels course ventral to the posterior rectus sheath and
lie between this sheath and the posterior surface of the rec­
tus muscles. Near the umbilicus, the inferior epigastric vessels
anastomose with the superior epigastric artery and vein, which
are branches of the internal thoracic vessels. Clinically, when
a Maylard incision is used for cesarean delivery, the inferior
epigastric vessels may be lacerated lateral to the rectus belly dur­
ing muscle transection. Preventively, identiication and surgical
occlusion are preferable. These vessels rarely may rupture fol­
lowing abdominal trauma and create a rectus sheath hematoma
(Toicher, 20 1 0; Wai, 20 1 5) .
On each side o f the lower anterior abdominal wall, Hes­
selbach triangle is the region bounded laterally by the inferior
epigastric vessels, inferiorly by the inguinal ligament, and medi­
ally by the lateral border of the rectus abdominis muscle. Her­
nias that protrude through the abdominal wall in Hesselbach
triangle are termed direct inguinal hernias. In contrast, indirect
inguinal hernias do so through the deep inguinal ring, which
lies lateral to this triangle, and then may exit out the supericial
inguinal ring.
• Innervation
he entire anterior abdominal wall is innervated by inter­
costal nerves (T 7-" ) the subcostal nerve (T ' 2 ) ' and the ilio­
'
hypogastric and the ilioinguinal nerves (L, ) . Of these, the
15
16
Matern a l An ato my a nd P hysiol ogy
I ntecostal n .
Anterior ramus
Internal
oblique m.
External _ _.
oblique m .
Lateral
The ilioinguinal and iliohypogastric nerves can be severed
during a low transverse incision or entrapped during closure,
especially if incisions extend beyond the lateral borders of the
rectus abdominis muscle (Rahn, 20 1 0) . These nerves carry
sensory information only, and injury leads to loss of sensation
within the areas supplied. Rarely, chronic pain may develop
(Whiteside, 2005) .
he T 10 dermatome approximates the level of the umbilicus.
Analgesia to this level is suitable for labor and vaginal birth.
Regional analgesia for cesarean delivery or for puerperal steril­
ization ideally extends to T4 '
EXTERNAL GENERATIVE ORGANS
F I G U R E 2-2 I ntercostal and s u bcosta l nerves a re the a nterior
ra m i of spinal nerves. I n this fig u re, a n i ntercostal nerve extends
ventra l l y between the tra n sversu s a bd o m i n i s a n d i nternal oblique
m u scles. D u ring this path, the nerve g ives rise to latera l a n d a nte­
rior cuta neous bra nches, which i n nervate the a nterior a bd o m i n a l
wa l l . A s shown b y t h e i n serted need le, the tra nsvers u s a bd o m i n i s
plane (TAP) block takes advantage o f this a n atomy. (Mod ified with
perm ission from Hawki ns J L: Anesthesia for the preg n a nt wom a n .
I n Yeoma n s ER, Hoffma n B L, G i l strap L C I I I, e t a l : C u n n i n g h a m a n d
G i l stra ps's Operative Obstetrics, 3 rd e d . N e w York, McGraw H i l l
Ed u cation, 201 7.)
intercostal and subcostal nerves are anterior rami of the
thoracic spinal nerves and run along the lateral and then
anterior abdominal wall between the transversus abdominis
and internal oblique muscles (Fig. 2-2) . his space, termed
the transversus abdominis plane, can be used for postcesar­
ean analgesia blockade (Chap. 2 5 , p. 500) (Fusco, 20 1 5 ;
Tawfik, 20 1 7) . O thers report rectus sheath or ilioinguinal­
iliohypogastric nerve blocks to decrease postoperative pain
(Mei, 20 1 1 ; Wolfson, 20 1 2) .
Near the rectus abdominis lateral borders, anterior branches
of the intercostal and subcostal nerves pierce the posterior
sheath, rectus muscle, and then anterior sheath to reach the skin.
hus, these nerve branches may be severed during a Pfannenstiel
incision creation during the step in which the overlying anterior
rectus sheath is separated from the rectus abdominis muscle.
In contrast, the iliohypogastric and ilioinguinal nerves origi­
nate from the anterior ramus of the first lumbar spinal nerve.
They emerge lateral to the psoas muscle and travel retroperito­
neally across the quadratus lumborum inferomedially toward
the iliac crest. Near this crest, both nerves pierce the transver­
sus abdominis muscle and course ventromedially. At a site 2
to 3 cm medial to the anterior superior iliac spine, the nerves
then pierce the internal oblique muscle and course supericial
to it toward the midline (Whiteside, 2003). The iliohypo­
gastric nerve perforates the external oblique aponeurosis near
the lateral rectus border to provide sensation to the skin over
the suprapubic area (see Fig. 2- 1 ) . The ilioinguinal nerve in
its course medially travels through the inguinal canal and exits
through the supericial inguinal ring, which forms by splitting
of external abdominal oblique aponeurosis fi b ers. This nerve
supplies the skin of the mons pubis, upper labia majora, and
medial upper thigh.
• Vulva
Mons P ub is, La bia, a n d Cl itoris
The pudenda-commonly designated the vulva-includes all
structures visible externally from the symphysis pubis to the
perineal body. This includes the mons pubis, labia majora and
minora, clitoris, hymen, vestibule, urethral opening, greater
vestibular or Bartholin glands, minor vestibular glands, and
paraurethral glands (Fig. 2-3) . he vulva receives innervations
and vascular support from the pudendal nerve (p. 22) .
he mons pubis is a fat-illed cushion overlying the symphy­
sis pubis. After puberty, the mons pubis skin is covered by curly
hair that forms the triangular escutcheon, whose base aligns
with the upper margin of the symphysis pubis. In men and
some hirsute women, the escutcheon extends farther onto the
anterior abdominal wall toward the umbilicus.
Labia majora usually are 7 to 8 cm long, 2 to 3 cm wide,
and 1 to 1 . 5 cm thick. They are continuous directly with the
mons pubis superiorly, and the round ligaments terminate at
their upper borders. Hair covers the labia majora, and apocrine,
eccrine, and sebaceous glands are abundant. Beneath the skin,
a dense connective tissue layer is nearly void of muscular ele­
ments but is rich in elastic fibers and fat. his fat mass provides
bulk to the labia majora and is supplied with a rich venous
plexus. During pregnancy, this vasculature may develop vari­
cosities, especially in multiparas, from increased venous pres­
sure created by the enlarging uterus. hey appear as engorged
tortuous veins or as small grapelike clusters, but they are typi­
cally asymptomatic and require no treatment.
Each labium minus is a thin tissue fold that lies medial to
each labium majus. he labia minora extend superiorly, where
each divides into two lamellae. From each side, the lower lamel­
lae fuse to form the frenulum of the clitoris, and the upper
lamellae merge to form the prepuce (see Fig. 2-3). Inferiorly,
the labia minora extend to approach the midline as low ridges
of tissue that join to form the fourchette. The labia minora
dimensions vary greatly among individuals, with lengths from
2 to 10 cm and widths from 1 to 5 cm (Lloyd, 2005) .
Structurally, the labia minora are composed of connec­
tive tissue with numerous vessels, elastin ibers, and very few
smooth muscle ibers. hey are supplied with many nerve
endings and are extremely sensitive (Ginger, 20 1 1 a; Schober,
20 1 5) . The epithelia of the labia minora difer with location.
Thinly keratinized stratiied squamous epithelium covers the
Maternal Anatomy
La bia m i nora
Mons pu bis
S kene g land
openings
Bartholin gland
openi ngs
G l a ns of cl itoris
Fre n u l u m
� '\"
�..
_
_
_
_
La b i u m maj u s
La b i u m m i n u s
, :,---
open i n g
I
�--r,
Fou rc h ette
Fossa navicu l a ris
I nfe rior fa scia of
l evator a n i m m ./
pelvic d i a p h ra g m
Peri n e a l body
Anus
Exte rn a l a n a l
s p h i n cter m .
F I G U R E 2-3 Vu lva r structu res and s u bcuta neous layer of the a nterior peri nea l tri a n g l e. Note the conti n u ity of Colles a nd Scarpa fasciae.
I n set: Vesti b u l e bounda ries a nd open i n g s onto vesti b u le. (Reproduced with permission from Corton MM: Anatomy. In Hofm a n BL, Schorge
JO, Bradshaw KD, et a l (eds): Wi l l ia m s Gynecology, 3 rd ed. New York, McG raw- H i l i Ed u cation, 201 6.)
outer surface of each labium. On their inner surface, the lateral
portion is covered by this same epithelium up to a demarcating
line, termed Hart line. Medial to this line, each labium is cov­
ered by squamous epithelium that is nonkeratinized. he labia
minora lack hair follicles, eccrine glands, and apocrine glands.
However, sebaceous glands are numerous (Wilkinson, 20 1 1 ) .
h e clitoris i s the principal female erogenous organ. I t is
located beneath the prepuce, above the frenulum and urethra,
and projects downward and inward toward the vaginal open­
ing. The clitoris rarely exceeds 2 cm in length and is composed
of a glans, a corpus or body, and two crura (Verkauf, 1 992) .
he glans is usually less than 0 . 5 cm in diameter, is covered
by stratified squamous epithelium, and is richly innervated.
he clitoral body contains two corpora cavernosa. Extending
from the clitoral body, each corpus cavernosum diverges lat­
erally to form a long, narrow crus. Each crus lies along the
inferior surface of its respective ischiopubic ramus and deep to
the ischiocavernosus muscle. The clitoral blood supply stems
from branches of the internal pudendal artery. Specifically, the
deep artery of the clitoris supplies the clitoral body, whereas
the dorsal artery of the clitoris supplies the glans and prepuce.
Vest i b u l e
I n adult women, the vestibule i s a n almond-shaped area that is
enclosed by Hart line laterally, the external surface of the hymen
medially, the clitoral frenulum anteriorly, and the fourchette
posteriorly (see Fig. 2-3) . The vestibule is usually perforated
by six openings: the urethra, the vagina, two Bartholin gland
ducts, and two ducts of the largest paraurethral glands-the
Skene glands. he posterior portion of the vestibule between
the fourchette and the vaginal opening is called the fossa navic­
ularis. It is usually observed only in nulliparas.
The bilateral Bartholin glands, also termed greater vestibular
glands, measure 0.5 to 1 cm in diameter. On their respective
side, each lies inferior to the vestibular bulb and deep to the
inferior end of the bulbospongiosus muscle (former bulbocav­
ernosus muscle) . A duct extends medially from each gland,
measures 1 . 5 to 2 cm long, and opens distal to the hymeneal
ring-one at 5 and the other at 7 o'clock on the vestibule. Fol­
lowing trauma or infection, either duct may swell and obstruct
to form a cyst or, if infected, an abscess. In contrast, the minor
vestibular glands are shallow glands lined by simple mucin­
secreting epithelium and open along Hart line.
he paraurethral glands are a collective arborization of
glands whose numerous small ducts open predominantly along
the entire inferior aspect of the urethra. he two largest are
called Skene glands, and their ducts typically lie distally and
near the urethral meatus. Clinically, inlammation and duct
obstruction of any of the paraurethral glands can lead to ure­
thral diverticulum formation. The urethral opening or meatus
is in the midline of the vestibule, 1 to 1 . 5 cm below the pubic
arch, and a short distance above the vaginal opening.
• Vagina and Hymen
In adult women, the hymen is a membrane of varying thickness
that surrounds the vaginal opening more or less completely.
17
18
Materna l Anatomy a nd P hys i o l ogy
It is composed mainly of elastic and collagenous connective
tissue, and both outer and inner surfaces are covered by non­
keratinized stratified squamous epithelium. he aperture of the
intact hymen ranges in diameter from pinpoint to one that
admits one or even two ingertips. As a rule, the hymen is torn
at several sites during irst coitus. However, identical tears may
form by other penetration, for example, by tampons used dur­
ing menstruation. The edges of the torn tissue soon reepithelial­
ize. In pregnant women, the hymeneal epithelium is thick and
rich in glycogen. Changes produced in the hymen by childbirth
are usually readily recognizable. For example, over time, the
hymen transforms into several nodules of various sizes, termed
hymeneal or myrtiform caruncles.
Proximal to the hymen, the vagina is a musculomembra­
nous tube that extends to the uterus and is interposed length­
wise between the bladder and the rectum (Fig. 2-4) . Anteriorly,
the vagina is separated from the bladder and urethra by con­
nective tissue-the vesicovaginal septum. Posteriorly, between
the lower portion of the vagina and the rectum, similar tissues
together form the rectovaginal septum. The upper fourth of the
vagina is separated from the rectum by the rectouterine pouch,
also called the cul-de-sac or pouch of Douglas.
Normally, the anterior and posterior walls of the vaginal
lumen lie in contact, with only a slight space intervening at the
lateral margins. Vaginal length varies considerably, but com­
monly, the anterior wall measures 6 to 8 cm, whereas the pos­
terior vaginal wall is 7 to 1 0 cm. The upper end of the vaginal
vault i s subdivided by the cervix into anterior, posterior, and
two lateral fornices. Clinically, the internal pelvic organs usu­
ally can be palpated through the thin walls of these fornices.
The vaginal lining is composed of nonkeratinized strati­
fied squamous epithelium and underlying lamina propria. In
premenopausal women, this lining is thrown into numerous
thin transverse ridges, known as rugae, which line the anterior
and posterior vaginal walls along their length. Deep to this, a
muscular layer contains smooth muscle, collagen, and elastin.
Beneath this muscularis lies an adventitial layer consisting of
collagen and elastin (Weber, 1 997) .
The vagina lacks glands. Instead, it is lubricated by a tran­
sudate that originates from the vaginal subepithelial capillary
plexus and crosses the permeable epithelium (Kim, 20 1 l ) . Due
to increased vascularity during pregnancy, vaginal secretions are
notably increased. At times, this may be confused with amni­
onic fl u id leakage, and clinical diferentiation of these two is
described in Chapter 22 (p. 435).
Mter birth-related epithelial trauma and healing, fragments
of stratified epithelium occasionally are embedded beneath
the vaginal surface. Similar to its native tissue, this buried epi­
thelium continues to shed degenerated cells and keratin. As a
result, epidermal inclusion cysts, which are filled with keratin
debris, may form. hese are a common vaginal cyst.
The vagina has an abundant vascular supply. The proximal
portion is supplied by the cervical branch of the uterine artery
and by the vaginal artery. he latter may variably arise from the
Posterior vag i n a l forni x
Vesicocervical space (septu m )
Posterior cu l -de-sac
of Dou g l a s
Vesicouteri ne peritonea l
reflection
Med ian u m b i l ica l
liga ment ( u rachus)
Rectovag i n a l space �-n\
(fi l led with loose
con nective tissue)
I ntern a l anal =--�
sphincter m .
Vesicova g i n a l space
(fi l led with loose
con nective tissue)
Externa l a n a l
s p h i n cter m .
Peri neal body
Fused d ista l segment
of urethra & vag i na
F I G U R E 2-4 Vag i na a nd su rrou n d i n g a n atomy. (Reprod uced with permission from Corton MM: Anatomy. I n Hofm a n BL, Schorge JO,
Brad shaw KD, et al (eds): Wi l l i a m s Gynecology, 3 rd ed. New York, McGraw- H i l i Education, 201 6.)
Maternal A n atomy
uterine or inferior vesical artery or directly from the internal iliac
artery. The middle rectal artery contributes supply to the poste­
rior vaginal wall, whereas the distal walls receive contributions
from the internal pudendal artery. At each level, vessels supply­
ing each side of the vagina course medially across the anterior or
posterior vaginal wall and form m idline anastomoses.
An extensive venous plexus also surrounds the vagina and
follows the course of the arteries. Lymphatics from the lower
third, along with those of the vulva, drain primarily into the
inguinal lymph nodes. Those fro m the middle third drain into
the internal iliac nodes, and those from the upper third drain
into the external, internal, and common iliac nodes.
• Perineum
his diamond-shaped area between the thighs has boundaries
that mirror those of the bony pelvic outlet: the pubic symphy­
sis anteriorly, ischiopubic rami and ischial tuberosities antero­
laterally, sacrotuberous ligaments posterolaterally, and coccyx
posteriorly. An arbitrary line joining the ischial tuberosities
divides the perineum into an anterior triangle, also called the
urogenital triangle, and a posterior triangle, termed the anal
triangle.
he perineal body is a fi b romuscular pyramidal mass found
in the midline at the junction between these anterior and pos­
terior triangles (Fig. 2-5) . Also called the central tendon of the
perineum, the perineal body sonographically measures 8 mm
tall and 1 4 mm wide and thick (Santoro, 20 1 6) . It serves as
the junction for several structures and provides significant peri­
neal support (Shafi k , 2007) . Superficially, the bulbospongiosus,
superficial transverse perineal, and external anal sphincter mus­
cles converge on the perineal body. More deeply, the perineal
membrane, portions of the pubococcygeus muscle, and internal
anal sphincter contribute (Larson, 20 1 0) . The perineal body
is incised by an episiotomy incision and is torn with second-,
third-, and fourth-degree lacerations.
S u perfi c i a l Space of the Anterior Tri a n g l e
This triangle i s bounded b y the pubic rami superiorly, the ischial
tuberosities laterally, and the supericial transverse perineal mus­
cles posteriorly. It is divided into supericial and deep spaces by
the perineal membrane. This membranous partition is a dense
ibrous sheet that was previously known as the inferior fascia
of the urogenital diaphragm. The perineal membrane attaches
laterally to the ischiopubic rami, medially to the distal third of
the urethra and vagina, posteriorly to the perineal body, and
anteriorly to the arcuate ligament of the pubis (see Fig. 2-5) .
The supericial space of the anterior triangle is bounded
deeply by the perineal membrane and supericially by Co lIes
fascia. As noted earlier, Colles fascia is the continuation of
Scarpa fascia onto the perineum. On the perineum, Co lIes fas­
cia securely attaches laterally to the pubic rami and fascia lata of
the thigh, inferiorly to the supericial transverse perineal muscle
and inferior border of the perineal membrane, and medially to
the urethra, clitoris, and vagina. As such, the superficial space of
the anterior triangle is a relatively closed compartment.
his supericial pouch contains several important struc­
tures, which include the Bartholin glands, vestibular bulbs,
clitoral body and crura, branches of the pudendal vessels
and nerve, and the ischiocavernosus, bulbospongiosus, and
supericial transverse perineal muscles. Of these muscles, the
ischiocavernosus muscles each attach on their respective side
to the medial aspect of the ischial tuberosity inferiorly and
the ischiopubic ramus laterally. Anteriorly, each attaches to a
clitoral crus and may help maintain clitoral erection by com­
pressing the crus to obstruct venous drainage. he bilateral
bulbospongiosus muscles overlie the vestibular bulbs and
Isc h i ocavernosus m .
Crus of cl i to riS
Isch i o p u b i c ra m u s
Vesti b u l a r b u l b
C u t e d g e o f Col les fa scia
B u l bosp o n g i osus m .
( Ba rt h o l i n )
G reater vest i b u l a r
g la n d
C u t e d g e of
ischi ocave rnous m .
Peri n e a l m e m b ra n e
I sch i a l tuberOSity
Peri n e a l m e m b ra n e
S u pe rfic i a l transverse
peri neal m.
Pe ri neal body
/
Extern a l a n a l s p h i n ct e r m .
�
Levator a n i m .
G l uteus m a xi m u s m .
F I G U R E 2 - 5 Su perficial space o f the a nterior peri neal tria n g le a n d posterior peri nea l triang le. Structu res o n t h e left s i d e o f the i m a g e can
be seen after remova l of Col les fa sci a . Those on the right side a re noted after rem ova l of the su perficial m u sc les of the a nterior tria ng le.
(Mod ified with permission from Corton MM: Anatomy. I n Hoffm a n BL, Schorge JO, B radshaw KD, et a l (eds): Wi l l i a m s Gynecology, 3rd ed.
New York, McGraw- H i l i Educatio n, 2 0 1 6.)
19
20
Mate r n a l A natomy a nd Physiol ogy
U rethra . The female urethra measures 3 to 4 cm and originates
within the bladder trigone (p. 28) . he distal two thirds of the
urethra are fused with the anterior vaginal wall. The epithe­
lial lining of the urethra changes from transitional epithelium
proximally to nonkeratinized stratiied squamous epithelium
distally. The walls of the urethra consist of two layers of smooth
muscle, an inner longitudinal and an outer circular. This is in
turn surrounded by a circular layer of skeletal muscle referred
to as the sphincter urethrae or rhabdosphincter (see Fig. 2-6) .
Approximately at the junction of the middle and lower third of
the urethra, and just above or deep to the perineal membrane,
two strap skeletal muscles called the urethrovaginal sphincter
and compressor urethrae are found. Together with the sphincter
urethrae, these constitute the striated urogenital sphincter com­
plex. This complex supplies constant tonus and provides emer­
gency relex contraction to sustain continence.
Distal to the level of the perineal membrane, the walls of
the urethra consist of ibrous tissue, serving as the nozzle that
directs the urine stream. Here, the urethra has a prominent sub­
mucosal layer that is lined by hormonally sensitive stratiied
squamous epithelium. Within the submucosal layer on the dor­
sal (vaginal) surface of the urethra lie the paraurethral glands,
described earlier (p. 1 7) .
h e urethra receives its blood supply from branches o f the
inferior vesical, vaginal, or internal pudendal arteries. Although
still controversial, the pudendal nerve is believed to innervate
the most distal part of the striated urogenital sphincter complex.
Somatic eferent branches from 5 2-54 that course along the infe­
rior hypogastric plexus variably innervate the sphincter urethrae.
Bartholin glands. They attach to the body of the clitoris ante­
riorly and the perineal body posteriorly. The muscles constrict
the vaginal lumen and aid release of secretions from the Bar­
tholin glands. They also may contribute to clitoral erection by
compressing the deep dorsal vein of the clitoris. The bulbos­
pongiosus and ischiocavernosus muscles also pull the clitoris
downward. Last, the superficial transverse perineal muscles
are narrow strips that attach to the ischial tuberosities laterally
and the perineal body medially. They may be attenuated or
even absent, but when present, they contribute to the perineal
body (Corton, 20 1 6) .
The vestibular bulbs are almond-shaped aggregations of
veins that lie beneath the bulbospongiosus muscle on either
side of the vestibule. They measure 3 to 4 cm long, 1 to 2 cm
wide, and 0.5 to 1 cm thick. The bulbs terminate inferiorly at
approximately the middle of the vaginal opening and extend
upward toward the clitoris. Their anterior extensions merge in
the midline, below the clitoral body. During childbirth, veins
in the vestibular bulbs may be lacerated or even rupture to cre­
ate a vulvar hematoma enclosed within the supericial space of
the anterior triangle (Fig. 4 1 - 1 1 , p. 765) .
Deep S pace of the Ante rior Tr i a n g l e
his space lies deep to the perineal membrane and extends up
into the pelvis (Mirilas, 2004) . In contrast to the supericial
perineal space, the deep space is continuous superiorly with the
pelvic cavity (Corton, 2005) . It contains portions of urethra and
vagina, certain portions of internal pudendal artery branches, and
muscles of the striated urogenital sphincter complex (Fig. 2-6) .
Dorsa l v. o f clito ri s
Sphincter urethrae m .
.
Compr essor urethrae m
Urethrovaginal sphincter m .
La b i u m m i n u s (cut)
}
Striated
uroge nital
sphincter
complex
Hymeneal ri ng
Ischiopubic ramus (cut)
Peri neal mem b rane
Isch iopu bic ra m u s
B u l bospong iosus m . (cut) _
-�- Cut edge of peri neal membrane
Compressor urethrae m .
Ureth rova g i n a l s p h i n cter m .
Ischiocavern ous m. (cut)
S u perficial transverse
peri n e a l m .
Extern a l a n a l sphincter m .
Gl uteus max i m us m.
�
�
----�-�.
"S
.
.�
.�
,
-.
.
Pubococcygeus
(pubovisceral) m .
Pub"ecto'"
m.
lliococcygeus
m.
}
Levat or a n i m m .
F I G U R E 2-6 Deep space of a nterior tria n g l e of the peri n e u m . Structures on the right side of the i mage can be seen after remova l of the
peri nea l membrane. Also shown a re structures that attach to the peri neal body: bu l bospong iosus, su perficial transverse perineal, external
anal s p h i n cter, and pu boperi nea lis m u sc les a s we l l as peri neal mem brane. (Reprod uced with perm ission from Corton MM: Anatomy. I n
Hoffm a n BL, Schorge JO, Bradshaw KD, e t a l (eds): Wi l liams Gynecology, 3 rd ed. New York, McGraw- H i l i Ed ucation, 20 1 6.)
Mate r n a l A n atomy
Pe l vic Dia p h ra g m
Found deep t o the anterior and posterior triangles, this broad
muscular sling provides substantial support to the pelvic vis­
cera. The pelvic diaphragm is composed of the levator ani and
the coccygeus muscles. The levator ani, in turn, contains the
pubococcygeus, puborectalis, and iliococcygeus muscles. The
pubococcygeus muscle is also termed the pubovisceral muscle
and is subdivided based on points of insertion and function.
These include the pubovaginalis, puboperinealis, and puboa­
nalis muscles, which insert into the vagina, perineal body, and
anus, respectively (Kearney, 2004) .
Vaginal birth conveys signiicant risk for damage to the
levator ani or to its innervation (DeLancey, 2003; Weidner,
2006) . Evidence supports that levator ani avulsion may pre­
dispose women to greater risk of pelvic organ prolapse (Dietz,
2008; Schwertner-Tiepelmann, 20 1 2) . For this reason, current
research eforts are aimed at minimizing these injuries.
Posterior Tria ng l e
his triangle contains the ischioanal fossae, anal canal, and anal
sphincter complex, which consists of the internal anal sphinc­
ter, external anal sphincter, and puborectalis muscle. Branches
of the pudendal nerve and internal pudendal vessels are also
found within this triangle.
Isch ioa nal Fossae. Also known as ischiorectal fossae, these
two fat-filled wedge-shaped spaces are found on either side of
the anal canal and comprise the bulk of the posterior triangle
(Fig. 2-7) . Each fossa has skin as its supericial base, whereas
its deep apex is formed by the junction of the levator ani and
obturator internus muscles. Other borders include: laterally,
the obturator internus muscle fascia and ischial tuberosity;
inferomedially, the anal canal and sphincter complex; supero­
medially, the inferior fascia of the downwardly sloping levator
ani; posteriorly, the gluteus maxim us muscle and sacrotuberous
ligament; and anteriorly, the inferior border o f the anterior tri­
angle.
The fat found within each fossa provides support to sur­
rounding organs yet allows rectal distention during defecation
and vaginal stretching during delivery. Clinically, injury to ves­
sels in the posterior triangle can lead to hematoma formation
in the ischioanal fossa, and the potential for large accumulation
in these easily distensible spaces. Moreover, the two fossae com­
municate dorsally, behind the anal canal. This can be especially
important because an episiotomy infection or hematoma may
extend from one fossa into the other.
Anal Canal. his distal continuation of the rectum begins at the
level of levator ani attachment to the rectum and ends at the
anal skin. Along this 4- to 5-cm length, the mucosa consists of
columnar epithelium in the uppermost portion. However, at the
pectinate line, also termed dentate line, simple stratified squa­
mous epithelium begins and continues to the anal verge. At the
verge, keratin and skin adnexa join the squamous epithelium.
The anal canal has several tissue layers (see Fig. 2-7) . Inner
layers include the anal mucosa, the internal anal sphincter, and
an intersphincteric space that contains continuation of the rec­
tum's longitudinal smooth muscle layer. An outer layer con­
tains the puborectalis muscle as its cephalad component and
the external anal sphincter caudally.
Within the anal canal, three highly vascularized submucosal
arteriovenous plexuses, termed anal cushions, aid complete clo­
sure of the canal and fecal continence when apposed. Increasing
uterine size, excessive straining, and hard stool create increased
pressure that ultimately leads to degeneration and subsequent
laxity of the cushion's supportive connective tissue base. These
cushions then protrude into and downward through the anal
canal. This leads to venous engorgement within the cushions­
now termed hemorrhoids. Venous stasis results in inflamma­
tion, erosion of the cushion's epithelium, and then bleeding.
Lon g it u d i n a l s m ooth
m. layer
Obturator
i ntern u s m .
\.
t
C i rc u l a r s mooth
m. l a ye r
Levator a n i m ·m .
--
Pl icae t ra nsversa l i s recti
& vessel s i n
Pudendal n .
p u d e n d a l ca n a l
External a n a l s p h i n cter m .
I ntern a l a n a l s p h i ncter m .
.
FIGURE 2-7 Anal ca nal a n d isch ioa n a l fossa. (Reprod uced with perm ission from Corton MM: Anatomy. I n H offma n B L, Schorge JO,
B radshaw KD, et a l (eds): Wi l l i a m s Gynecology, 3 rd ed. New York, McG raw- H i l i Ed ucation, 201 6.)
21
22
Mate r n a l A n atomy a n d Phys i ology
External hemorrhoids are those that arise distal to the pec­
tinate line. They are covered by stratiied squamous epithelium
and receive sensory innevation from the inferior rectal nerve.
Accordingly, pain and a palpable mass are typical complaints.
Following resolution, a hemorrhoidal tag may remain and is
composed of redundant anal skin and ibrotic tissue. In con­
trast, internal hemorrhoids are those that form above the pecti­
nate line and are covered by insensitive anorectal mucosa. hese
may prolapse or bleed but rarely become painful unless they
undergo thrombosis or necrosis.
Anal Sphincter Complex. Two sphincters surround the anal
canal to provide fecal continence-the external and internal
anal sphincters. Both lie near the vagina and may be torn
during vaginal delivery. he internal anal sphincter (lAS) is a
distal continuation of the rectal circular smooth muscle layer.
It receives predominantly parasympathetic ibers, which pass
through the pelvic splanchnic nerves. long its length, this
sphincter is supplied by the superior, middle, and inferior rectal
arteries. he lAS contributes the bulk of anal canal resting pres­
sure for fecal continence and relaxes prior to defecation. The
lAS measures 3 to 4 cm in length, and at its distal margin, it
overlaps the external sphincter for 1 to 2 cm (DeLancey, 1 997) .
he distal site at which this overlap ends, called the intersphinc­
teric groove, is palpable on digital examination.
In contrast, the external anal sphincter (EAS) is a striated
muscle ring that anteriorly attaches to the perineal body and pos­
teriorly connects to the coccyx via the anococygeal ligament. The
EAS maintains a constant resting contraction to aid continence,
provides additional squeeze pressure when continence is threat­
ened, yet relaxes for defecation. he external sphincter receives
blood supply from the inferior rectal artery, which is a branch
of the internal pudendal artery. Somatic motor ibers from the
inferior rectal branch of the pudendal nerve supply innervation.
Clinically, the AS and EAS may be involved in third- and fourth­
degree lacerations during vaginal delivery, and reunion of these
rings is integral to defect repair (Chap. 27, p. 532) .
P u d e n d a l N erve
This is formed from the anterior rami of S 24 spinl nerves. It
courses between the piriformis and cocygeus muscles and exits
through the greater sciatic foramen at a location posterior to the
sacrospinous ligament and just medil to the ischial spine (Barber,
2002; Maldonado, 20 1 5) . Thus, when injecting local anesthetic
for a pudendal nerve block, the ischial spine serves an identifi­
able landmark (Chap. 25, p. 489). The pudendal nerve then runs
beneath the sacrospinous ligament and above the sacrotuberous
ligament as it reenters the lesser sciatic foramen to course along the
obturator internus muscle. Atop this muscle, the nerve lies within
the pudendal canal, also known as Alcock canal, which is formed
by splitting of the obturator internus investing fascia (Shafik,
1 999). In general, the pudendal nerve is relatively fixed as it courses
behind the sacrospinous ligament and within the pudendal canal.
Accordingly, it may be at risk of stretch injury during downward
displacement of the pelvic floor during childbirth (Lien, 2005).
he pudendal nerve leaves this canal to enter the perineum
and divides into three terminal branches (Fig. 2-8). The first of
these, the dorsal nerve of the clitoris, runs between the ischio­
cavernosus muscle and perineal membrane to supply the clitoral
glans (Ginger, 20 1 1 b). Second, the perineal nerve runs superi­
cial to the perineal membrane (Montoya, 20 1 l ) . It divides into
I l i oi n g u i n a l & gen itofe m o ra l n n . b ranches
La b i u m m aj u s & m i n u s (cut)
Posterior labial n .
Isch iocavernosus m .
Bu l bospon g iosus m .
S u perfiCi a l tra nsverse
peri neal m .
Peri neal n .
Pude n d a l n .
I sch i oa n a l fossa
Exte rn a l a na l
s p h i ncter m .
Levator a n i m m .
Glans & crus of cl itoriS
Striated u rogen ital
s ph i ncter m m .
/
/'
Isch i o p u b i c ra m u s
Peri n ea l m e m bra n e w ith
w i n dow that exposes
striated u rogenital
s p h i n cter m m .
l.��:-- Dorsa l n . & a . of
A'-- -::.
; �,.o. �
cl itoriS
Peri neal n. & a .
Peri n ea l bra nch of
posterior fe mora l
cuta neous n .
I nferior rectal n . & a .
Gl ute u s m a x i m u s m .
F I G U R E 2 - 8 Pudenda l nerve a nd vessels. (Reproduced with permission from Corton MM: Anatomy. I n Hoffm a n BL, Schorge JO, Bradshaw KD,
et al (eds): Wi l l iams Gynecology, 3 rd ed. New York, McGraw- H i l i Ed u cation, 20 1 6.)
Materna l A natomy
posterior labial branches and muscular branches, which serve
the labial skin and the anterior perineal triangle muscles, respec­
tively. Last, the inferior rectal branch runs through the ischioanal
fossa to supply the external anal sphincter, the anal mucosa, and
the perianal skin (vlahakkanukrauh, 2005). The major blood
supply to the perineum is via the internal pudendal artery, and
its branches mirror the divisions of the pudendal nerve.
I NTERNAL GENERATIVE ORGANS
• Uterus
The nonpregnant uterus lies in the pelvic cavity between the
bladder anteriorly and the rectum posteriorly. Almost the entire
posterior wall of the uterus is covered by serosa, that is, visceral
peritoneum (Fig. 2-9) . The lower portion of this peritoneum
forms the anterior boundary of the rectouterine cul-de-sac, or
pouch of Douglas. Only the upper portion of the anterior uter­
ine wall is covered by visceral peritoneum. At the caudal border
of this portion, the peritoneum relects forward onto the bladder
dome to create the vesicouterine pouch. As a result, the lower
portion of the anterior uterine wall is separated from the poste­
rior wall of the bladder only by a well-defined loose connective
tissue layer-the vesicouterine space. Clinically, during cesarean
delivery, the peritoneum of the vesicouterine pouch is sharply
incised, and the vesicouterine space is entered. Dissection cau­
dally within this space lifts the bladder safely of the lower uter­
ine segment for hysterotomy and delivery (Chap. 30, p. 573) .
The uterus is pear shaped and consists of two major but
unequal parts. The upper, larger portion is the body or corpus,
whereas the lower smaller cervix projects into the vagina. The
isthmus is the union site of these two. It is of special obstetrical
Cervix
This portion of the uterus is cylindrical and has small aper­
tures at each end-the internal and external cervical ora. The
endocervical canal runs through the cervix and connects these
ora. The cervix is divided into upper and lower portions by the
vagina's attachment to its outer surface. he upper portion­
the portio supravaginalis-begins at the internal os, which cor­
responds to the level at which the peritoneum is reflected up
onto the bladder (Fig. 2- 1 0) . The lower cervical portion pro­
trudes into the vagina as the portio vaginalis.
Before childbirth, the external cervical os is a small, regular,
oval opening. After labor, especially vaginal childbirth, the orifice
c
a
I
b
significance because it forms the lower uterine segment dur­
ing pregnancy. At each superolateral margin of the body is a
uterine cornu, from which a fallopian tube emerges. This area
also contains the origins of the round and ovarian ligaments.
Between the points of fallopian tube insertion is the convex
upper uterine segment termed the fundus.
The bulk of the uterine body, but not the cervix, is muscle.
The inner surfaces of the anterior and posterior walls lie almost
in contact, and the cavity between these walls forms a mere
slit. The nulligravid uterus measures 6 to 8 cm in length com­
pared with 9 to 10 cm in multiparas. The uterus averages 60 g
and typically weighs more in parous women (Langlois, 1 970;
Sheikhazadi, 20 1 0) .
Pregnancy stimulates remarkable uterine growth due to
muscle iber hypertrophy. The uterine fundus, a previously flat­
tened convexity between tubal insertions, now becomes dome
shaped. Moreover, the round ligaments appear to insert at the
junction of the middle and upper thirds of the organ. The fallo­
pian tubes elongate, but the ovaries grossly appear unchanged.
a
b
c
Anterior
A
B
Lateral
Posterior
F I G U R E 2-9 Anterior (A), r i g h t late ra l (8), and posterior ( C ) views o f the uterus of a n a d u lt wom a n . a
c ova ria n l iga ment; Ur u reter.
=
=
=
ovid u ct; b
=
rou n d ligament;
23
24
Mate r n a l An atomy a n d Physiology
Tu bal & ova ri a n b ra nches
of uteri n e & ova ria n a a .
Inferior epigastric a . & n .
Uteri n e fu n d u s
�
1!
Extern a l i l iac a .
E n d o m etri u m
I
Uteri n e a .
\
A
�
�
�'
�((- f l
Uterosacral l i ga ment
Ova ri a n vessels
Ureter
\
-
l�
:r!l
Fa l lo p i a n tu be
r
_�-
/
Intern a l i l iac a .
l----
Uteroova ria n l i gament
---
�
Round l i g a m ent
/ ,
/
�l�
b
Fi..J
I
�
�
/
Isth m u s
1-- Infu n d i b u lopelvic
�
:
Broad l ig a ment
l i g a ment
Portio s upravag i n a l i s
of cervix
portio vag i n a l is of cervix
Ureter
Poste rior
vag inal wa l l (cut)
Peritoneum ( cut)
FIGURE 2-1 0 Uterus, ad nexa, and associated anatomy. (Reprod uced with permission from Corton MM: Anatomy. In Hoffm a n BL, Schorge JO,
Brads haw KD, et al (ed s): Wi l l iams Gynecology, 3 rd ed . New York, McGraw- H i l i Ed ucation, 20 1 6.)
is converted into a transverse slit that is divided such that there
are the so-called anterior and posterior cervical lips. If torn deeply
during labor or delivery, the cervix may heal in such a manner
that it appears irregular, nodular, or stellate (Fig. 36- 1 , p. 653) .
The cervical surface that radially surrounds the external os
is called the ectocervix and is lined predominantly by nonkera­
tinized stratified squamous epithelium. In contrast, the endo­
cervical canal is covered by a single layer of mucin-secreting
columnar epithelium, which creates deep cleftlike infoldings or
"glands. " Commonly during pregnancy, the endocervical epi­
thelium moves out and onto the ectocervix in a physiological
process termed eversion (Chap. 4, p. 5 1 ) .
The cervical stroma is composed mainly o f collagen, elastin,
and proteoglycans, but very little smooth muscle. As described
in Chapter 2 1 (p. 409) , changes in the amount, composition,
and orientation of these components lead to cervical ripening
prior to labor onset. In early pregnancy, increased vascularity
within the cervix stroma beneath the epithelium creates an
ectocervical blue tint that is characteristic of Chadwick sign.
Cervical edema leads to softening-Goodell sign, whereas isth­
mic softening is Hegar sign.
Myo metri u m a n d End ometr i u m
Most o f the uterus i s composed o f myometrium, which con­
tains smooth muscle bundles united by connective tissue
with many elastic fi b ers. Interlacing myometrial ibers sur­
round myometrial vessels and contract to compress these. This
anatomy allows hemostasis at the placental site during the third
stage of labor.
he number of myometrial muscle ibers varies by location
(Schwalm, 1 966) . Levels progressively diminish caudally such
that, in the cervix, muscle makes up only 1 0 percent of the tissue
mass. The uterine body's inner wall has relatively more muscle
than its outer layers. And, in the anterior and posterior walls, the
muscle content is greater than in the lateral walls. During preg­
nancy, the upper myometrium undergoes marked hypertrophy,
but cervical muscle content does not change significantly.
The uterine cavity is lined with endometrium, which is
composed of an overlying epithelium, invaginating glands,
and a supportive, vascular stroma. As discussed in Chapter 5
(p. 83) , the endometrium varies greatly throughout the men­
strual cycle. This layer is divided into a functionalis layer, which
is sloughed with menses, and a basalis layer, which serves to
regenerate the functionalis layer following each menses. During
pregnancy, the endometrium is termed decidua and undergoes
dramatic hormonally driven alterations.
• Ligaments
Several ligaments extend from the uterine surface toward the
pelvic sidewalls and include the round, broad, cardinal, and
uterosacral ligaments (Figs. 2- 1 0 and 2- 1 1) . Despite their
appellation, the round and broad ligaments provide no sub­
stantial uterine support, which contrasts with the cardinal and
uterosacral ligaments.
he round ligament originates somewhat below and anterior
to the origin of the fallopian tubes. Clinically, this orientation can
aid fallopian tube identification during puerperal sterilization.
Mate rnal A n atomy
U reter
Fa l l o p i a n t u be
Isch i a l s p i n e
Extern a l i l iac a . & v .
B l a d d e r t ri g o n e
Arc u s ten d i n e u s fascia pelvis
Arcu s tend i n e u s fascia rectovag i n a l is
Pa rava g i n a l tissue ( p a raco l p i u m )
Latera l vag i n a l s u l c u s
Adventiti a l l a y e r o f a n teri o r va g i n a l wa l l
Rectum
FIGURE 2-1 1 Pelvic viscera and their con nective tissue s u p port. (Reprod uced with permission from Corton MM: Anatomy. In Hoffm a n BL,
Schorge JO, B radshaw KD, et al (eds): Wi l l iams Gynecology, 3 rd ed. New York, McGraw- H i l i Education, 20 1 6.)
his is important if pelvic adhesions limit tubal mobility and
thus, hinder fimbria visualization and tubal confirmation prior
to ligation. Each round ligament extends laterally and down into
the inguinal canal, through which it passes, to terminate in the
upper portion of the ipsilateral labium majus. Sampson artery, a
branch of the uterine artery, runs within this ligament. In non­
pregnant women, the round ligament varies from 3 to 5 mm in
diameter and is composed of smooth muscle bundles separated
by ibrous tissue septa (Mahran, 1 965). During pregnancy, these
ligaments undergo considerable hypertrophy and increase appre­
ciably in both length and diameter.
The broad ligaments are two winglike structures that extend
from the lateral uterine margins to the pelvic sidewalls. Each
broad ligament consists of a double-layer drape of peritoneum.
The anterior and posterior layers of this drape are termed the
anterior and posterior leaves, respectively. In forming the broad
ligament, this peritoneum folds over structures extending from
each cornu. Peritoneum that folds over the fallopian tube is
termed the mesosalpinx, that around the round ligament is the
mesoteres, and that over the ovarian ligament is the mesovarium.
Peritoneum that extends beneath the imbriated end of the fallo­
pian tube toward the pelvic wall forms the suspensory ligament or
the infundibulopelvic ligament of the ovary. This contains nerves
and the ovarian vessels, and during pregnancy, these vessels, espe­
cially the venous plexuses, are dramatically enlarged. Speciically,
the diameter of the ovarian vascular pedicle increases from 0.9
cm to reach 2.6 cm at term (Hodgkinson, 1953) .
The cardinal ligament-also called the transverse cervical lig­
ament or Mackenrodt ligament-anchors medially to the uterus
and upper vagina. The cardinal ligament is the thick base of the
broad ligament. As such, during cesarean hysterectomy, sturdy
clamps and suture are required for its transection and ligation.
Each uterosacral ligament originates with a posterolateral
attachment to the supravaginal portion of the cervix and inserts
into the fascia over the sacrum, with some variations (Rama­
nah, 20 1 2; Umek, 2004) . These ligaments are composed of
connective tissue, small bundles of vessels and nerves, and some
smooth muscle. Covered by peritoneum, these ligaments form
the lateral boundaries of the pouch of Douglas.
The term parametrium is used to describe the connective
tissues adjacent and lateral to the uterus within the broad
ligament. Paracervical tissues are those adjacent to the cervix,
whereas paracolpium is that tissue lateral to the vaginal walls.
• Pelvic Blood Supply
During pregnancy, there is marked hypertrophy of the uter­
ine vasculature, which is supplied principally from the uter­
ine and ovarian arteries (see Fig. 2- 1 0) . The uterine artery,
a main branch of the internal iliac artery-previously called
the hypogastric artery-enters the base of the broad ligament.
he uterine artery courses medially to the lateral side of the
uterus. Approximately 2 cm lateral to the cervix, the uter­
ine artery crosses over the ureter. This proximity is of great
25
26
Maternal Anatomy a nd P hysiology
surgical signiicance, as the ureter may be inj ured or ligated
during hysterectomy when the uterine vessels are clamped and
ligated.
Once the uterine artery has reached the supravaginal por­
tion of the cervix, it divides. The smaller cervicovaginal artery
supplies blood to the lower cervix and upper vagina. The main
uterine artery branch rurns abruptly upward and travels cepha­
lad along the lateral margin of the uterus. Along its path, this
main artery provides a branch of considerable size to the upper
cervix and then numerous other medial branches serially pen­
etrate the body of the uterus to form the arcuate arteries. As
indicated by the name, each branch arches across the organ by
coursing within the myometrium j ust beneath the serosal sur­
face. Arcuate vessels from each side anastomose at the uterine
midline. Radial artery branches originate at right angles from
the arcuate arteries and travel inward through the myometrium,
enter the endometrium/decidua, and branch there to become
either basal arteries or coiled spiral arteries. he spiral arteries
supply the funcrionalis layer. Also called the straight arteries,
the basal arteries extend only into the basalis layer.
As the uterine artery courses cephalad, it gives rise to Samp­
son artery of the round ligament. Just before the main uterine
artery vessel reaches the fallopian rube, it divides into three ter­
minal branches. The ovarian branch of the uterine artery forms
an anastomosis with the terminal branch of the ovarian artery;
I ntern a l i l i a c a.
Extern a l i l i a c a .
the rubal branch makes its way through the mesosalpinx and
supplies part of the fallopian tube; and the fundal branch pen­
etrates the uppermost uterus.
In addition to the uterine artery, the uterus receives blood
supply from the ovarian artery (see Fig. 2- 1 0) . This artery is a
direct branch of the aorta and enters the broad ligament through
the infundibulopelvic ligament. At the ovarian hilum, it divides
into smaller branches that enter the ovary. As the ovarian artery
runs along the hilum, it also sends several branches through the
mesosalpinx to supply the fallopian rubes. Its main stem, how­
ever, traverses the entire length of the broad ligament toward
the uterine cornu. Here, it forms an anastomosis with the ovar­
ian branch of the uterine artery. This dual uterine blood supply
creates a vascular reserve to prevent uterine ischemia if ligation
of the uterine or internal iliac artery is performed to control
postpartum hemorrhage.
Uterine veins accompany their respective arteries. As such,
the arcuate veins unite to form the uterine vein, which empties
into the internal iliac vein and then the common iliac vein.
Some of the blood from the upper uterus, the ovary, and the
upper part of the broad ligament is collected by several veins.
Within the broad ligament, these veins form the large pampi­
niform plexus that terminates in the ovarian vein. From here,
the right ovarian vein empties into the vena cava, whereas the
left ovarian vein empties into the left renal vein.
Ureter
Ovari a n a .
/
Inferior mesenteric a .
I l i ol u m ba r a .
Obturator a .
Accessory obturator a .
Su peri o r rectal a .
I n ferior epigastri c a .
Ro u n d l iga ment (cut)
Lateral sacra l a .
M ed i a l u m b i l i ca l l ig a ment
S u perior g l utea l a .
S u pe rior vesica l a a .
Inferior g l utea l a .
I n ferior vesical a .
Vag i n a l a .
I ntern a l pudendal a .
Uteri ne a .
(asce n d i n g bra n c h )
Sam pson a . t o rou n d l i g a ment
Uterus
Rou nd l iga ment ( cut)
F I G U R E 2-1 2 Pelvic a rteries. (Reprod uced with perm ission from Corton MM: Anatomy. In Hoffman BL, Schorge JO, Bradshaw KD, et a l (ed s):
Wi l l iams Gynecology, 3 rd ed . New York, McGraw- H i l i Ed ucation, 201 6.)
Mate r n a l A natomy
Blood supply to the pelvis is predominantly provided by
branches of the internal iliac artery (Fig. 2- 1 2) . These branches
are organized into anterior and posterior divisions, and sub­
sequent branches are highly variable between individuals. The
anterior division provides blood supply to the pelvic organs and
perineum and includes the inferior gluteal, internal pudendal,
middle rectal, vaginal, uterine, and obturator arteries, as well as
the umbilical artery and its continuation as the superior vesical
artery. The posterior division branches extend to the buttock
and thigh and include the superior gluteal, lateral sacral, and
iliolumbar arteries. For this reason, during internal iliac artery
ligation, many advocate ligation distal to the posterior division
to avoid compromised blood low to the areas supplied by this
division (Bleich, 2007) .
• Pelvic Lymphatics
The lymphatics from the uterine corpus are distributed to two
groups of nodes. One set of vessels drains into the internal iliac
nodes. The other set, after joining lymphatics from the ovarian
region, terminates in the paraaortic lymph nodes. Lymphatics
from the cervix terminate mainly in the internal iliac nodes,
which are situated near the bifurcation of the common iliac
vessels.
• Pelvic Innervation
As a brief review, the peripheral nevous system is divided into
a somatic division, which innervates skeletal muscle, and an
autonomic division, which innervates smooth muscle, cardiac
muscle, and glands. Pelvic visceral innervation is predomi­
nantly autonomic, which is further divided into sympathetic
and parasympathetic components.
Sympathetic innervation to pelvic viscera begins with the
superior hypogastric plexus, also termed the presacral nerve
(Fig. 2- 1 3 ) . Beginning below the aortic bifurcation and
extending downward retroperitoneally, this plexus is formed
by sympathetic fi b ers arising from spinal levels TID through
L2 • At the level of the sacral promontory, this superior hypo­
gastric plexus divides into a right and a left hypogastric nerve,
which run downward along the pelvis sidewalls (Ripperda,
20 1 5).
Pelvic s p l a n c h n i c neves
( n ervi erige ntes)
Su perior h ypog astri c
plexus ( p resacra l n e rve)
I n fe rior h ypog astric
( pelv ic) p lexu s
Right hypog astric n e rve
S acra l sym path etic
tru n k
Fifth sacra l n e rve
Vesica l plexus
I
•
�
Fibers to vesti b u l a r b u l bs
a n d cl i toriS
M id d le recta l p lexus
Uterova g i n a l plexus
( Fra n ke n h a u ser g a n g lion )
FIGURE 2- 1 3 Pelvic i n nervation. (Reprod uced with permission from Corton MM: Anatomy. In Hofman B L, Schorge JO, B radshaw KD, et al (eds):
Wi l l iams Gynecology, 3 rd ed. New York, McGraw- H i l i Ed ucation, 20 1 6.)
27
28
Maternal Anato m y a nd P hys i ology
In contrast, parasympathetic innervation to the pelvic vis­
cera derives from neurons at spinal levels 5 2 through 54' heir
axons exit as part of the anterior rami of the spinal nerves for
those levels. These combine on each side to form the pelvic
splanchnic nerves, also termed nervi erigentes.
Blending of the two hypogastric nerves (sympathetic) and
the two pelvic splanchnic nerves (parasympathetic) gives rise to
the inferior hypogastric plexus, also termed the pelvic plexus.
his retroperitoneal plaque of nerves lies at the 54 and 55 level
(Spackman, 2007) . From here, fibers of this plexus accompany
internal iliac artery branches to their respective pelvic viscera.
Thus, the inferior hypogastric plexus divides into three plex­
uses. he vesical plexus innervates the bladder, and the middle
rectal plexus travels to the rectum. he uterovaginal plexus,
also termed F rankenhauser plexus, reaches the proximal fallo­
pian tubes, uterus, and upper vagina. Extensions of the inferior
hypogastric plexus also reach the perineum along the vagina
and urethra to innervate the clitoris and vestibular bulbs (Mon­
toya, 20 1 1 ) . Of these, the uterovaginal plexus is composed of
variably sized ganglia, but particularly of a large ganglionic
plate that is situated on either side of the cervix, proximate to
the uterosacral and cardinal ligaments (Ramanah, 20 1 2) .
For the uterus, most o f its aferent sensory fibers ascend
through the inferior hypogastric plexus and enter the spinal
cord via T 10 through T 12 and L] spinal nerves. These transmit
the painful stimuli of contractions to the central nervous sys­
tem. For the cervix and upper part of the birth canal, sensory
nerves pass through the pelvic splanchnic nerves to the second,
third, and fourth sacral nerves. Last, those from the lower por­
tion of the birth canal pass primarily through the pudendal
nerve. Anesthetic blocks used during delivery target these levels
of innervation.
• Ovaries
long the pelvic sidewall, each ovary usually rests in the ovar­
ian fossa of Waldeyer, which is a slight depression between the
external and internal iliac vessels. During childbearing years,
ovaries variably measure 2.5 to 5 cm in length, 1 . 5 to 3 cm in
width, and 0.6 to 1 . 5 cm in thickness.
he ovarian ligament, also called the uteroovarian liga­
ment, originates from the upper posterolateral portion of the
uterus, just beneath the tubal insertion level, and extends to
the uterine pole of the ovary (see Fig. 2- 1 0) . Measuring a few
centimeters long and 3 to 4 mm in diameter, this ligament is
made up of muscle and connective tissue and is covered by
peritoneum-the mesovarium. Blood supply reaches the ovary
through this double-layered mesovarium to enter the ovarian
hilum.
The ovary consists of an outer cortex and inner medulla. In
young women, the cortex is smooth, has a dull white surface,
and is lined by single layer of cuboidal epithelium, the germi­
nal epithelium of Waldeyer. his epithelium is supported by a
connective tissue condensation, the tunica albuginea. Beneath
this, the ovarian cortex contains oocytes and developing fol­
licles. The medulla is composed of loose connective tissue,
numerous arteries and veins, and a small amount of smooth
muscle ibers.
The ovaries are supplied with both sympathetic and para­
sympathetic nerves. he sympathetic nerves are derived primar­
ily from the ovarian plexus that accompanies the ovarian vessels
and originates in the renal plexus. Others are derived from the
plexus that surrounds the ovarian branch of the uterine artery.
Parasympathetic input is from the vagus nerve. Sensory afer­
ents follow the ovarian artery and enter at T]o spinal cord level.
• Fallopian Tubes
Also called oviducts, these serpentine tubes extend laterlly 8 to
1 4 cm from the uterine cornua. hey are anatomically classified
along their length s an interstitial portion, isthmus, ampulla, and
inundibulum (Fig. 2- 14) . vIost proximal, the interstitial portion
is embodied within the uterine muscular wall. Next, the narrow
2- to 3-mm wide isthmus widens gradually into the 5- to 8-mm
wide ampulla. Last, the inundibulum is the unnel-shaped fim­
briated distal extremity of the tube, which opens into the abdomi­
nal cavity. These latter three extrauterine portions are covered by
the mesosalpinx at the superior margin of the broad ligament.
In cross section, the extrauterine fallopian tube contains a
mesosalpinx, myosalpinx, and endosalpinx. he outer of these,
the mesosalpinx, is a single-cell mesothelial layer unctioning
as visceral peritoneum. In the myosalpinx, smooth muscle is
arranged in an inner circular and an outer longitudinal layer. The
tubal musculature undergoes rhythmic contractions constantly,
the rate of which varies with cyclical ovarian hormonal changes.
The tubal mucosa or endosalpinx is a single layer of colum­
nar epithelium composed of ciliated, secretory, and intercalary
cells resting on a sparse lamina propria. Clinically, its close
proximity to the underlying myosalpinx contributes to easy
invasion by ectopic trophoblast. The tubal mucosa is arranged
in longitudinal folds that become progressively more complex
toward the fi m bria. In the ampulla, the lumen is occupied
almost completely by the arborescent mucosa. The current
produced by the tubal cilia is such that the direction of flow is
toward the uterine cavity. Tubal peristalsis created by cilia and
muscular layer contraction is believed to be an important factor
in ovum transport (Croxatto, 2002) .
he tubes are supplied richly with elastic tissue, blood ves­
sels, and lymphatics. Their sympathetic innervation is exten­
sive, in contrast to their parasympathetic innervation. This
nerve supply derives partly from the ovarian plexus and partly
from the uterovaginal plexus. Sensory aferent ibers ascend to
T]o spinal cord levels.
LOWER U RI NARY TRACT STRUCTURES
• Bladder
Anteriorly, the bladder rests against the inner surface of the
pubic bones and then, as it fills, also against the anterior
abdominal wall. Posteriorly, it rests against the vagina and cer­
vix. he bladder is divided into a dome and a base approxi­
mately at the level of the ureteral oriices. The dome is thin
walled and distensible, whereas the base is thicker and under­
goes less distention during filling. The vesical trigone lies in the
bladder base and contains both ureteral oriices and the internal
Maternal A n atomy
traverses through the cardinal ligament
approximately 1 to 2 cm lateral to the
cervix. Near the level of the uterine isth­
mus, it courses below the uterine artery
and travels anteromedially toward the
bladder base. In this path, it runs close
to the upper third of the anterior vaginal
wall (Rahn, 2007) . Finally, the ureter
enters the bladder and travels obliquely
for approximately 1 . 5 cm before open­
ing at the ureteral oriices.
The pelvic ureter receives blood sup­
ply from the vessels it passes: the common
iliac, internal iliac, uterine, and superior
vesical vessels. The ureter's course runs
medial to these vessels, and thus its blood
supply reaches the ureter from lateral
sources. This is important during ure­
teral isolation. Vascular anastomoses on
the connective tissue sheath enveloping
the ureter form a longitudinal nenvork of
vessels.
MUSCU LOSKELETAL PELVIC
ANATOMY
A
B
• Pelvic Bones
The pelvis is composed of four bones­
the sacrum, coccyx, and two innominate
bones. Each innominate bone is formed
by the fusion of three bones-the ilium,
ischium, and pubis (Fig. 2- 1 5) . Both
innominate bones are joined to the
sacrum at the sacroiliac synchondroses and to one another at
the symphysis pubis.
F I G U R E 2-1 4 The fa llopian tube of an ad u lt wom a n with cross-sectioned i l l u strations of
the g ross struct u re in severa l portions: (A) i sthmus, (B) a m p U l la, a n d (C) i n fu n d i b u l u m .
Below these a re photog ra phs o f corresponding h i stolog ica l sections. (U sed with permis­
sion from Dr. Kel ley S. Ca rrick.)
urinary meatus (see Fig. 2- 1 1 ) . he urethral lumen begins at
this meatus and then courses through the bladder base for less
than 1 cm. This region where the urethral lumen traverses the
bladder base is called the bladder neck.
The bladder wall consists of coarse bundles of smooth muscle
known as the detrusor muscle, which extends into the proximal
part of the urethra. A submucosal layer intervenes between this
detrusor muscle and the mucosa. he bladder mucosa consists
of transitional epithelium and underlying lamina propria.
The blood supply to the bladder arises from the superior
vesical arteries, which are branches of the patent portion of the
umbilical artery, and from the middle and inferior vesical arter­
ies, which, when present, often arise from either the internal
pudendal or the vaginal arteries (see Fig. 2- 1 2) . The nerve sup­
ply to the bladder arises from the vesical plexus, a component
of the inferior hypogastric plexus (see Fig. 2- 1 3) .
• Ureter
As the ureter enters the pelvis, it crosses over the bifurca­
tion of the common iliac artery and passes just medial to the
ovarian vessels (see F ig. 2- 1 0) . As the ureter descends into
the pelvis, it lies medial to the internal iliac branches and
anterolateral to the uterosacral ligaments. The ureter then
• Pelvic Joints
Anteriorly, the pelvic bones are joined together by the sym­
physis pubis. This structure consists of fibrocartilage and the
superior and inferior pubic ligaments. The latter ligament is
frequently designated the arcuate ligament of the pubis. Poste­
riorly, the pelvic bones are j oined by articulations between the
sacrum and the iliac portion of the innominate bones to form
the sacroiliac joints.
The pelvic joints in general have a limited degree of
mobility. However, during p regnancy, these joints relax
remarkably at term . As one result, upward gliding of the
sacroiliac j oint, which is greatest in the dorsal lithotomy
position, may increase the diameter of the outlet by 1 . 5 to
2 . 0 cm for delivery (Borell, 1 957) . Sacroiliac joint mobil­
ity also likely aids the McRoberts maneuver to release an
obstructed shoulder in cases of shoulder dystocia (Chap. 27,
p . 5 2 1 ) . These changes may also contribute to the success
of the modifi e d squatting position to hasten second-stage
labor (Cardosi , 1 9 89) . The squatting position may increase
the interspinous diameter and the pelvic outlet diameter
(Russell, 1 969, 1 982) .
29
30
Mate r n a l A n atomy a n d Physiol ogy
'
I
.
- - Promontory
''
/
i
.r
Greater sci atic foramen
Isch i a l spine
I
/
Sym physis
pubis
-
Sacrospinous ligament
- Lesser sciatic foramen
t- Sacrotu berous liga ment
fora men
cannot be measured directly with examin­
ing fingers. hus, the obstetrical conjugate
is estimated indirectly by subtracting 1 . 5
to 2 cm from the diagonal conjugate. To
measure the diagonal conjugate, a hand
with the palm oriented laterally extends
its index finger to the promontory. The
distance from the fingertip to the point at
which the lowest margin of the symphysis
strikes the same inger's base is the diagonal
conjugate.
he transverse diameter is constructed
at right angles to the obstetrical conju­
gate and represents the greatest distance
between the linea terminalis on either side
(see Fig. 2- 1 6) . It usually intersects the
obstetrical conjugate at a point approxi­
mately 5 cm in front of the promontory
and measures approximately 1 3 cm.
M i d pelvis a n d Pe lvic Outl et
The midpelvis is measured at the level of
F I G U R E 2-1 5 The i n nom i nate bone is com posed of the pubis (brown), i sch i u m (red), and
the ischial spines, also called the midplane
i l i u m (blue). Of the th ree a nteroposterior d i a m eters of the pelvic i n l et, o n ly the d iagona l
or plane of least pelvic dimensions (see
conj u g ate can be measu red c l i n ica l ly. The i m portant o bstetrical conj u g ate is derived by
Fig. 2- 1 6) . During labor, the degree of
s u btracti ng 1 5 cm from the d iagonal conj ug ate.
fetal head descent into the true pelvis may
be described by station, and the midpelvis
• Planes and Diameters of the Pelvis
and ischial spines serve to mark zero station. The interspinous
The pelvis is conceptually divided into false and true compo­
diameter is 10 cm or slightly greater and is usually the smallest
nents. The false pelvis lies above the linea terminalis, and the
pelvic diameter. The anteroposterior diameter through the level
true pelvis is below this boundary (Fig. 2- 1 6) . he false pelvis
of the ischial spines normally measures at least 1 1 .5 cm.
is bounded posteriorly by the lumbar vertebra and laterally by
The pelvic outlet consists of two approximately triangular
the iliac fossa. In front, the boundary is formed by the lower
areas whose boundaries mirror those of the perineal triangle
portion of the anterior abdominal wall.
described earlier (p. 1 9) . They have a common base, which
he pelvis is described as having four imaginary planes:
is a line drawn between the two ischial tuberosities. The apex
of the posterior triangle is the tip of the sacrum, and the
1 . The plane of the pelvic inlet-the superior strait.
2. The plane of the pelvic outlet-the inferior strait.
3. he plane of the midpelvis-the least pelvic dimensions.
4. he plane of greatest pelvic dimension-of no obstetrical
significance.
Pelvic I n l et
he pelvic inlet, also called the superior strait, is the superior
plane of the true pelvis. It is bounded posteriorly by the prom­
ontory and alae of the sacrum, laterally by the linea terminalis,
and anteriorly by the horizontal pubic rami and the symphysis
pubis. During labor, fetal head engagement is deined by the
fetal head's biparietal diameter passing through this plane.
Four diameters of the pelvic inlet are usually described:
anteroposterior, transverse, and two oblique diameters. Of these,
distinct anteroposterior diameters have been described using spe­
cific landmarks. Most cephalad, the anteroposterior diameter,
termed the true conjugate, extends from the uppermost margin
of the symphysis pubis to the sacral promontory (see Fig. 2- 1 5) .
h e clinically important obstetrical conjugate i s the shortest dis­
tance between the sacral promontory and the symphysis pubis.
Normally, this measures 10 cm or more, but unfortunately, it
-
�/
(/,
I
.Iium
.
i
F I G U R E 2-1 6 Axial view of a normal female pelvis. The cl i n ica l l y
i mportant obstetrica l conjugate a n d tra n sverse dia meter o f the
pelvic in let a re i l l ustrated. The i nterspinous dia meter of the mid pel­
vis is a lso ma rked.
Maternal Anatomy
Anthropotd
,
•
.
,
Intermediates
•
. . 4
Gynecoid
Android
PlatypellOid
FIGURE 2 - 1 7 The four parent pelvic types of the Caldwell-Moloy classification. A li ne passing through the widest transverse diameter
divides the inlets into posterior (P) and anterior (A) segments.
lateral boundaries are the sacrotuberous ligaments and the ischial
tuberosities. 'he anrerior triangle is formed by the descending
inferior rami of rhe pubic bones. These rami unite at an angle of
90
[0
100 degrees ro form a rounded arch under which the fetal
head must pass. Unless there is Signiicant pelvic bony disease,
rhe pelvic ourler seldom obstructs vaginal delivery.
• Pelvic Shapes
The Caldwell-Moloy ( I 933, 1 934) anaromical classiication of
rhe pelvis is based on shape, and its concepts aid an understand­
ing of labor mechanisms. Speciically, the grearesr transverse
diameter of rhe inler and its division into alHerior and posterior
segmelHs are used to classiy rhe pelvis as gynecoid, anthropoid,
android, or platypelloid. The posterior segmelH determines the
type of pelvis, whereas the anterior segment determines the ten­
dency. These are both determined because many pelves are nor
pure but are mixed types. For example, a gynecoid pelvis with
an android tendency means that rhe posterior pelvis is gynecoid
and the anterior pelvis is android shaped.
From viewing the four basic types in Figure 2- 1 7 , the
coniguration o f the gynecoid pelvis would intuitively seem
suited for delivery of most fetuses. Indeed, Caldwell ( I 939)
reported [hac rhe gynecoid pelvis was found in almost half
of women.
REFERENCES
Barher MD, Bremer E, Thor KB, er al: Innervation of the female levator ani
muscles. Am J Obsrer Gynecol 1 87:64, 2002
Beer GM, Schuster A, Seifert B, et al: 1he normal width of the linea alba in
nulliparous women. Clin Anar 22(6):706, 2009
Bleich AT, Rahn DO, Wieslander CK, et al: Posterior division of the inter­
nal iliac artery: anatomic variations and clinical applications. Am J Obstet
Gynecol 197:658.e1, 2007
Borell U, Fenstrom I: Movements at the sacroiliac joillls and their importance
to changes in pelvic dimensions during parturition. Acta Obstet Gynecol
Scand 36:42, 1957
Caldwell WE, 'vl oloy He: Anatomical variations in the female pelvis and their
efect in Jabor with a suggested classiication. Am J Obstet GynecoJ 26:479,
1933
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33
C H A PT E R 3
Co n g e n ita l G e n i to u ri n a ry
Ab n o rm a l i t i es
GEN ITOU R I NARY TRACT DEVELOPM ENT
SEXUAL DIFFERENTIATION . .
.
.
.
. . . . .
.
.
. . . . .
.
.
.
. .
.
33
. . . . . . . . . . . . . 38
DISORDERS OF SEX DEVELOPMENT. . . . .
.
.
.
.
.
. . .
.
.
.
. 38
BLADDER AND PERINEAL ABNORMALITI ES . . . . . . , . . . 41
M U LLERIAN ABNORMALITIES . . . .
.
. .
.
.
. . . . .
.
. . . . . . . 41
UTERINE F LEXION . . . . . . . . . , . . . . . . . . . . . . . . , . . , . . . 46
Abnormalities in the development or fusion of one or both
MUllerian ducts may result in maormations which some­
times possess an obstetrical signicance. Pregnancy may be
associated with any one ofthese maormations, provided an
ovum be cast ofrom the ovaries and no serious obstacle be
opposed to the upward passage of the spermatozoa and their
subsequent union with it.
- ]. Whitridge Williams ( 1 903)
GENITOURINARY TRACT DEVELOPMENT
In females, the external genitalia, gonads, and miillerian ducts
each derive from diferent primordia and in close association
with the urinary tract and hindgut. Abnormal embryogenesis
during this process is thought to be multifactorial and can cre­
ate sporadic anomalies. Several of these can lead to infertility,
subfertility, miscarriage, or preterm delivery. Thus, knowledge
of genitourinary system development is essential.
• Embryology of the Urinary System
Between the 3rd and 5th gestational weeks, an elevation ofinter­
mediate mesoderm on each side of the fetus-the urogenital
ridge-begins development into the urogenital tract. Sub­
sequently, the urogenital ridge divides into the genital ridge,
destined to become the ovary, and into the nephrogenic ridge
(Fig. 3- 1 ) , he nephrogenic ridges develop into the mesoneph­
ros (mesonephric kidney) and paired mesonephric ducts, also
termed wolian ducts, which connect to the cloaca.
The early urinary tract develops from the mesonephros and
its mesonephric ducts (Fig. 3-2A) . Recall that evolution of the
renal system passes sequentially through the pronephric and
mesonephric stages to reach the permanent metanephric sys­
tem. Between the 4th and 5th weeks, each mesonephric duct
gives rise to a ureteric bud, which grows cephalad toward its
respective mesonephros (Fig. 3-2B) , As each bud lengthens, it
induces diferentiation of the metanephros, which will become
the inal kidney (Fig. 3-2C) . Each mesonephros degenerates
near the end of the first trimester, and without testosterone,
the mesonephric ducts regress as well.
he cloaca begins as a common opening for the embry­
onic urinary, genital, and alimentary tracts. By the 7th week it
becomes divided by the urorectal septum to create the rectum
and the urogenital sinus (Fig. 3-2D) . The urogenital sinus is
considered in three parts: ( 1 ) the cephalad or vesicle portion,
which forms the urinary bladder; (2) the middle or pelvic por­
tion, which creates the female urethra; and (3) the caudal or
phallic part, which gives rise to the distal vagina and to the
greater vestibular (Bartholin) and paraurethral glands.
• Embryology of the Genital Tract
he fallopian tubes, uterus, and upper vagina derive from the
miillerian ducts, also termed paramesonephric ducts, which
form adjacent to each mesonephros (see Fig. 3-2B) . These
ducts extend downward and then turn medially to meet and
fuse together in the midline. he uterus is formed by this union
of the two miillerian ducts at approximately the 1 0th week
(Fig. 3-2E) . Fusion to create the uterus begins in the middle
and then extends both caudally and cephalad. With cellular
34
Materna l Anatomy a n d P hysiology
Dorsal root
ganglion
Nephrogenic
ridge
Paramesonephri
duct
Genital
ridge
Cloaca
F I G U RE 3-1 A. Cross-section of an embryo at 4 to 6 weeks. B. La rge a me boid pri mord i a l germ cel l s m i g rate (arrows) from the yolk sac to
the a rea of germinal epithel i u m, wit h i n the gen ita l ridge. C. M i g ration of sym pathetic cel l s from the s p i n a l g a n g l i a to a region a bove the
developing kid ney.
Mesonephros
Mesonephros
\ '
Mullerian
duct
�
Bladder
Alimentary tract
B
A
Urogenital
sinus o
�
Metanephric
�
\
U rorectal
duct
Rectum
septum
Bladder
/ I
Metanephros
/
/. (Kidney)
-
/
U reteric bud
and metanephros
Cloaca Alimentary tract
Urogenital
E
�
Mesoneph ric
duct
Mullerian duct
( Fallopian tube)
---Mullerian
�
" Rectum
Cloaca
c
Remnant of
mesonephric
duct
Fused
ducts
\
Alimentary tract
( Rectum)
Bladder
Metanephric duct
( U reter)
-
U rethra
F
/
--- U reter
1 -::
-..-Uterus
---Rectum
F IG U RE 3-2 Em bryonic develo pment of the female genitourinary tract (A- F). (Reprod uced with permission from Shatzkes DR, Ha ller JO,
Velcek FT: I ma g i ng of uterova g i n a l anoma lies in the ped iatric patient, U rol Rad iol 1 99 1 ; 1 3 ( 1 ) :58-66.)
Co ngen ita l G e n i to u r i n a ry A b norm a l i t ies
proliferation at the upper portion, a thick wedge of tissue cre­
ates the characteristic piriform uterine shape. At the same time,
dissolution of cells at the lower pole forms the irst uterine cav­
ity (Fig. 3-2F) . As the upper wedge-shaped septum is slowly
reabsorbed, the inal uterine cavity is usually formed by the
20th week. If the two mullerian ducts fail to fuse, then two
separate uterine horns remain. In contrast, resorption failure of
the common tissue between them results in various degrees of
persistent uterine septum.
As the distal end of the fused mullerian ducts contacts the uro­
genital sinus, this induces endodermal outgrowths from the sinus
termed the sinovaginal bulbs. hese bulbs proliferate and fuse
to form the vaginal plate, which later resorbs to form the vaginal
lumen. his vaginal canalization is generally completed by the
20th week. However, the lumen remains separated from the
urogenital sinus by the hymeneal membrane. This membrane
further degenerates to leave only the hymeneal ring.
The close association of the mesonephric (wolian) and
paramesonephric (mullerian) ducts explains the simultane­
ous abnormalities in their end organs. Kenney and colleagues
( 1 984) showed that up to half of females with urerovaginal
malformations have associated urinary tract defects. Anomalies
most frequently associated with renal defects are unicornuate
uterus, uterine didelphys, and agenesis syndromes, whereas
arcuate and bicornuate are less commonly linked (Reichman,
20 1 0) . When mullerian anomalies are identiied, the urinary
system can be evaluated with magnetic resonance (MR) imag­
ing, sonography, or intravenous pyelography (Hall-Craggs,
20 1 3) . With mullerian anomalies, ovaries are functionally nor­
mal but have a higher incidence of anatomical maldescent into
the pelvis (Allen, 20 1 2; Dabirashrafi, 1 994) .
As discussed, the mesonephric ducts usually degenerate,
however, persistent remnants may become clinically apparent.
Mesonephric or wolian vestiges can persist as Gartner duct
cysts. These are typically located in the proximal anterolateral
vaginal wall but may be found at other sites along the vagi­
nal length. They can be further characterized by MR imaging,
which provides excellent image resolution at soft tissue inter­
faces. Most cysts are asymptomatic and benign and usually do
not require surgical excision.
Intraabdominal wolian remnants in the female include
a few blind tubules in the mesovarium-the epoophoron­
and similar ones adjacent to the uterus-paroophoron (see
Fig. 3-2F) (Moore, 20 1 3) . The epoophoron or paroophoron
may develop into clinically identiiable cysts in the adult.
• Embryology of the Gonads
At approximately 4 weeks, gonads derive from coelomic epithe­
lium covering the medial and ventral surface of the nephrogenic
cord at a site between the eighth thoracic and fourth lumbar
segments. Because of this separate gonadal and mullerian deri­
vation, women with mullerian defects typically have function­
ally normal ovaries and are phenotypic females. he coelomic
epithelium thickens to form the genital ridge, also known as the
gonadal ridge. Strands of these epithelial cells extend into the
underlying mesenchyme as the primary sex cords. By the sixth
week, primordial germ cells have migrated from the yolk sac to
enter the genital ridge mesenchyme (Fig. 3-3 ) . The primordial
germ cells are then incorporated into the primary sex cords.
In the seventh week, the sexes can be distinguished, and tes­
tes are recognized during microscopic sectioning by their well­
deined radiating testis cords. These cords are separated from
the coelomic epithelium by mesenchyme that is to become the
tunica albuginea. The testis cords develop into the seminiferous
tubules and rete testis. he rete testis establishes connection
with small tubes arising of the mesonephric duct. These small
tubes become the eferent ducts that drain into the epididymis
and then into the vas deferens, which are main mesonephric
duct derivatives.
In the female embryo, the primary sex cords give rise to
the medullary cords, which persist only for a short time. The
coelomic epithelium again proliferates into the underlying mes­
enchyme, and these strands are the cortical cords. By the fourth
month, the cortical cords begin to form isolated cell clusters
called primordial follicles. These follicles contain the oogonia,
which derive from primordial germ cells and are surrounded
by a single layer of lattened follicular cells derived from the
cortical cords. Follicular cells serve as supporting nutrient cells.
By 8 months, the ovary has become a long, narrow, lobulated
structure that is attached to the body wall by the mesovarium.
The coelomic epithelium has been separated by a band of con­
nective tissue-tunica albuginea-from the cortex. At this
stage, the cortex contains follicles and is well deined from the
inner medulla, which is composed of abundant blood vessels,
lymphatic vessels, and nerve ibers.
• Embryology of the External Genitalia
Early development of the external genitalia is similar in both
sexes. By 6 weeks' gestation, three external protuberances have
developed surrounding the cloacal membrane. These are the left
and right cloacal folds, which meet ventrally to form the geni­
tal tubercle (Fig. 3-4) . With division of the cloacal membrane
into anal and urogenital membranes, the cloacal folds become
the anal and urethral folds, respectively. Lateral to the urethral
folds, genital swellings arise, and these become the labioscrotal
folds. Between the urethral folds, the urogenital sinus extends
onto the surface of the enlarging genital tubercle to form the
urethral groove. By week 7, the urogenital membrane ruptures,
exposing the cavity of the urogenital sinus to amnionic fluid.
The genital tubercle elongates to form the phallus in males
and the clitoris in females. Still, it is not possible to visually
diferentiate between male and female external genitalia until
week 1 2. In the male fetus, dihydrotestosterone (DHT) forms
locally by the 5-a reduction of testosterone. D HT prompts the
anogenital distance to lengthen, the phallus to enlarge, and the
labioscrotal folds to fuse and form the scrotum.
In the female fetus, without DHT, the anogenital distance
does not lengthen, and the labioscrotal and urethral folds do not
fuse (Fig. 3-4C) . The genital tubercle bends caudally to become
the clitoris, and the urogenital sinus forms the vestibule of the
vagina. The labioscrotal folds create the labia majora, whereas
the urethral folds persist as the labia minora. Female external
genital diferentiation is complete by 1 1 weeks, whereas male
external genital diferentiation is complete by 14 weeks.
35
36
Mate r n a l A nato my a n d Phys i o l ogy
Paramesoneph ric
duct
Mesoneph ric
duct
Paramesonephric -!­
duct
TDF
No TDF
Degenerating paramesonephric duct
Persistent para­
mesonephric duct
Coelomic epithelium
Degenerating
medullary cords
Uterine
tube
P rimordial germ cel l
FIGURE 3-3 Embryon ic gonad d iferentiation . TDF
=
testis-d eterm i n i n g factor.
Co n g e n ita l Genito u ri n a ry Abnorm a l ities
Gen ital
tUbercle
Ind ifferent stages
�
U roge n ital
membrane
U rethral
fold
�
U rogenital
membrane
breaks down
--
Cloacal
fold
Labioscrotal
swelling --
C loacal -­
membrane
Anal -�·membrane
A
___Perine u m
---
Anal fold
Late 7th week
Early 7th week
6th week
Differentiation
Male
B
U rethral
g roove
C
�
!
--"-U rethral
groove
G lans penis
Genital
tU bercle
P rimitive u rogen ital
o rifice
Scrotum
Gen ital
raphe
Anus
�
U reth ral
g roove
U reth ral
fold
Labioscrotal
folds
!
/
Perineum
, ..---- Anus
FIGURE 3-4 Development of the extern a l gen ita l ia. A. Ind ifferent stage. B. Vi ri lization of extern a l genita l ia. C. Fem i n ization. (Reprod uced
with permission from Bradshaw KD: Anatomica l disorders. In Hoffma n B L, Schorge JO, B radshaw KD, et a l (eds): Wi l l i a m s Gynecology, 3 rd ed.
New York, McGraw H i l l Education, 20 1 6.)
37
38
Mate r n a l A natomy a nd Physiol ogy
S EXUAL DIFFERENTIATION
Defining gender incorporates genetic gender, gonadal gen­
der, and phenotypic gender. Genetic gender-X or Y-is
established at fertilization. However, for the irst 6 weeks,
development of male and female embf) os is morphologically
indistinguishable.
Gonadal gender is heralded by the diferentiation of the pri­
mordial gonad into a testis or an ovary. If a Y chromosome is
present, the gonad begins developing into a testis. Testis devel­
opment is directed by a protein called the testis-determiningac­
tor (TDF), which modulates the transcription of several genes
involved in gonadal diferentiation. TDF is encoded by the sex­
determining region (SR) gene, located on the short arm of the
Y chromosome. But testis development is much more complex
and requires other autosomal genes (Nistal, 2 0 1 5a) .
he importance of the SRYgene i s demonstrated i n severl par­
adoxical conditions. First, 46,X phenotypic males can result from
translocation of the Y chromosome fragment containing SRY to
the X chromosome during meiosis of male germ cells Wu, 20 1 4) .
Similarly, 46,Y individuals can appear phenotypically female if
they carry a mutation in the SRY gene (Helszer, 20 1 3).
Last, phenoypic gender begins at 8 weeks' gestation. Before
this, urogenital tract development in both sexes is indistin­
guishable. Thereafter, diferentiation of the internal and exter­
nal genitalia to the male phenotype is dependent on testicular
function. In the absence of a testis, female diferentiation ensues
irrespective of genetic gender (Table 3- 1 ) .
In males, the fetal testis secretes a protein called mullerian­
inhibiting substance (MIS) , also called antimullerian hormone
(AM H) . It acts locally as a paracrine factor to cause mullerian
duct regression. Thus, it prevents the development of uterus,
fallopian tube, and upper vagina. AMH is produced by the Ser­
toli cells of the seminiferous tubules. Importantly, these tubules
appear in fetal gonads and secrete AMH before diferentiation
of Leydig cells, which are the cellular site of testosterone syn­
thesis. AMH is secreted as early as 7 weeks, and mullerian duct
regression is completed by 9 to 1 0 weeks. Because AMH acts
locally near its site of formation, if a testis were absent on one
side, the mullerian duct on that side would persist, and the
uterus and fallopian tube would develop on that side.
Apparently through stimulation initially by human chori­
onic gonadotropin (hCG), and later by fetal pituitary lutein­
izing hormone (LH), the fetal testes secrete testosterone. his
hormone acts directly on the wolian duct to efect the devel­
opment of the vas deferens, epididymis, and seminal vesicles.
Testosterone also enters fetal blood and acts on the external
genitalia anlage. In these tissues, testosterone is converted to
5a-DHT to cause virilization of the external genitalia.
DISORDERS OF SEX DEVELOPMENT
• Definitions
As evident from the prior discussion, abnormal sex develop­
ment may involve the gonads, internal duct system, or external
genitalia. Rates vary and approximate 1 in every 1 000 to 4500
births (Murphy, 20 1 1 ; Ocal, 20 1 1 ) . The nomenclature used
to describe disorders of sex development (DSDs) has evolved.
Current classiication of these disorders include: ( 1 ) sex chro­
mosome DSDs, (2) 46,Y DSDs, and (3) 46,X DSDs
(Table 3-2) (Hughes, 2006) .
Other important terms describe the abnormal phenotypic
findings that can be found. First, some disorders of sexual devel­
opment are associated with abnormal, underdeveloped gonads,
that is, gonadal dysgenesis. With this, if a testis is poorly formed,
it is called a dysgenetic testis, and if an ovary is poorly formed, it
is called a streak gona. In afected patients, the underdeveloped
gonad ultimately fails, which is indicated by elevated gonado­
tropin levels. Another important clinical sequela is that patients
bearing a Y chromosome are at high risk of developing a germ
cell tumor in the dysgenetic gonad.
A second term, ambiguous genitalia, describes genitalia that
do not appear clearly male or female. Abnormalities may include
TABLE 3-1 . Em bryo n i c U rogen ital Structu res a nd The i r Ad u lt Homolog ues
Ind iferent Structure
Female
Male
Gen ita l ridge
Pri m o rd i a l germ ce l l s
Sex cords
G u bernac u l u m
Mesonephric t u b u les
Mesoneph ric d ucts
Ova ry
Ova
G ra n u l osa cel l s
Ute roova rian a n d rou nd l i g a m ents
E poophoron, pa roop h o ro n
Gartner d uct
Para m esoneph ric d ucts
U roge n ita l s i n u s
Uterus, fa l lo p i a n tu bes, u pper vag i n a
Bladder, u reth ra
Vag i n a
Para u reth ral g l a n d s
G reate r (Ba rthol i n) a n d l esser
vest i b u l a r g l a n d s
C l itoris
La b i a m i n ora
La b i a majora
Testis
Spermatozoa
Sem i n iferous t u b u les, Sertol i cel l s
Gu bernacu l u m testi s
Efferent d uctu les, parad idym is
Epid idymis, d u ctu s defe re n s,
ejacu lato ry d uct
Pr ostatic utricle, a ppe n d i x of testis
Bladder, u reth ra
Prostatic utri cle
Prostate g l a n d s
B u l bo u ret h ra l g l a nd s
Gen ita l tu berc l e
U rogen ita l fo l d s
La b ioscrota l swel l i ngs
G l a n s pen i s
F l oor o f pe n i l e u reth ra
Scrot u m
Congen ita l Genito u r i n a ry Abnorma l ities
TABLE 3-2. Disorders of Sex Development (DSD)
Cla ssification
Sex Chromosome DSD
45,X Tu rnerd
47,xXY Kl i n efe lterd
45,X/46,XY Mixed g o n a d a l dysg e nesis
46,XX/46,XY Ovotesti c u l a r DSD
46,XY DSD
Testic u l a r development
P u re gonad a l dysgenesis
Partia l gonad a l dysgenesis
Ovotesti c u l a r
Testis reg ression
And rogen prod uction o r action
And rogen synthesis
Androgen receptor
LH/hCG rece ptor
AMH
46,XX DSD
Ova ry deve lopment
Ovotestic u l a r
Testi c u l a r
G o n a d a l dysg e nesis
A n d rogen excess
Feta l
Maternal
P l acenta l
C h ro m osoma l Ovotest icu l a r D S D
aAnd synd ro me va ria nts.
AMH
a nt i m u l lerian h or m o n e; h CG
h u ma n chori o n ic
g o nadotro p i n ; LH
l u tei n izi n g hormone.
Ada pted with perm ission from H u g hes lA, H o u k C, A h m ed
S F, et a l : Consensus statem e nt on management of i ntersex
d i so rders. j Ped iatr U ro l 2: 1 48, 2006.
=
Turner and linefelter syndromes are most frequently encoun­
tered (Nielsen, 1 990) .
Turner syndrome is caused by de novo loss or severe s truc­
tural abnormality of one X chromosome in a phenotypic
female. Most afected fetuses are spontaneously aborted. How­
ever, in girls with Turner syndrome who survive, pheno type
varies widely, bur nearly all afected patients have short stat­
ure. Associated problems include cardiac anomalies (especially
coarctation of the aorta) , renal anomalies, hearing impairment,
otitis media and mastoiditis, and an increased incidence of
hypertension, achlorhydria, diabetes mellirus, and Hashimoto
thyroiditis. It is the most common form of gonadal dysgenesis
that leads to primary ovarian failure. In these cases, the uterus
and vagina are normal and capable of responding to exogenous
hormones (Matthews, 20 1 7) .
Another sex chromosome disorder i s Klineelter syndrome
(47,Y) . hese individuals tend to be tall, undervirilized
males with gynecomastia and small, firm testes. They have sig­
nificantly reduced fertility from hypogonadism due to gradual
testicular cell failure. These men are at increased risk for germ
cell rumors, osteoporosis, hypothyroidism, diabetes mellirus,
breast cancer, cardiovascular abnormalities, and cognitive and
psychosocial problems (Aksglaede, 20 1 3; Calogero, 20 1 7) .
=
=
hypospadias, undescended testes, micropenis or enlarged clito­
ris, labial fusion, and labial mass.
Last, ovotesticular deines states characterized by ovarian and
testicular tissue in the same individual. It was formerly termed
true hermaphroditism. In these cases, diferent types of gonads
can be paired. he types of gonads that may be paired include a
normal testis, a normal ovary, a streak gonad, dysgenetic testis,
or an ovotestis. In the latter, both ovarian and testicular ele­
ments are combined within the same gonad. With ovotesticu­
lar DSDs, the internal ductal system structure depends on the
ipsilateral gonad and its degree of determination. Speciically,
the amount of AMH and testosterone determines the degree to
which the internal ductal system is masculinized or feminized.
Extenal genitalia are usually ambiguous and undermasculinized
due to inadequate testosterone.
• Sex Chromosome Disorders of Sex
Development
Tu rner a n d Kl i n efelter Synd ro m es
Sex chromosome disorders of sexual development typically
arise from an abnormal number of sex chromosomes. Of these,
Several karyotypes can create a coexistent ovary and testis, and
thus ovotesticular DSD is found in all three DSD categories
(see Table 3-2) . In the sex chromosome group, ovotesticular
DSD may arise from a 46,XX/46,XY karyotype. Here, an
ovary, testis, or ovotestis may be paired. he phenotype in gen­
eral mirrors that for ovotesticular disorders, which are described
earlier on this page.
For others in the sex chromosome DSD group, ovotesticular
disorder arises from a chromosomal mosaic such as 45,Xl46,XY.
With this karyotype, a picture of mixedgonadal dysgenesis shows
a streak gonad on one side and a dysgenetic or normal testis on
the other. The phenotypical appearance ranges from underviril­
ized male to ambiguous genitalia to Turner stigmata.
• 46,XY Disorders of Sex Development
Insuicient androgen exposure of a ferus destined to be a male
leads to 46,XY DSD-formerly called male pseudohermaph­
roditism. he karyotype is 46,XY and testes are frequently
present. he uterus is generally absent as a result of normal
embryonic AMH production by Sertoli cells. hese subjects are
most often sterile from abnormal spermatogenesis and have a
small phallus that is inadequate for sexual function. As seen in
Table 3-2, etiology of 46,XY DSD may stem from abnormal
testis development or from abnormal androgen productio n or
action.
46,XY Gonadal Dysgenesis
his spectrum of abnormal gonad underdevelopment includes
pure or complete, partial, or mixed 46,XY gonadal dysgenesis.
These are deined by the amount of normal testicular tissue and
by karyotype. Because of the potential for germ cell rumors
in dysgeneric testes and intraabdominal testes, afected patients
39
40
Maternal A nato my a n d P hysio l ogy
routinely have been advised to undergo gonadectomy Giang,
20 1 6) .
O f these, pure gonadal dysgenesis results from a mutation
in the SRY gene or in other genes with testis-determining
efects (Hutson, 20 1 4) . his leads to underdeveloped dysge­
netic gonads that fail to produce androgens or AMH . Formerly
named Swyer syndrome, the condition creates a normal prepu­
bertal female phenotype and a normal miillerian system due to
absent AMH .
Partialgonaal dysgenesis deines those with gonad development
intermediate between normal and dysgenetic testes. Depending
on the percentage of underdeveloped testis, wolian and miille­
rian structures and genital ambiguity are variably expressed.
Mixed gonadal dysgenesis is one type of ovotesticular dis­
order of sexual diferentiation. As discussed on page 39, one
gonad is streak, and the other is a normal or a dysgenetic tes­
tis. Of afected individuals, 1 5 percent have a 46,Y karyotype
(Nistal, 20 1 5 b) . The phenotype is wide ranging as with partial
gonadal dysgenesis.
Last, testicular regression can follow initial testis develop­
ment. A broad phenotypic spectrum is possible and depends
on the timing of testis failure.
A bnorma l A n d roge n Prod uction or Action
In some cases, 46,Y disorders of sexual diferentiation stem
from abnormalities in: ( 1 ) testosterone biosynthesis, (2) LH
receptor function, (3) AMH function, or (4) androgen recep­
tor action. First, the sex steroid biosynthesis pathway can sufer
enzymatic defects that block testosterone production. Depend­
ing on the timing and degree of blockade, undervirilized males
or phenotypic females may result. In contrast to these central
enzymatic defects, peripheral defects may be causative. Namely,
abnormal 5-. reductase type 2 enzyme action leads to impaired
conversion of testosterone to DHT and thus to undervirilization.
Second, hCG/LH receptor abnormalities within the testes
can lead to Leydig cell aplasia/hypoplasia and impaired testos­
terone production. In contrast, disorders of MH and AMH
receptors result in persistent miillerian duct syndrome (PMDS) .
Afected patients appear as males but have a persistent uterus
and fallopian tubes due to failed AMH action.
Last, the androgen receptor may be defective and result in
androgen-insensitivity syndrome (AIS). Resistance to andro­
gens may be incomplete and associated with varying degrees
of virilization and genital ambiguity. Milder forms have been
described in men with severe male factor infertility and poor
virilization.
Females with complete androgen-insensitivity syndrome
(CAIS) appear as phenotypically normal females at birth. They
often present at puberty with primary amenorrhea. External
genitalia appear normal; scant or absent pubic and axillary hair
are noted; the vagina is shortened or blind ending; and the
uterus and fallopian tubes are absent. However, these individu­
als develop breasts during pubertal maturation due to abundant
androgen to estrogen conversion. Testes may be palpable in
the labia or inguinal area or may be found intraabdominally.
Surgical excision of the testes after puberty is recommended to
decrease the associated risk of germ cell tumors, which may be
as high as 20 to 30 percent.
• 46,XX Disorders of Sex Development
As seen in Table 3-2, etiology of 46,X disorders of sexual dif­
ferentiation may stem from abnormal ovarian development or
from excess androgen exposure.
A b norma l Ova ria n Deve l opment
Disorders of ovarian development of those with a 46,X com­
plement include: ( 1 ) gonadal dysgenesis, (2) testicular DSD,
and (3) ovotesticular DSD.
With 4,X gonadal dysgenesis, similar to Turner syndrome,
streak gonads develop. These lead to hypogonadism, prepuber­
tal normal female genitalia, and normal miillerian structures,
but other Turner stigmata are absent.
With 4,X testicuar DSD, several possible genetic mutations
lead to testis-like formation within the ovary-streak gonad, dys­
genetic testis, or ovotestis. Defects may stem from SRY trans­
location onto one X chromosome. In individuals without SRY
translocation, other genes with testis-determining efects are most
likely activated. Regardless, production of MH prompts miil­
lerian system regression, and androgens promote wolian system
development and external genitalia masculinization. Spermato­
genesis, however, is absent due to a lack of needed genes on the
long arm of the Y chromosome. hese individuals are not usually
diagnosed until puberty or during infertility evaluation.
With 4,X ovotesticular DSD, individuals possess a uni­
lateral ovotestis with a contralateral ovary or testis, or bilateral
ovotestes. Phenotypic indings depend on the degree of andro­
gen exposures and mirror those for other ovotesticular DSDs
discussed on page 39.
A n d rogen Excess
Discordance between gonadal sex (46,X) and the phenotypic
appearance of external genitalia (masculinized) may also result
from excessive fetal androgen exposure. his was previously
termed female pseudohermaphroditism. In afected individu­
als, the ovaries and female internal ductal structures such as the
uterus, cervix, and upper vagina are present. hus, patients are
potentially fertile. he external genitalia, however, are viril­
ized to a varying degree depending on the amount and timing
of androgen exposure. he three embryonic structures that
are commonly afected by elevated androgen levels or ovarian
development disorders are the clitoris, labioscrotal folds, and
urogenital sinus. As a result, virilization may range from mod­
est clitoromegaly to posterior labial fusion and development
of a phallus with a penile urethra. Degrees of virilization can
be described by the Prader score, which ranges from 0 for a
normal-appearing female to 5 for a normal, virilized male.
Fetal, placental, or maternal sources can provide the exces­
sive androgen levels. Maternally derived androgen excess may
come from virilizing ovarian tumors such as luteoma and
Sertoli-Leydig cell tumor or from virilizing adrenal tumors.
Fortunately, these neoplasms infrequently cause fetal efects
because of the tremendous ability of placental syncytiotropho­
blast to convert C19 steroids-androstenedione and testoster­
one-to estradiol via the enzyme aromatase (Chap. 5, p. 1 03) .
As another source, drugs such as testosterone, danazol, and
other androgen derivatives may cause fetal virilization.
Co n g e n ita l Gen ito u ri n a ry Abnorm a l ities
Of fetal sources, exposure can arise from fetal congenital
adrenal hyperplasia (CAH) . his stems from a fetal enzyme dei­
ciency in the steroidogenic pathway that leads to androgen accu­
mulation. The most common defect is 2 1 -hydroxylase deiciency.
CAH is a frequent cause of virilization and has an incidence
approximating 1 in 1 0,000 to 20,000 live births (Speiser, 20 1 0) .
With CAH, phenotypes depend o n the location o f the enzyme
defect in the steroidogenic pathway and on the severity of the
resulting enzymatic deiciency (Miller, 201 1 ) . With severe enzy­
matic deiciency, afected newborns have life-threatening salt
wasting and virilization. Other mutations may prompt virilization
alone (Auchus, 20 1 5) . he mildest abnormalities present later and
are described as "nonclassic," "late-onset," or "adult-onset" CAH.
In these patients, activation of the adrenal axis at puberty increases
steroidogenesis and unmasks a mild enzymatic deficiency. Excess
androgen provides negative feedback to gonadotropin-releasing
hormone (GnRH) receptors in the hypothalamus. These patients
oten present with hirsutism, acne, and anovulation. Thus, late­
onset CAH may mimic polycystic ovarian syndrome (McCann­
Crosby, 20 1 4) . In some instances, CAH can be diagnosed
antenatally. Early maternal dexamethasone therapy can dampen
androgen excess to minimize virilization (Chap. 1 6, p. 3 1 7) .
O f rare placental sources, placental aromatase deiciency
from a fetal CP19 gene mutation causes an accumulation of
placental androgen and underproduction of placental estro­
gens (Chap. 5, p. 1 05) Gones, 2007) . Consequently, both the
mother and the 46,X fetus are virilized.
• Gender Assignment
Delivery of a newborn with a disorder of sexual diferentiation
is a potential medical emergency and can create possible long­
lasting psychosexual and social ramiications for the individual
and family. Ideally, as soon as the afected neonate is stable, par­
ents are encouraged to hold the child. he newborn is referred to
as "your baby," and suggested terms include "phallus," "gonads,"
"folds," and "urogenital sinus" to reference underdeveloped
structures. The obstetrician explains that the genitalia are incom­
pletely formed and emphasizes the seriousness of the situation
and the need for rapid consultation and laboratory testing.
Because similar or identical phenotypes may have several eti­
ologies, identiication of a speciic DSD may require several diag­
nostic tools (McCann-Crosby, 20 1 5) . Relevant neonatal physicl
examination evaluates: ( 1 ) ability to palpate gonads in the labio­
scrotal or inguinal regions, (2) ability to palpate uterus during rec­
tl examination, (3) phallus size, (4) genitalia pigmentation, and
(5) presence of other syndromic features. The newborn metabolic
condition is assessed, as hyperkalemia, hyponatremia, and hypo­
glycemia may indicate CAH. he mother is examined for signs of
hyperandrogenism. Other neonatal tests include genetic studies,
hormone measurements, imaging, and in some cases endoscopic,
laparoscopic, and gonadal biopsy. Sonography shows the presence
or absence of miillerian/wolian structures, n locate the gonads,
and can identiy associated mlformations such as renal anomalies.
BLADDER AND PERI N EAL ABNORMALITIES
Very early during embryo formation, a bilaminar cloacal mem­
brane lies at the caudal end of the germinal disc and forms
the infraumbilical abdominal wall. Normally, an ingrowth of
mesoderm between the ectodermal and endodermal layers of
the cloacal membrane leads to formation of the lower abdomi­
nal musculature and pelvic bones. Without this reinforcement,
the cloacal membrane may prematurely rupture, and depend­
ing on the extent of the infraumbilical defect, cloacal exstrophy,
bladder exstrophy, or epispadias may result.
Of these, cloacal exstrophy is rare. It includes the triad of
omphalocele, bladder exstrophy, and imperforate anus.
Bladder exstrophy is uncommon and is characterized by an
exposed bladder lying outside the abdomen. Associated ind­
ings often include abnormal external genitalia and a widened
symphysis pubis. At the same time, however, the uterus, fal­
lopian tubes, and ovaries are typically normal except for o cca­
sional miillerian duct fusion defects. Pregnancy with bladder
exstrophy is associated with greater risk for antepartum
pyelonephritis, urinary retention, ureteral obstruction, pelvic
organ prolapse, preterm birth, and breech presentation. The
American Urological Association has published management
guidelines for pregnancy (Eswara, 20 1 6) . Due to the exten­
sive adhesions from prior repair and altered anatomy typically
encountered, some recommend planned cesarean delivery at
a tertiary center (Deans, 20 1 2; Dy, 20 1 5 ; G reenwell, 2003) .
Epispadias without bladder exstrophy is rare and develops in
association with other anomalies such as a widened, patulous
urethra; absent or bifi d clitoris; nonfused labial folds; and lat­
tened mons pubis. Vertebral abnormalities and pubic symphy­
sis diathesis are also common .
Clitoral anomalies are unusual. One is clitoral duplication
or biid clitoris, which is rare and usually develops in associa­
tion with bladder exstrophy or epispadias. With female phallic
urethra, the urethra opens at the clitoral tip. Last, clitoromegaly
noted at birth suggests fetal exposure to excessive androgens
(p. 40) . In other cases, congenital clitoromegaly in females
born extremely premature is a rare but well-recognized finding
thought to be due to transient androgen levels in these neonates
(Greaves, 2008) .
As noted, the hymen marks the embryological boundary
between structures derived from the miillerian and urogenital
sinus. Hymeneal anomalies include imperforate, microperfo­
rate, cribriform (sievelike) , navicular (boat-shaped) , and sep­
tate hymens. They result from failure of the inferior end of the
vaginal plate-the hymeneal membrane-to canalize. Their
incidences approximate 1 in 1 000 to 2000 females (Ameri­
can College of Obstetricians and Gynecologists, 20 1 6) . D ur­
ing the neonatal period, signiicant amounts of mucus can
be secreted due to maternal estrogen stimulation. With an
imperforate hymen, secretions collect to form a bulging,
translucent yellow-gray mass, termed hydro- or mucocolpos,
at the vaginal introitus. Most are asymptomatic and resolve as
mucus is reabsorbed and estrogen levels decrease, b ut rarely
can cause perinatal urinary retention from their mass efects
Gohal , 2009).
M U LLERIAN ABNORMALITIES
Four principal deformities arise from defective miillerian duct
embryological steps: ( 1 ) agenesis of both ducts, either focally
41
42
Matern a l A natomy a n d Physiology
or along the entire duct length; (2) unilateral maturation of
one mullerian duct with incomplete or absent development of
the opposite side; (3) absent or faulty midline fusion of the
ducts; or (4) defective canalization. Various classifications have
been proposed, and Table 3-3 shows the one from the Ameri­
can Fertility Society ( 1 988). It separates anomalies into groups
with similar clinical characteristics, prognosis for pregnancy,
and treatment. It also includes one for abnormalities associ­
ated with fetal exposure to diethylstilbestrol (DES) . Several
other classiication systems have been crafted, but this one is
the most widely used (Acien, 20 1 1 ; Di Spiezio Sardo, 20 1 5 ;
Oppelt, 2005).
M ullerian anomalies may be suspected by symptoms or
physical findings such as vaginal septa, blind-ending vagina, or
duplicated cevix. Amenorrhea may be an initial complaint for
those with agenesis of a mullerian component. In those with
outlet obstruction, pelvic pain from occult blood that accu­
mulates and distends the vagina, uterus, or fallopian tubes may
arise from functioning endometrium. Endometriosis and its
associated dysmenorrhea, dyspareunia, and chronic pain are
also frequent with outlet obstruction.
• Mullerian Agenesis
Class I segmental defects are caused by mullerian hypopla­
sia or agenesis as shown in Figure 3-5. These developmen­
tal defects can afect the vagina, cervix, uterus, or fallopian
tubes and may be isolated or may coexist with other mullerian
defects.
TABLE 3-3. Classifi cation of M U "e r i a n Anoma l ies
I . Seg menta l mul lerian hypoplasia or agenesis
a. Vag i n a l
b. Cervica l
c. U te r i n e fu nda l
d. Tu b a l
e. C o m b i n ed a n o m a l ies
II. Unicorn uate uterus
a. Com m u n icat i n g rud i me nt a ry h o r n
b. N o n co m m u n icat i n g h o r n
c. N o endometrial cavity
d. No rud i m enta ry horn
I I I . Uteri ne d idelphys
IV. Bicornu ate uterus
a. Co m pl ete-d ivi sion to i nter n a l os
b. Pa rti a l
V. Septate uterus
a. Com plete-sept u m to i nter n a l os
b. Pa rti a l
VI. Arcuate
VI I . Diethylstil bestrol related
Data fro m American Fert i l ity Society: Th e A m e rica n Ferti l ity
Society class ifications of ad nexal a d h es i o n s, d i sta l t u b a l
occl U S i o n , t u ba l occl u s i on seconda ry to t u ba l l i gation,
tu ba l p reg n a nc i es, M u l lerian a n o m a l ies and i nt ra uteri n e
ad hesions, Fert i l Ste r i l 1 988 J u n;49(6) :944-955 .
• Vaginal Abnormalities
Of all vaginal anomalies, vaginal agenesis is the most profound
and may be isolated or associated with other mullerian anoma­
lies. One example is the Mayer-Rokitansky-Kuster-Hauser
(MRKH) syndrome, in which upper vaginal agenesis is typi­
cally associated with uterine hypoplasia or agenesis. Less often,
this syndrome also displays abnormalities of the renal, skeletal,
and auditory systems. his triad is known by the acronym
MURCS, which reflects mullerian duct aplasia, renal aplasia,
and �ervicothoracic �omite dysplasia (Rall, 20 1 5) .
h e obstetrical significance o f vaginal anomalies depends
greatly on the degree of obstruction. Complete vaginal agen­
esis, unless corrected operatively, precludes pregnancy by vagi­
nal intercourse. With MRKH syndrome, a functional vagina
can be created, but uterine agenesis proscribes childbearing. In
these women, however, ova can be retrieved for in vitro fer­
tilization (IVF) in a surrogate mother (F riedler, 20 1 6) . Uter­
ine transplantation is currently experimental but holds future
promise for these women Qohannesson, 20 1 6) .
Of other vaginal anomalies, congenital septa may form
longitudinally or transversely, and each can arise from a
fusion or resorption defect. Longitudinal septa divide the
vagina into right and left portions. hey may be complete
and extend the entire vaginal length. Partial septa usually
form high in the vagina but may develop at lower levels.
Septa are typically associated with other mullerian anomalies
(Haddad, 1 997) .
During labor, a complete longitudinal vaginal septum usu­
ally does not cause dystocia because the vaginal side through
which the fetus descends dilates satisfactorily. An incomplete
or partially obstructed longitudinal septum, however, may
interfere with descent. Occasionally, a woman with a distal
longitudinal septum presents in labor. During second-stage
labor, this septum usually becomes attenuated by pressure
from the fetal head. After ensuring adequate analgesia, the
inferior attachment of the septum is isolated, clamped, tran­
sected, and ligated. Following placenta delivery, the superior
attachment can be transected while carefully avoiding urethral
inj ury.
A transverse septum poses an obstruction of variable thick­
ness. It may develop at any depth within the vagina, but most
are in the lower third (Williams, 20 1 4) . These may or may not
be perforate, and thus obstruction or infertility is variably pres­
ent. In labor, perforate strictures may be mistaken for the upper
limit of the vaginal vault, and the septal opening is misidentiied
as an undilated cervical os (Kumar, 20 1 4) . If encountered during
labor, and ater the external os has dilated completely, the head
impinges on the septum and causes it to bulge downward. If the
septum does not yield, slight stretching pressure on its opening
usually leads to further dilatation, but occasionally cruciate inci­
sions are required to permit delivery (Blanton, 2003). If there
is a thick transverse septum, however, cesarean delivery may be
necessary.
• Cervical Abnormalities
Developmental abnormalities of the cervix include partial
or complete agenesis, duplication, and longitudinal septa.
Congenital Gen i tourinary Abnormalities
I. Hypoplasia/agenesis
A. Vaginal
C. Fundal
I I . Unicornuate
B. Cervical
D. Tubal
E. Combined
A. Communicating
B. No ncomm u nicating
C. No cavity
D. No horn
IV. Bicornuate
III. Didelphys
A. Complete
A. Complete
VII. DES related
VI. Arcuate
V. Septate
B. Partial
B. Partial
FIGURE 3-5 Clas s ifi catio n of mOllerian anomalies. DES
=
d i et hyl sti l bestrol. (Modified with permission from American Fertility Soc iety:
The American Fertility Society classifications of adnexal adhesions, distal tubal occ l us ion, tu ba l occ l u sion secon da ry to tubal l igation , tubal
pregnancies, M Ol i e ri an anomalies and intra uter i n e adhesions, Ferril Steril 1 988 Jun;49(6):944-55.l
Uncorrected complete agenesis is incompatible with preg­
nancy, and in vitro ferrilization with gestational surrogacy is
an option. Surgical correction by uterovaginal anastomosis has
resulted in successful pregnancy (Kriplani, 20 1 2). Significant
complications accompany this correcrive surgery, and rhe need
for clear preoperative anatomy delineation has been emphasized
by Rock (2010) and Roberrs (20 1 1 ) and their colleagues. For
this reason, they recommend hysterecromy for complete cervi�
cal agenesis and reserve reconsrruction a ttem prs for ca refu lly
selected patients with cervical dysgenesis .
• Uterine Abnormalities
From a large variery, a few of the m ore co m mon congenital
urerine malformations are shown in Table 3-3. An accurate
population prevalence of these is diicult to assess because the
best diagnostiC techniq ues are invasive. That said, the preva­
lence found with imaging ranges from 0.4 to 1 0 percent, and
rates in women with recurrent miscarri age are signiican tly
higher (Byrne. 2000; Dreisler. 2014; Saravclos. 2008). In a
general population, the mOSt common inding is arcuare urerus,
followed in descending order by septate, bicornuate, didelphic,
and unicornuate classes (Chan, 20 1 1 b).
Mullerian anomalies may be discovered during pelvic exam�
ination, cesarean delivery, rubal sterilization, or i n fertility eval­
uation. Depending on clinical presenrarion, diagnostic tools
may include sonography, hysterosalpingogra phy, magnetic�
resonance imaging, laparoscopy, and hysteroscopy. Each has
limitations, and rhese may be used in combination ro com­
pletely deine anatomy. In women undergoing fertiliry evalu­
ation, hysterosalpingography (HSG) is com monly selected for
uterine cavity and tubal patency assess ment. It is co ntraindi �
cared during pregnancy. HSG poorly deines the external urer­
ine contour and can delineate only patent cavities. Regarding
patency, remember that some uniconuate rudimentary horns
lack a caviry. Also, ourlet Obstructions will preclude dye illing.
In most clinical senings, rwo-dimensional transvaginal sonog­
raphy (2-D VS) is initially performed. For this indication, the
pooled accuracy for VS is 90 to 92 percent (Pellerito. 1 992).
Saline infusion sonography (SIS) improves delineation of the
endome[fium and intenal merine morphology, bur only with
a patent endometrial cavity. It also is contraindicated in preg­
nancy. Three-dimensional (3-D) sonography is more accurate
than 2 D sonography because i t provides uterine images from
virtually any angle. Thus, coronal images can be constructed as
shown in Figure 3-6, and these are essential in evaluating borh
·
43
44
Maternal Anatomy and Physiology
FIGURE 3-6 Th ree-dime n sion a l transvaginal sonographic images. A. Bicornuate uterus with an 8-week gestation. The external fundal
contour (red doted ine) dips centrally below the intercornual li ne, and the endometrial cavities communicate. B. Septate uterus with a
S-week gestation. The external fundal contour is normal and convex 'elow dotted ine), and the long septum (asterisk) extends caudad in
the midl ine. C. Arcuate uterus with an 8-week gestation. The external fundal contour is normal and convex (red dotted line), but the fundal
endometrial cavity is slightly indented (arrow).
internal and exrernaJ uterine contours (Grimbizis, 2 0 1 6) . Both
and diminished cavity size and muscle mass of the hemiurerus are
2-D and 3-D sonography arc suirable for use in pregnancy.
postulated ro underlie these risks (Donderwinkel, 1992).
Several
studies
have
reported very
good
concordance
Rudimentary horns also increase the risk for an ectopic
between 3-D TVS and MR imaging of muUerian anomalies
pregnancy within rhe remnant, which may be disastrous. This
(Deutch, 2008; Graupera, 2 0 1 5). MR imaging is often pre­
risk includes noncommunicating cavitary rudiments, for which
ferred for complex anatomy, especially cases for which correc­
transperironeal sperm migration permirs ovum fertilization and
tive surgery is planned. MR imaging provides clear delineation
pregnancy (Nahum, 2004). In a report of 70 sllch pregnancies,
of both the internal and external uterine anatomy and has a
Rolen and associares ( 1 966) found that the rudimentary uter­
reported accuracy of up to 100 percent for mullerian anomaly
ine horn ruptured prior to 20 weeks in most. Nahum (2002)
evaluation (Bermejo, 20 I 0; Pellerito, 1 992). In addition, com­
reviewed the literature from 1900 to 1 999 and identiied 588
plex anomalies and commonly associatcd secondary diagnoses
rudimentary horn pregnancies. Half had uterine rupture, and
such as renal or skeletal anomalies can be concurrendy evalu­
80 percent did so before the third rrimesrer. Of the rotal 588,
ated. Precautions wirh MR imaging in pregnancy are discussed
the neonatal survival race was only 6 percent.
in Chapter 46 (p. 9 1 0) .
Imaging allows an earlier diagnOSiS of rudimentary horn
I n some women undergoing a n inferrility evaluation. hyster­
pregnancy so that it can be treated either medically with meth­
oscopy and laparoscopy may be selected co assess for mullerian
otrexare or surgically before rupture (Dove, 2017; Edelman,
anomalies; screen for endomctriosis, which is often coexistent;
2003; Khati, 2012; Worley, 2008). lthough not emphasized
and exclude other tubal or uterine cavity pathologies (Pus­
in Figure 3-5, the anachmem sire between rhe rudimentary
check, 2008; Saravelo" 2008). In pregnancy, these approaches
horn at times can be broad and vascular.
are rarely used co diagnose mullerian anomalies. and hysteros­
copy is contraindicated.
U nicornuate Uterus (Class
II)
Wirh this abnormality, the underdeveloped o r rudimentary
horn may be absent. If present, it may or may nor communi­
cate
If diagnosed in a nonpregnant woman, mOSt recommend
prophylactic excision of a horn thac has a cavity (Fedele, 2005;
with the domin�nr horn �nd may or may not contain an
Rackow, 2007). Data regarding subsequent pregnancy after
excision are scarce. In one series of eight women, all had a pre­
term cesarean delivery ( pados, 2014).
Uterine Didel phys (Class
I I I)
endomerrium-Iined cavity (see Fig. 3-5). General population
This mullerian anomaly arises from a complere lack of fusion
estimates cite an incidence of I in 4000 women (Reichman,
rhat results in twO enrirely separate hemiureri, cervices, and
2009). This anomaly may be detected during ferrility evalua­
usually (yo vaginas (see Fig. 3-5). It is common among mar­
tion by HSG. Bur as nored, noncommunicating or noncavi­
supials, for example, the American possum-Didelphys vir­
rary rudimentary horns may not ill with dye. If this anomaly
giniana. Most women have a double vagina or a longitudinal
is suspected. 3-D sonography increases diagnostic accuracy,
vaginal septum. Urerine didelphys may be isolated. Or, it
but again MR imaging may be preferred. Importantly, 40
may compose a triad with an Qbstructed hemiyagina and with
percent of afected women will have renal anomalies (Fedele,
ipsilateral renal Igenesis (OHVlRA), also known as Herlyn­
1 996).
Werner-Wunderlich syndrome (Tong, 2013).
This mullerian anomaly carries signiicant obstetrical risks,
These anomalies are suspected on pelvic examinarion by
including first- and second-trimester miscarriage. malpresentation,
identificarion of a longitudinal vaginal septum and two cervi­
fetal-growth restricrion. fetal demise. prematurely ruprured mem­
ces. During HSG for fertility evaluation, contrast shows twO
branes, and preterm delivery (Chan, 20 1 1 a; Hua, 201 1 ; Reich­
separate endocervical canals. These open into separare noncom­
man, 2009). Abnormal uterine blood Row, cervicl incompetence,
municating fusiform endometrial cavities char each ends wirh a
Cong e n i ta l G e n ito u ri na ry A b norm a l ities
solitary fallopian tube. In women without fertility issues, 2- or
3-D TVS is a logical initial imaging tool, and separate diver­
gent uterine horns with a large intervening fundal cleft are seen.
Endometrial cavities are uniformly separate. MR imaging may
be valuable in cases without classic indings.
Adverse obstetrical outcomes associated with uterine didel­
phys are similar but less frequent than those seen with unicornu­
ate uterus. Increased risks include miscarriage, preterm birth, and
malpresentation (Chan, 20 1 1 a; Grimbizis, 200 1 ; Hua, 20 1 1 ) .
Metroplasty for either uterine didelphys o r bicornuate
uterus involves resection of intervening myometrium and fun­
dal recombination (Alborzi, 20 1 5) . hese rarely performed
surgeries are chosen for highly selected patients with otherwise
unexplained miscarriages. Moreover, no evidence-based data
conirm the eicacy of such surgical repair.
B i corn u ate Uterus (Class IV)
his fusion anomaly results in two hemiuteri. As shown in
Figure 3-5, the central myometrium runs either partially or
completely to the cervix. A complete bicornuate uterus may
extend to the internal cervical os and have a single cervix (bicor­
nuate unicollis) or reach the external os (bicornuate bicollis) . As
with uterine didelphys, a coexistent longitudinal vaginal sep­
tum is not uncommon.
Radiological discrimination of a bicornuate uterus from a
septate uterus can be challenging. This distinction, however,
is important because septate uterus can be treated with hys­
teroscopic septal resection. HSG or 2-D TVS may initially
suggest an anomaly, but further distinction is provided by
3-D TVS or MR imaging (see Fig. 3-6) . With these, an inter­
cornual angle greater than 1 0 5 degrees typiies a bicornuate
uterus, whereas one less than 75 degrees indicates a septate
uterus. Fundal contour also assists, and a straight line drawn
between the imaged tubal ostia serves as the defining thresh­
old. Referent to this, an intrafundal downward cleft mea­
suring � 1 em or more is indicative of bicornuate uterus. A
septate uterus shows a cleft depth < 1 em, or it may have a
normal fundal contour.
Bicornuate uterus carries increased risks for adverse obstet­
rical outcomes that include miscarriage, preterm birth, and
malpresentation. As discussed in the prior section, rare sur­
gical correction by metroplasty is reserved for highly selected
patients.
Septate Uteru s (Class V)
With this anomaly, a resorption defect leads to a persistent
complete or partial longitudinal uterine septum (see Fig. 3-5).
Less often, a complete vaginocervicouterine septum is found
(Ludwin, 20 1 3) . Many septate uteri are identiied during eval­
uation of infertility or recurrent pregnancy loss. Although an
abnormality may be identiied with HSG or 2-D TVS, typi­
cally 3-D TVS or MR imaging is required to diferentiate this
from a bicornuate uterus (see Fig. 3-6) .
Septate anomalies are associated with diminished fertil­
ity and increased risks for adverse pregnancy outcomes that
include miscarriage, preterm delivery, and malpresentation
(Chan, 20 1 1 a; Ghi, 20 1 2) . Hysteroscopic septal resection has
been shown to improve pregnancy rates and outcomes (Mollo,
2009; Pabu:cu, 2004) . F rom their metaanalysis, Valle and
colleagues (20 l 3) reported a 63-percent pregnancy rate and
50-percent live birth rate following resection.
Arcuate Uteru s (Class VI)
his malformation is a mild deviation from the normally devel­
oped uterus. Although some studies report no increased adverse
associated outcomes, others have found excessive second­
trimester losses, preterm labor, and malpresentation (Chan,
2 0 1 1 a; Mucowski, 20 1 0; Woelfer, 200 1 ) .
Treatment with Cerclage
Some women with uterine anomalies and repetitive pregnancy
losses may beneit from transvaginal or transabdominal cervi­
cal cerclage (Golan, 1 992; Groom, 2004) . Others with partial
cervical atresia or hypoplasia may also benefit (Hampton, 1 990;
Ludmir, 1 99 1 ) . Candidacy for cerclage is determined by the
same criteria used for women without such defects, which is
discussed in Chapter 1 8 (p. 3 54) .
• Diethylstilbestrol Reproductive Tract
Abnormalities (Class VII)
During the 1 960s, a synthetic nonsteroidal estrogen-dieth­
ylstilbestrol (DES)-was used to treat pregnant women for
threatened abortion, preterm labor, preeclampsia, and diabe­
tes. he treatment was remarkably inefective. Later, it was
also discovered that women exposed as fetuses had increased
risks of developing several specific reproductive-tract abnor­
malities. hese included vaginal clear cell adenocarcinoma,
cervical intraepithelial neoplasia, small-cell cervical carci­
noma, and vaginal adenosis. Afected women had identii­
able structural variations in the cervix and vagina that include
transverse septa, circumferential ridges, and cervical collars.
Uteri potentially had smaller cavities, shortened upper uter­
ine segments, or T-shaped and other irregular cavities (see
Fig. 3-5) (Kaufman, 1 984) .
These women sufer impaired conception rates and higher
rates of miscarriage, ectopic pregnancy, and preterm delivery,
especially in those with structural abnormalities (Kaufman,
2000; Palmer, 200 1 ) . Now, more than 50 years after DES use
was proscribed, most afected women are past childbearing age,
but higher rates of earlier menopause, cervical intraepithelial
neoplasia, and breast cancer are reported in exposed women
(Hatch, 2006; Hoover, 2 0 1 1 ; Troisi, 20 1 6) .
• Fallopian Tube Abnormalities
he fallopian tubes develop from the unpaired distal ends
of the mlillerian ducts. Congenital anomalies include acces­
sory ostia, complete or segmental tubal agenesis, and several
embryonic cystic remnants. The most common is a small,
benign cyst attached by a pedicle to the distal end of the fal­
lopian tube-the hydatid of Morgagni. In other cases, benign
paratubal cysts may be of mesonephric or mesothelial origin.
Last, in utero exposure to DES is associated with various
tubal abnormalities. Of these, short, tortuous tubes or ones
with shriveled fi m bria and small ostia are linked to infertility
(DeCherney, 1 98 1 ) .
45
46
Mate r n a l A n ato my a n d Phys i ology
Conscious sedation, spinal analgesia, or general anesthesia may
be necessary. Following repositioning, the catheter is left in
place until bladder tone returns. Insertion of a soft pessary for
The pregnant uterus may infrequently show exaggerated flex­
a few weeks usually prevents recurrent incarceration.
ion. M ild or moderate lexion is typically inconsequential, but
Lettieri and colleagues ( 1 994) described seven cases of uter­
congenital or acquired extremes may lead to pregnancy com­
ine incarceration not amenable to these simple procedures. In
plications.
two women, laparoscopy was used at 1 4 weeks' gestation to
Antlexion describes forward angling of the uterine fundus
reposition the uterus using the round ligaments for traction.
in the sagittal plane relative to the cervix. Exaggerated degrees
Alternatively, in case series, advancing a colonoscope or colono­
usually pose no problem in early pregnancy. Later, however,
scopic insulation was used to dislodge an incarcerated uterus
particularly when the abdominal wall is lax such as with dias­
(Dierickx, 20 1 1 ; Newell, 20 1 4; Seubert, 1 999) .
tasis recti or ventral hernia, the uterus may fall forward. In
Rarely, sacculation may form as extensive lower uterine
extreme cases, the fundus lies below the lower margin of the
segment dilatation due to persistent entrapment of the preg­
symphysis. Sometimes, this abnormal uterine position prevents
nant uterus in the pelvis (Fig. 3 -7) . In these extreme cases,
proper transmission of labor contractions, but this is usually
sonography and MR imaging are typically required to deine
overcome by repositioning and application of an abdominal
anatomy (Gottschalk, 2008; Lee, 2008). Cesarean delivery is
binder.
necessary when sacculation is marked, and Spearing ( 1 978)
Retrolexion describes posterior uterine fundal angling in the
stressed the importance of clariying the distorted anatomy.
sagittal plane. A growing retrolexed uterus will occasionally
An elongated vagina passing above the level of a fetal head
become incarcerated in the hollow of the sacrum. Symptoms
that is deeply placed into the pelvis suggests a sacculation
include abdominal discomfort, pelvic pressure, and voiding
or an abdominal pregnancy. The Foley catheter is frequently
dysfunction or retention. D uring bimanual pelvic examina­
palpated above the level of the umbilicus! Spearing ( 1 978)
tion, the cervix wil l be anterior and behind the symphysis
recommended extending the abdominal incision above the
pubis, whereas the uterus is appreciated as a mass wedged in
umbilicus and delivering the entire uterus from the abdo­
the pelvis. Sonography or MR imaging can aid the clinical
men before hysterotomy. This will restore correct anatomi­
diagnosis (Gardner, 20 1 3 ; Grossenburg, 20 1 1 ; van Beekhui­
cal relationships and prevent inadvertent incisions into and
zen, 2003) .
through the vagina and bladder. Unfortunately, this may not
With continued uterine growth, the incarcerated uterus can
always be possible (Singh, 2007) . As a inal caveat, a true
spontaneously resolve over 1 to 2 weeks. An indwelling uri­
uterine diverticulum has been mistaken for uterine saccula­
nary catheter or intermittent self-catheterization may be needed
tion (Rajiah, 2009) .
in the interim to empty the bladder. Persistent cases require
he uterus commonly rotates to the maternal right dur­
manual repositioning. For this, after bladder catheterization,
ing pregnancy. Rarely, uterine rotation exceeds 1 80 degrees to
the uterus can usually be pushed out of the pelvis when the
cause torsion. Most cases of torsion result from uterine leiomy­
woman is placed in a knee-chest position. Often, this is best
omas, miillerian anomalies, fetal malpresentation, pelvic adheaccomplished by digital pressure applied through the rectum.
sions, or laxity of the abdominal wall
or uterine ligaments. Jensen ( 1 992)
reviewed 2 1 2 cases and reported that
associated symptoms may include
obstructed labor, intestinal or urinary
complaints, abdominal pain, uterine
--- Anterior wal l
sacculation
hypertonus, vaginal bleeding, and
hypotension.
Most cases of uterine torsion are
found at the time of cesarean deliv­
ery. In some women, torsion can be
Placenta --.conirmed preoperatively with MR
imaging, which shows a twisted vagina
that appears X-shaped rather than its
normal H -shape (Nicholson, 1 995).
As with uterine incarceration, during
Posterior ----����.-�
cesarean delivery, a severely displaced
uterin e wal l
uterus should be repositioned ana­
tomically before hysterotomy. In some
cases, an inability to reposition or a
failure to recognize the torsion may
lead to a posterior hysterotomy inci­
sion
(Albayrak, 2 0 1 1 ; Picone, 2006;
FIGURE 3-7 Anterior saccu lation of a preg n a nt uterus. Note the m a rkedly atten uated a nte­
Rood, 20 1 4) .
rior uteri ne wa l l a nd atypica l location of the true uterine fu n d u s .
UTERINE FLEXION
Congenital Genitourinary Abnorma l ities
.swara )R, Kielb S, Koyle MA. et al: The recommendations of the 20 1 5 Ameri­
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49
C H A PT E R 4
M a te r n a l P hys i o l ogy
REPRODUCTIVE TRACT . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
BREASTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
SKIN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
METABOLIC CHANGES . . . . . . . . . . . . . . . . . . . . . . . . . . . 54
H EMATOLOGICAL CHANGES . . . . . . . . . . . . . . . . . . . . . . 57
to her prepregnancy state after delivery and lactation. Most
pregnancy-related changes are prompted by stimuli provided
by the fetus and placenta. Virtually every organ system under­
goes alterations, and these can appreciably modiy criteria for
disease diagnosis and treatment. hus, an understanding of
pregnancy adaptations is essential to avoid misinterpretation.
Moreover, some physiological changes can unmask or worsen
preexisting disease.
CARDIOVASCU LAR SYSTEM . . . . . . . . . . . . . . . . . . . . . . . 60
RESPI RATORY TRACT. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64
URINARY SYSTEM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65
GASTROI NTESTINAL TRACT . . . . . . . . . . . . . . . . . . . . . . . 68
ENDOCRINE SYSTEM . . . . . . . . . . . . . . . . . . .
.
. . . . . .
.
. . 68
MUSCU LOSKELETAL SYSTEM . . . . . . . . . . . . . . . . . . . . . . 72
CENTRAL N ERVOUS SYSTEM . . . . . . . . . . . . . . . . . . . . . . 72
The matenal organism reacts to a greater or lesser extent
under the inluence ofpregnancy, but naturaly the most
characteristic changes are observed in the generative tract,
and especialy the uterus, which undergoes a very marked
increase in size.
-J. Whitridge Williams ( 1 903)
In the irst edition of this textbook, Williams devoted only 1 0
pages to the physiology of pregnancy, and half were focused
on uterine growth. Many gestational changes begin soon after
fertilization and continue throughout pregnancy. Equally
astounding is that the woman is returned almost completely
REPRODUCTIVE TRACT
• Uterus
In the nonpregnant woman, the uterus weighs approximately
70 g and is almost solid, except for a cavity of 1 0 mL or less.
During pregnancy, the uterus is transformed into a thin-walled
muscular organ of suicient capacity to accommodate the fetus,
placenta, and amnionic luid. he total volume of the contents
at term averages 5 L but may be 20 L or more! hus, by the
end of pregnancy, the uterus has achieved a capacity that is
500 to 1 000 times greater than the nonpregnant state. The cor­
responding increase in uterine weight is such that, by term, the
organ weighs nearly 1 1 00 g.
D uring pregnancy, uterine enlargement involves stretching
and marked hypertrophy of muscle cells, whereas the produc­
tion of new myocytes is limited. Fibrous tissue also accumu­
lates, particularly in the external muscle layer, together with
a considerable rise in elastic tissue content. The walls of the
corpus considerably thicken and strengthen during the first few
months of pregnancy but then gradually thin. By term, the
myometrium is only 1 to 2 cm thick, and the fetus usually can
be palpated through the soft, readily indentable uterine walls.
Uterine hypertrophy early in pregnancy probably is stimu­
lated by the action of estrogen and perhaps progesterone. Thus,
similar uterine changes can be observed with ectopic pregnancy.
But after approximately 1 2 weeks' gestation, uterine growth is
50
Mate r n a l Anatomy and P hys i o logy
related predominantly to pressure exerted by the expanding
products of conception.
Within the uterus, enlargement is most marked in the fun­
dus. The extent of uterine hypertrophy is also influenced by the
position of the placenta. Namely, the myometrium surround­
ing the placental site grows more rapidly than does the rest.
Myocyte Arra ng e ment
The uterine musculature during pregnancy is arranged in three
strata. The irst is an outer hoodlike layer, which arches over the
fundus and extends into the various ligaments. The middle layer
is a dense network of muscle fibers perforated in all directions
by blood vessels. Last is an internal layer, with sphincter-like
ibers around the fallopian tube orifices and internal cervical os.
Most of the uterine wall is formed by the middle layer. Here,
each myocyte has a double curve so that the interlacing of any
two cells forms a fi g ure eight. This arrangement is crucial and
permits myocytes to contract after delivery and constrict pen­
etrating blood vessels to halt bleeding.
Uteri ne S h a pe a nd Position
For the first few weeks, the uterus maintains its original piri­
form or pear shape. But, as pregnancy advances, the corpus and
fundus become globular and almost spherical by 1 2 weeks' ges­
tation. Subsequently, the organ grows more rapidly in length
than in width and becomes ovoid. By the end of 1 2 weeks, the
enlarged uterus extends out of the pelvis. With this, it contacts
the anterior abdominal wall, displaces the intestines laterally
and superiorly, and ultimately reaches almost to the liver. With
uterine ascent, it usually rotates to the right, and this dextro­
rotation likely is caused by the rectosigmoid on the left side of
the pelvis. As the uterus rises, tension is exerted on the broad
and round ligaments.
With the pregnant woman standing, the longitudinal axis of
the uterus corresponds to an extension of the pelvic inlet axis.
The abdominal wall supports the uterus and maintains this axis,
unless the wall is lax. When the pregnant woman lies supine,
the uterus falls back to rest on the vertebral column and the
adjacent great vessels.
• Uterine Contractility
Beginning in early pregnancy, the uterus contracts irregularly,
and these may be perceived as mild cramps. During the sec­
ond trimester, these contractions can be detected by bimanual
examination. In 1 872, J . Braxton Hicks first brought atten­
tion to these contractions, which now bear his name. hese
appear unpredictably and sporadically and are usually non­
rhythmic. Their intensity varies between 5 and 25 mm Hg
(Alvarez, 1 950) . Until near term, these Braxton Hicks contrac­
tions are infrequent, but their number rises during the last
week or two. At this time, the uterus may contract as often
as every 1 0 to 20 minutes and with some degree of rhyth­
micity. Correspondingly, uterine electrical activity is low and
uncoordinated early in gestation, but becomes progressively
more intense and synchronized by term (Garield, 200 5 ;
Rabotti, 20 1 5) . This synchrony develops twice a s fast i n mul­
tiparas compared with nulliparas (Govindan, 20 1 5) . Late in
pregnancy, these contractions may cause some discomfort and
account for so-called false labor.
• Uteroplacental Blood Flow
The delivery of most substances essential for fetal and placental
growth, metabolism, and waste removal requires the placental
intervillous space to be adequately perfused (Chap. 5, p. 94) .
Placental perfusion depends on total uterine blood low, but
simultaneous measurement of uterine, ovarian, and collateral
vessels is not yet possible, even using magnetic resonance (MR)
angiography (Pates, 20 1 0) . Using ultrasound to study the uter­
ine arteries, uteroplacental blood low has been measured to
increase progressively during pregnancy-from approximately
450 mUmin in the mid trimester to nearly 500 to 750 mU
min at 36 weeks (Flo, 20 1 4; Wilson, 2007) . hese measures are
similar to uterine artery blood flow estimates ascertained indi­
rectly using clearance rates of androstenedione and xenon- 1 33
(Edman, 1 98 1 ; Kauppila, 1 980) . These values also mirror older
ones-500 to 750 mUmin-obtained with invasive methods
(Assali, 1 953; Browne, 1 953; Metcalfe, 1 955) . Logically, such
massively increased uteroplacental blood flow requires adapta­
tion of the uterine veins as well. The resultant increased venous
caliber and distensibility can result in uterine vein varices that
in rare instances may rupture (Lim, 20 1 4) .
As noted irst from animal studies, uterine contractions,
either spontaneous or induced, lower uterine blood fl o w pro­
portionally to contraction intensity (Assali, 1 968) . A tetanic
contraction yields a precipitous fall in uterine blood fl o w. In
humans, three-dimensional power Doppler angiography has
also demonstrated reduced uterine blood low during contrac­
tions Gones, 2009) . Using a similar technique, resistance to
blood low in both maternal and fetal vessels was found to be
greater during the second stage of labor compared with the first
(Baron, 20 1 5) . Given that baseline uterine blood low is dimin­
ished in pregnancies complicated by fetal-growth restriction,
these fetuses may tolerate spontaneous labor less efectively
(Ferrazzi, 20 1 1 ; Simeone, 20 1 7) .
Utero p lacenta l Blood F low Reg u l ation
The vessels that supply the uterine corpus widen and elongate
yet preserve their contractile function (Mandala, 20 1 2) . In
contrast, the spiral arteries, which directly supply the placenta,
vasodilate but completely lose contractility. This presumably
results from endovascular trophoblast invasion that destroys
the intramural muscular elements (Chap. 5, p. 9 1 ) . It is this
vasodilation that allows maternal-placental blood low to pro­
gressively rise during gestation. Given that blood fl o w increases
proportionally to the fourth power of the radius of the vessel,
small increases in vessel diameter result in tremendous aug­
mentation of uterine artery blood low. For example, in one
study, the uterine artery diameter grew from only 3.3 mm to
3.7 mm between 22 and 29 weeks' gestation, but mean velocity
increased 50 percent, from 29 to 43 cm/sec (Flo, 20 1 0) .
The downstream fall i n vascular resistance is another key
factor that accelerates low velocity and shear stress in upstream
vessels. In turn, shear stress leads to circumferential vessel
growth. Nitric oxide-a potent vasodilator-appears to play
Maternal Physiology
a central role in regulating this process and is discussed later
(p. 63). Indeed, endothelial shear stress and several hormones
and growth facrors all augment endorhelial nitric oxide synthase
(eNOS) and nitric oxide producrion (Crummer, 2009; Lim,
20 1 5; Mandala, 2 0 1 2 ; Pang, 20 1 5). Facrors include estrogen,
progesterone, activin, placental growth facror (PIG F), and vas­
cular endorhelial growrh factor (VEGF), which is a promoter of
angiogenesis. As an impo((am aside, VEGF and PIGF signaling
is attenuated in response to excess placenral secretion of their
soluble recepror-soluble FMS-like yrosille kinase I (sFlt- I). An
elevated maternal sFlt-l level inactivares and lowers circular­
ing PIGF and VEGF concentrations and is importanr in pre­
eclampsia parhogenesis (Chap. 40, p. 7 1 6).
Normal pregnancy is also characterized by vascular refrac­
mriness CO the pressor efects of infused angiotensin II, and
rhis raises ureropiacenral blood Aow (Rosenfeld, 1 98 1 , 20 1 2).
Other factors that augmenr urcroplacenral blood Aow include
relaxin and certain adipocyrokines (Vodsrrcil, 201 2). Chemeri1
is an adipocycokine secreted by several rissues, including the
placenra (Garces, 2 0 1 3 ; Kasher-Meron, 2 0 1 4). Irs concentra­
tion rises as gestadon advances and serves ro i ncrease human
umbilical eNOS activity, which mediates greater blood Aow
(Wang, 2 0 1 5). Anorher adipocyrokine-viotil-raises VEGF
secretion and VEGF recepror 2 expression in human epithelial
cells derived from the placemal amnion (Astern, 20 1 3). Orher
adipocyrokines include lepfin, resistin, and 1diponectin, which
all enhance human umbitical vein endorhelial cell proliferation
(Pole', 2014).
Last, cenain micro RNA species mediate vascular remodel­
ing and uterine blood low early in placentation (Sama, 2 0 1 5).
In particular, members of the miR-1 7-92 clusrer and miR-34
are i mportant in spiral artery remodeling and invasion. Abnor­
malities of micro-RNA function have been reported in pre­
eclampsia, fetal-growth rescriction, and gestational diaberes.
• Cervix
As early as 1 momh after conception, the cervix begins to soften
and gain bluish mnes. These result from increased vascularity
and edema of the entire cervix, from changes in the collagen
necwork, and from hypertrophy and hyperplasia of the cervical
glands (Peralra, 20 1 5; Srraach, 2005). Alrhough rhe cervix con­
tains a small amollnt of smooth muscle, its major componenr
is connective (issue. Rearrangemem of rhis collagen-rich tis­
sue aids rhe cervix in retention of the pregnancy until term, i n
dilatation to aid delivery, and i n posrpartum repair and recon­
stitution ro permir a subsequenr successful pregnancy (Myers,
20 1 5). As derailed in Chapter 2 1 (p. 409), cervical ripening
involves connective tissue remodeling (har lowers collagen and
proreoglycan concentrations and raises warer comenr compared
wirh rhe nonpregnanr cervix.
Cervical glands undergo marked proliferation, and by the
end of pregnancy, they occupy up to one half of the entire cer­
vical mass. This normal pregnancy-induced change promprs an
extension, or eversion, of (he proliferating columnar endocervi­
cal glands onto the ecrocervical portio (rig. 4- 1 ). This tissue
appears red and velvety and bleeds even with minor trauma,
such as with Pap tesring.
FIGURE 4-1 Cervical eversion of pregnancy a s viewed through a
colposcope. The eversion represents columnar epithelium on the
portio of the cervix. (Used with permission from Dr. Claudia Werner.)
The endocervical mucosal cells produce copious amounts
of tenacious mucus thar obstruct the cervical canal soon after
conception (Bastholm, 20 17). This mucus is rich in immuno­
globulins and cytokines and may acr as an immunological bar­
rier to prorec( the uterine conrents against infection (Hansen,
2014; Wang, 2014). Ar labor onser, if not before, this mucus
plug is expelled, resulting in a bloody show. Moreover, the cervi­
cal mucus consistency changes during pregnancy. Speciically,
in most pregnant women, as a result of progesterone, when
cervical mucus is spread and dried on a glass slide, it shows poor
crysrall ization, termed beading. In some gravidas, as a resulr
of amnionic Auid leakage. an arborization of ice-like crystals,
called ening, is seen microscopically.
HistOlogically, basal cells near rhe squamocolumnar junction
can be prominenr in size, shape, and staining quality in preg­
nancy. 111ese changes are considered ro be estrogen induced. I n
addition, pregnancy i s associated with bO[h endoccrvical gland
hyperplasia and hypersecretory appearance-the Arias-Stela
raction which can make diferenriating these from truly
atypical glandular cells during Pap test evaluarion particularly
diiculr (Rosai, 20 1 5).
-
• Ovaries
Ovularion ceases during pregnancy, and maturation of new
follicles is suspended. The single corpus luteum found in
graVidas functions maximally during the irst 6 to 7 weeks of
pregnancy--4 ro 5 weeks postovulation. Thereafter, ir contrib­
utes relarively linie to progesrcrone production. Surgical removal
of the corpus luteum before 7 weeks prompts a rapid fall in
matenal serum progesrerone levels and spontaneous abortion
(Csapo, 1 973). Afrer this time, however, corpus lureum excision
ordinarily does nO[ cause abortion.
An extrauterine decidual reaction on and jusr beneath
the ovarian surface is common in pregnancy and is usually
observed ar cesarean delivery. 1l1ese slighdy elevated clear or
red patches bleed easily and may, on irst glance, resemble
freshly torn adhesions. Similar decidual reactions arc seen
51
52
Maternal Anatomy and Physiology
on the uterine serosa and other pelvic, or even extrapelvic,
abdominal organs (Bloom. 20 1 0) . These areas arise from
subcoelomic mesenchyme or eniomcrcioric lesions that have
been stimulated by progesterone. They histologically appear
similar
to
progestin-stimulated
intrauterine endometrial
stroma (Kim. 20 1 5) .
The enormous caliber o f the ovarian veins viewed a t cesarean
delivery is starding. Hodgkinson ( 1 953) found that the diam­
etcr of the ovarian vascular pedicle increased during pregnancy
from 0.9 em to approximately 2.6 em at term. Again, recall
that Aow in a tubular structure increases exponentially as the
diameter enlarges.
• Fallopian Tubes
The fallopian rube musculature, rhat is, the myosalpinx, under­
goes little hypertrophy during pregnancy. The epithelium of
the
mdosnpinx somwhat Ranens.
Decidual cells may develop
in rhe stroma of the endosalpinx, but a continuous decidual
membrane is not formed.
Rarely, a fallopian tube may twisr during uterine enlarge�
mem (Macedo, 2017). This torsion is more common with
comorbid pararubal or ovarian cysts (Lee, 2 0 1 5 ) .
• Vagina and Perineum
During pregnancy, greater vascularity and hyperemia develop
Relaxin
in the skin and muscles of the perineum and vulva, and the
This protein hormone is secreted by the corpus lureum, the
underlying abundant connective tissue softens. This augmented
decidua. and the placenta in a pattern similar to that of human
vascularity prominently afects the vagina and cervix and results
chorionic gonadotropin (hCG) (Chap. 5. p. 1 02). Relaxin
in the violet color characreristic of Chadwick sign.
here because its secretion by the corpus lureum appears to aid
cervical secretions during pregnancy forms a somewhat thick,
many maternal physiological adaptations, such as remodeling
white discharge. The pH is acidic, varying from 3 . 5 to 6. This
of reproductive-tract connective tissue to accommodate labor
pH results from increased production of lactic acid by lactoba­
(Conrad. 2 0 1 3 ; Vrachnis. 2 0 1 5). Relaxin also appears impor­
cillus acidophi/us during metabolism of glycogen energy stores
is also expressed in brain, hean, and kidney. Ie is mentioned
Within the vagina, the considerably elevated volume of
tam in initiating augmented renal hemodynamics, lowering
in the vaginal epithelium. Pregnancy is associated with an ele­
serum osmolality, and increasing arterial compliance, which are
vated risk of vulvovaginal candidiasis. particularly during the
all associated with normal pregnancy (Conrad. 20 1 4a). Despite
second and third trimesters. Higher infection rates may stem
its name, serum relaxin levels do nOt contribute to greater
from immunological and hormonal changes and from greater
peripheral joint laxity or pelvic girdle pain during pregnancy
vaginl glycogen stores (Aguin. 2 0 1 5 ) .
(Aldabe. 2 0 1 2 ; Marnach. 2003; V0l1estad. 2012).
The vaginal walls undergo striking changes i n preparation
for the distention that accompanies labor and delivery. These
Theca-Lutein Cysts
alterations include considerable epithelial thickening, connec­
These benign ovarian lesions reAect exaggerated physiologi­
cal follicle stimulation, which is termed hyperreactio luteinalis.
tive tissue loosening, and smooth muscle cell hypertrophy.
These usually bilateral cystic ovaries are moderately to massively
Pelvic Organ Prolapse
enlarged. The reaction is usually linked to markedly elevated
Pelvic Organ Prolapse Quantiication (POP-Q) and three­
serum heG levels. Logically, theca-Iurein CYStS are found fre­
dimensional sonography studies show that vaginal suppOrt
quenrlywith gestational trophoblastic disease (Fig. 20-3. p. 3 9 1 ) .
changes across pregnancy. In particular, vaginal lengthening,
They also can develop with the placentomegaly that can accom­
posterior vaginal wall and hiatal relaxation, increased levaror
pany diabetes, anti-D alloimmunization, and multifetal gesta­
hiaral area, and greater irst-trimester vaginal elastase activity are
tion (Malinowski, 2 0 1 5). Hyperreactio luteinalis is associated
all associated with uncomplicated spontaneous vaginal delivery
with preeclampsia and hyperthyroidism, which may contribure
(Oliphant. 2014). The larger hiatal area persists in women who
to elevated risks for fetal-growth restriction and preterm birth
deliver vaginally compared with women delivering by prelabor
(Cavorerro. 2 0 1 4 ; Lynn. 2 0 1 3; Mlinowski. 201 5). hese cystS
or early-labor cesarean delivery. However. all women show
also are encountered in women with otherwise uncomplicated
greater hiatal distensibility after delivery, which is potentially
pregnancies. In these cases, an exaggerated response
of the ova­
ries to normal levels of circulating heG is suspected (Sarmento
Gon,alves. 2 0 1 5 ) .
Although
usually
a facror in later pelvic floor dysfunction (van Veelen, 20 1 5) .
In women with apical vaginal prolapse. the cervix, and occa­
sionally a portion of the uterine body, can protrude variably
asymptomatic,
hemorrhage
into
the
from the vulva during early pregnancy. With further growth.
CYStS can cause acme abdominal pain (Amoah. 20 1 1 ). Mater­
the uterus usually rises above the pelvis and can draw the cervix
nal virilization may be seen in up to 30 percent of women,
up with it. If the uterus persists in its prolapsed position, symp­
however, virilization of the fetus has only rarely been reported
toms of incarceration may develop at 1 0 to 1 4 weeks' gestation
(Malinowski. 2 0 1 5). Maternal indings that include temporal
(Chap. 3, p. 46). s a preventive measure. [he urerus can be
balding, hirsutism, and clitoromegaly are associated with mas­
replaced early in pregnancy and held in position with a suitable
sively elevated levels of androstenedione and testosterone. The
pessary.
diagnosis typically is based on sonographic findings of bilateral
Attenuation of anterior vaginal wall suppOrt can lead to pro­
enlarged ovaries containing multiple cysts in the appropriate
lapse of the bladder, that is, a cystocele. Urinary stasis with a
clinical settings. The condition is self-limited and resolves fol­
cystocele predisposes to infection. Pregnancy may also worsen
lowing delivery. Its management is reviewed by Malinowski
coexistent stress urinary incontinmce (SUi), likely because ure­
(20 1 5) and discussed further in Chapter 63 (p. 1 1 99).
rhral closing pressures do nor risc suiciently to compensate
Matern a l Phys i o l ogy
for altered bladder neck support. Urinary incontinence afects
nearly 20 percent of women during the first trimester and
nearly 40 percent during the third trimester. Most cases stem
from SUI rather than urgency urinary incontinence (Abdullah,
20 1 6a; Franco, 20 1 4; Iosif, 1 980) . In primigravidas, maternal
age greater than 30 years, obesity, smoking, constipation, and
gestational diabetes mellitus are all risk factors associated with
SUI development during pregnancy (Sangsawang, 20 1 4) .
Attenuation o f posterior vaginal wall support can result i n a
rectocele. A large defect may fill with feces that occasionally can
be evacuated only digitally. During labor, a cystocele or recto­
cele can block fetal descent unless they are emptied and pushed
out of the way. Rarely, an enterocele of considerable size may
bulge into the vagina. If the mass interferes with delivery, the
hernia sac and its abdominal contents are gently reduced to
permit fetal descent.
BREASTS
In early pregnancy, women often experience breast tenderness
and paresthesias. Mter the second month, the breasts grow in
size, and delicate veins are visible just beneath the skin. he
nipples become considerably larger, more deeply pigmented,
and more erectile. Mter the fi r st few months, a thick, yellowish
luid-colosrum-can often be expressed from the nipples by
gentle massage. D uring the same months, the areolae become
broader and more deeply pigmented. Scattered through each
areola are several small elevations, the glands of Montgomey,
which are hypertrophic sebaceous glands. If breasts gain exten­
sive size, skin striae similar to those observed in the abdo­
men may develop. Rarely, breasts can become pathologically
enlarged-referred to as gigantomastia-which may require
postpartum surgical reduction (Fig. 4-2) (Eler Dos Reis, 20 1 4;
Rezai, 20 1 5) .
For most normal pregnancies, prepregnancy breast size and
ultimate volume of breast milk do not correlate, as multiple
factors infl u ence milk production (Hartmann, 2007) . These
factors and gestation breast changes are further discussed in
Chapter 36 (p. 656) .
SKI N
Skin changes are common, and Fernandes and Amaral (20 1 5)
described dermatological changes in more than 900 pregnant
women. They found at least one physiological cutaneous change
in 89 percent of the women examined. Dermatologic patholo­
gies during pregnancy are found in Chapter 62.
• Abdominal Wall
Beginning after midpregnancy, reddish, slightly depressed
streaks commonly develop in the abdominal skin and some­
times in the skin over the breasts and thighs. These are called
striae gravidarum or stretch marks. In multiparas, glistening,
silvery lines that represent the cicatrices of previous striae fre­
quently coexist. In one study of 800 primiparas, 70 percent
developed striae gravidarum on their abdomen; 33 percent on
their breasts; and 4 1 percent on their hips and thighs (Picard,
20 1 5) . The strongest associated risk factors included younger
maternal age, family history, and prepregnancy weight and
weight gain during pregnancy. The etiology of striae gravi­
darum is unknown, and there are no preventive steps or defini­
tive treatments (Korgavkar, 20 1 5) .
Occasionally, the muscles o f the abdominal walls do not
withstand the tension of the expanding pregnancy. As a result,
rectus muscles separate in the midline, creating diastasis recti of
varying extent. If severe, a considerable portion of the anterior
uterine wall is covered by only a layer of skin, attenuated fascia,
and peritoneum to form a ventral hernia.
• Hyperpigmentation
This develops in up to 90 percent of women and is usually more
accentuated in those with darker complexion (Ikino, 20 1 5) . Of
speciic sites, the pigmented skin line in the midline of the ante­
rior abdominal wall-the linea alba-takes on dark brown­
black pigmentation to form the linea nigra. Occasionally,
irregular brownish patches of varying size appear on the face
and neck, giving rise to chloasma or melasma gravidarum-the
mask of pregnancy. Pigmentation of the areolae and genital
skin may also be accentuated. Mter delivery, these pigmentary
changes usually disappear or at least regress considerably. Oral
contraceptives may cause similar alterations (Handel, 20 1 4) .
he etiology o f these pigmentary changes is incompletely
understood, however, hormonal and genetic factors play a
role. For example, levels of melanocyte-stimulating hormone,
a polypeptide similar to corticotropin, are elevated remarkably
throughout pregnancy, and estrogen and progesterone also are
reported to have melanocyte-stimulating efects .
• Vascular Changes
FIGURE 4-2 Giga ntomastia in a woma n near term. (U sed with
perm ission from Dr. Patricia Sa ntiago-Munoz.)
Angiomas, called vascular spiders, are particularly common
on the face, neck, upper chest, and arms. These are minute,
red skin papules with radicles branching out from a central
lesion. he condition is often designated as nevus, angioma,
53
54
Matern a l A n atomy a n d P hysio l ogy
TABLE 4-1 . Add itional Energy Dema n d s D u r i n g Normal Preg nancya
Rates of Tissue Deposition
1 st Trimester 2nd Trimester 3rd Trimester
g/d
g/d
g/d
Wei g h t g a i n
P rote i n d e position
Fat deposition
17
o
5 .2
60
1 .3
1 8.9
Total Deposition
g/280 d
54
5.1
1 6.9
1 2,000
597
3 74 1
Energy Cost o f Pregnancy Esti mated from Basa l Metabolic Rate a n d Energy Deposition
1 st Trimester
kJ/d
P rot e i n deposition
Fat deposition
Effi c i ency of energy util ization b
Basa l meta bol i c rate
Total energy cost of pregnancy
0
202
20
1 99
42 1
2nd Trimester
kJ/d
30
732
76
397
1 235
3 rd Trimester
kJ/d
Total Energy Cost
MJ
Kcal
1 4. 1
1 44.8
1 5 .9
1 47.8
322.6
121
654
77
993
1 845
3 3 70
34,600
3800
35,1 30
77, 1 00
aAssumes a n average g estat i o n a l wei g h t g a i n of 1 2 kg .
b Efficiency of food energy uti l izat i o n for p rote i n a n d fat deposition est i mated as 0.90.
Ada pted from the World Health O rg a n izati o n , 2004.
or telangiectasis. Palmar eythema is encountered during preg­
nancy. Both conditions lack clinical significance and disappear
in most gravidas shortly after pregnancy. hey are likely the
consequence ofhyperestrogenemia. In addition to these discrete
lesions, increased cutaneous blood flow in pregnancy serves to
dissipate excess heat generated by the augmented metabolism.
• Hair Changes
hroughout life, the human hair follicle undergoes a pattern
of cyclic activity that includes periods of hair growth (anagen
phase) , apoptosis-driven involution (catagen phase) , and a rest­
ing period (telogen phase) . Based on a study of 1 1 6 healthy
pregnant women, the anagen phase lengthens during preg­
nancy and the telogen rate increases postpartum (Gizlenti,
20 1 4) . Neither is exaggerated in most gravidas, but excessive
hair loss in the puerperium is termed telogen flu vium.
• Weight Gain
Most of the normal weight gain in pregnancy is attributable to
the uterus and its contents, the breasts, and expanded blood and
extravascular extracellular fluid volumes. A smaller fraction results
from metabolic alterations that promote accumulation of cellular
water, fat, and protein, which are so-called maternal reserves. The
average weight gain during pregnancy approximates 1 2.5 kg or
27.5 Ib, and this value has remained consistent across studies and
over time (Hytten, 1 99 1 ; Jebeile, 20 1 6). Weight gain is consid­
ered in urther detail in Table 4-2 and in Chapter 9 (p. 1 65).
• Water Metabolism
In pregnancy, greater water retention is normal and mediated
in part by a drop in plasma osmolality of 1 0 mOsm/kg. This
decline develops in early pregnancy and is induced by a reset of
osmotic thresholds for thirst and vasopressin secretion (Fig. 4-3)
METABOLIC CHANGES
In response to the greater demands of the rapidly growing
fetus and placenta, the pregnant woman undergoes metabolic
changes that are numerous and intense. By the third trimes­
ter, maternal basal metabolic rate rises by 20 percent com­
pared with that of the nonpregnant state (Berggren, 20 1 5 ) .
This rate grows b y a n additional 1 0 percent in women with a
twin gestation (Shinagawa, 2005) . Viewed another way, the
additional total pregnancy energy demand associated with
normal pregnancy approximates 77,000 kcal (World H ealth
Organization, 2004) . This is stratifi e d as 8 5 , 2 8 5 , and 475
kcal/d during the irst, second, and third trimester, respec­
tively (Table 4- 1 ) . Of note, Abeysekera and coworkers (20 1 6)
reported that women accrue fat mass during pregnancy
despite the increased total energy expenditure and without
signiicant change in energy intake. This suggests more ei­
cient energy storage.
TABLE 4-2. Wei g ht G a i n Based on Preg n a n cy-Rel ated
Components
Tissues and Fluids
Fetus
Placenta
Am n ion ic fl u id
Uterus
Brea sts
B l ood
Extrava scu l a r fl u id
Materna l stores (fat)
Total
Cumulative Increase in Weight (g)
10
20
30
40
Weeks Weeks Weeks Weeks
5
20
30
1 40
45
'1 00
0
310
650
Mod ified fro m Hytten, 1 99 1 .
3 00
1 70
350
320
1 80
600
30
2050
4000
1 500
430
750
600
360
1 300
80
3480
8500
3400
650
800
970
405
1 450
1 480
3 345
1 2,500
M ate rna l P hys i o l ogy
300
296
)
�
a
E
s
0
)
E
n
a
L
292
288
284
280
276
272
MP
MP
LMP
4
12
8
16
Weeks of pregnancy
FIGURE 4-3 Mean va l ues (black line) ± sta nd a rd deviations (blue
lines) for plasma osmol a l ity (Posm ) mea s u red at weekly i nterva l s i n
n i ne women from preconception t o 1 6 weeks. L M P last men­
strua l period; MP menstrual period. (Redrawn with perm ission
from Davison JM, D u n lop W: Re nal hemodyn a m ics and t u b u l a r
fu nction i n normal h u m a n preg nancy. Kidney I nt 1 8: 1 52, 1 980.)
=
=
(Davison, 1 98 1 ; Lindheimer, 200 1 ) . Relaxin and other hormones
are thought to play a role (Conrad, 20 1 3) .
At term, the water content o f the fetus, placenta, and amni­
onic luid approximates 3.5 L. Another 3.0 L accumulates from
expanded maternal blood volume and from uterus and breast
growth. Thus, the minimum amount of extra water that the
average woman accrues during normal pregnancy approximates
6.5 L. This corresponds to 1 4.3 lb.
Clearly demonstrable pitting edema of the ankles and legs
is seen in most pregnant women, especially at the end of the
day. This fluid accumulation, which may amount to a liter or
so, results from greater venous pressure below the level of the
uterus as a consequence of partial vena cava occlusion. A decline
in interstitial colloid osmotic pressure induced by normal preg­
nancy also favors edema late in pregnancy (0ian, 1 985).
Longitudinal studies of body composition show a progres­
sive accumulation of total body water and fat mass during
pregnancy. These two components as well as initial maternal
weight and weight gained during pregnancy are highly associ­
ated with neonatal birthweight (Lederman, 1 999; Mardones­
Santander, 1 998) . "Over-nourished" women are more likely
to deliver oversized neonates, even when glucose tolerant (Di
Benedetto, 20 1 2) .
• Protein Metabolism
The products of conception, the uterus, and maternal blood
are relatively rich in protein rather than fat or carbohydrate.
At term, the normally grown fetus and placenta together weigh
about 4 kg and contain approximately 500 g of protein, or
about half of the total pregnancy increase. The remaining 500 g
is added to the uterus as contractile protein, to the breasts
55
primarily in the glands, and to maternal blood as hemoglobin
and plasma proteins.
Amino acid concentrations are higher in the fetal than in the
maternal compartment and generally result from facilitated
transport across the placenta (Cleal, 2 0 1 1 ; Panitchob, 20 1 5).
This greater concentration is largely regulated by the placenta
through an incompletely understood process. In particular,
placental transport is variable for individuals and for diferent
amino acids. For example, tyrosine is a conditionally essential
amino acid in the preterm neonate but not in the fetus (Van
den Akker, 20 1 0, 20 1 1 ) . The placenta concentrates amino
acids into the fetal circulation and is also involved in protein
synthesis, oxidation, and transamination of some nonessential
amino acids (Galan, 2009) .
Maternal protein intake does not appear to be a critical deter­
minant for birthweight among well-nourished women (Chong,
20 1 5) . Still, recent data suggest that current recommendations
for protein intake may be too low. These guidelines are extrapo­
lated from nonpregnant adults and may underestimate actual
needs. Stephens and colleagues (20 1 5) prospectively analyzed
maternal protein intake and metabolism. They estimated aver­
age requirements of 1 .22 g/kg/d of protein for early pregnancy
and 1 . 52 g/kg/d for late pregnancy. These levels are higher than
the current recommendation of 0.88 g/kg/d. The daily require­
ments for dietary protein intake during pregnancy are discussed
in Chapter 9 (p. 1 67) .
• Carbohydrate Metabol ism
Normal pregnancy is characterized by mild fasting hypogly­
cemia, postprandial hyperglycemia, and hyperinsulinemia
(Fig. 4-4) . his elevated basal level of plasma insulin in normal
�
J
E
140 -�
- Nonpregnant (n = 8)
120
1 00
so
E
- Nonpregnant (n = 8)
Normal pregnant
(n = 8)
Insulin
250
_
200
1 50
;
:..
1 00
50
o ��
�
MEALS:
S AM
t
1 PM
t
6 PM
t
12 M
S AM
FIGURE 4-4 D i u r n a l changes in plasma g l ucose a n d i n s u l i n i n
normal late preg na ncy. (Redrawn from P h e l ps, 1 98 1 .)
56
Mate rnal Anatomy a n d P hys i o l ogy
pregnancy is associated with several unique responses to glu­
cose ingestion. Speciically, after an oral glucose meal, gravidas
demonstrate prolonged hyperglycemia and hyperinsulinemia
and a greater suppression of glucagon (Phelps, 1 98 1 ) . This can­
not be explained by an increased metabolism of insulin because
its half-life during pregnancy is not changed appreciably (Lind,
1 977) . Instead, this response relects a pregnancy-induced state
of peripheral insulin resistance, which ensures a sustained post­
prandial supply of glucose to the fetus. Indeed, insulin sensitiv­
ity in late normal pregnancy is 30 to 70 percent lower than that
of nonpregnant women (Lowe, 20 1 4) .
The mechanisms responsible for this reduced insulin sensi­
tivity include numerous endocrine and inlammatory factors
(Angueira, 20 1 5) . In particular, pregnancy-related hormones
such as progesterone, placentally derived growth hormone, pro­
lactin, and cortisol; cytokines such as tumor necrosis factor; and
hormones derived from central adiposity, particularly leptin and
its interplay with prolactin, all have a role in the insulin resistance
of pregnancy. Even so, insulin resistance is not the only factor to
elevate postprandial glucose values. Hepatic gluconeogenesis is
augmented during both diabetic and nondiabetic pregnancies,
particularly in the third trimester (Angueira, 20 1 5) .
Overnight, the pregnant woman changes from a postpran­
dial state characterized by elevated and sustained glucose levels
to a fasting state characterized by decreased plasma glucose and
some amino acids. Plasma concentrations of free fatty acids,
triglycerides, and cholesterol are also higher in the fasting state.
his pregnancy-induced switch in fuels from glucose to lipids
has been called accelerated starvation. Certainly, when fasting is
prolonged in the pregnant woman, these alterations are exag­
gerated and ketonemia rapidly appears.
• Fat Metabolism
he concentrations of lipids, lipoproteins, and apolipopro­
teins in plasma rise appreciably during pregnancy (Appendix,
p. 1 259). Increased insulin resistance and estrogen stimulation
during pregnancy are responsible for the maternal hyperlipid­
emia. Augmented lipid synthesis and food intake contribute
to maternal fat accumulation during the fi r st two trimesters
(Herrera, 20 1 4) . In the third trimester, however, fat storage
declines or ceases. his is a consequence of enhanced lipolytic
activity, and decreased lipoprotein lipase activity reduces circu­
lating triglyceride uptake into adipose tissue. his transition to
a catabolic state favors maternal use of lipids as an energy source
and spares glucose and amino acids for the fetus.
Maternal hyperlipidemia is one of the most consistent and
striking changes of lipid metabolism during late pregnancy.
Triacylglycerol and cholesterol levels in very-low-density lipo­
proteins (VLDLs) , low-density lipoproteins (LDLs), and high­
density lipoproteins (HDLs) are increased during the third
trimester compared with those in nonpregnant women. During
the third trimester, the average level of total serum cholesterol
is 267 ± 30 mg/dL, of LDL-C is 1 36 ± 33 mg/dL, of H DL-C
is 8 1 ± 1 7 mg/dL, and of triglycerides is 245 ± 73 mg/dL
(Lippi, 2007) . After delivery, the concentrations of these lipids,
lipoproteins, and apolipoproteins decline. Breastfeeding drops
maternal triglyceride levels but increases those of HDL-C. The
efects of breastfeeding on total cholesterol and LDL-C levels
are unclear (Gunderson, 20 1 4) .
Hyperlipidemia i s theoretically a concern because it is
associated with endothelial dysfunction. From studies, how­
ever, endothelium-dependent vasodilation responses actually
improve across pregnancy (Saarelainen, 2006) . Ihis is partly
because increased HDL-C concentrations likely inhibit LDL
oxidation and thus protect the endothelium. hese indings
suggest that the increased cardiovascular disease risk in mul­
tiparas may be related to factors other than maternal hypercho­
lesterolemia.
Lept i n
This peptide hormone i s primarily secreted b y adipose tissue
in nonpregnant humans. It plays a key role in body fat and
energy expenditure regulation and in reproduction. For exam­
ple, leptin is important for implantation, cell proliferation, and
angiogenesis (Vazquez, 2 0 1 5). Leptin deiciency is associated
with anovulation and infertility, whereas certain leptin muta­
tions cause extreme obesity (Tsai, 20 1 5) .
Among normal-weight pregnant women, serum leptin lev­
els rise and peak during the second trimester and plateau until
term in concentrations two to four times higher than those in
nonpregnant women. Among obese women, leptin levels cor­
relate with adiposity (Ozias, 20 1 5 ; Tsai, 20 1 5) . In all cases,
leptin levels fall after delivery, relecting the significant amounts
produced by the placenta (Vazquez, 20 1 5) .
Leptin participates i n regulating energy metabolism dur­
ing pregnancy. Interestingly, despite the rise in leptin concen­
trations during pregnancy, reduced leptin sensitivity to food
intake during pregnancy has been described (Chehab, 20 1 4;
Vazquez, 20 1 5) . This "leptin resistance" may serve to promote
energy storage during pregnancy and for later lactation.
Higher leptin levels during pregnancy may be disadvanta­
geous under certain situations, such as in maternal obesity.
Leptin functions as a proinflammatory cytokine in white adi­
pose tissue, which may dysregulate the inlammatory cascade
and lead to placental dysfunction in obese women (Vazquez,
20 1 5) . In addition, abnormally elevated leptin levels have been
associated with preeclampsia and gestational diabetes (Bao,
20 1 5; Taylor, 20 1 5) .
Fetal leptin i s important for the development o f several
organs that include the pancreas, kidney, heart, and brain.
Fetal levels correlate with maternal body mass index (BMI) and
birthweight. Lower levels are linked to fetal-growth restriction
(Brifa, 20 1 5 ; Tsai, 20 1 5) .
Other Ad i pocyto k i nes
Dozens of hormones with metabolic and/or inflammatory
functions are produced by adipose tissue. Adiponectin is a pep­
tide produced primarily in maternal fat but not in the placenta
(Haghiac, 20 1 4) . Adiponectin levels inversely correlate with
adiposity, and it acts as a potent insulin sensitizer. Despite
reduced adiponectin levels in women with gestational diabetes,
directed assays are not useful for predicting diabetes develop­
ment (Hauguel-de Mouzon, 20 1 3) .
Ghrelin i s a peptide secreted principally b y the stomach in
response to hunger. It cooperates with other neuroendocrine
Maternal P h ys i o l ogy
factors, such as leptin, in energy homeostasis modulation.
Ghrelin is also expressed in the placenta and likely has a role
in fetal growth and cell proliferation (Gonzalez-Dominguez,
20 1 6) . Angelidis and associates (20 1 2) have reviewed the many
functions of ghrelin in the regulation of reproductive function.
Viatin is a peptide that was first identified as a growth fac­
tor for B lymphocytes, but it is mainly produced within adipose
tissue. Mumtaz and colleagues (20 1 5) propose that elevated
levels of visfatin and leptin impair uterine contractility. Such
findings may provide a physiological basis for the observation
that maternal obesity raises the risk for dysfunctional labor.
• Electrolyte and Minera l Metabolism
During normal pregnancy, nearly 1 000 mEq of sodium and 300
mEq ofpotassium are retained (Lindheimer, 1 987) . Although the
glomerular filtration rate of sodium and potassium is increased,
the excretion of these electrolytes is unchanged during preg­
nancy as a result of enhanced tubular resorption (Brown, 1 986,
1 988) . Although total accumulations of sodium and potassium
are elevated, their serum concentrations are diminished slightly
(Appendix, p. 1 257) . Several mechanisms may explain these
lower levels (Odutayo, 20 1 2) . In the case of potassium, it pos­
sibly involves the expanded plasma volume of pregnancy. With
respect to sodium, osmoregulation is altered and the threshold
for arginine vasopressin release is lowered. his promotes free
water retention and diminished sodium levels.
Total serum calcium levels, which include both ionized and
nonionized calcium, decrease during pregnancy. his reduction
follows lowered plasma albumin concentrations and in turn a
consequent decline in the amount of circulating protein-bound
nonionized calcium. Serum ionized calcium levels, however,
remain unchanged (Olausson, 20 1 2) .
h e developing fetus imposes a significant demand on
maternal calcium homeostasis. For example, the fetal skeleton
accretes approximately 30 g of calcium by term, 80 percent
of which is deposited during the third trimester. his demand
is largely met by a doubling of maternal intestinal calcium
absorption mediated partly by 1 ,25-dihydroxyvitamin D 3 •
hese higher levels of vitamin D are possibly stimulated by a
twofold rise in PTH-related peptide levels produced by several
tissues including the placenta (Kovacs, 2006; Olausson, 20 1 2) .
To help compensate, dietary intake o f suicient calcium i s nec­
essary to prevent excess depletion from the mother. A list of all
recommended daily allowances is found in Table 9-5 (p. 1 67) .
his is especially important for pregnant adolescents, in whom
bones are still developing. Unfortunately, a lack of robust data
prevents drawing firm conclusions regarding the utility of cal­
cium and vitamin D supplements during pregnancy (De-Regil,
20 1 6) .
Serum manesium levels also decline during pregnancy.
Bardicef and colleagues ( 1 995) concluded that pregnancy is
actually a state of extracellular magnesium depletion. Com­
pared with nonpregnant women, both total and ionized mag­
nesium concentrations are significantly lower during normal
pregnancy (Rylander, 20 1 4) .
Serum phosphate levels lie within the nonpregnant range
(Larsson, 2008) . Although calcitonin is an important
regulator of serum calcium and phosphate, the importance
of calcitonin as it relates to pregnancy is poorly understood
(Olausson, 20 1 2) .
Iodine requirements increase during normal pregnancy for sev­
eral reasons (Moleti, 20 14; Zimmermann, 20 1 2) . First, maternal
thyroxine production rises to maintain maternal euthyroidism
and to transfer thyroid hormone to the fetus prior to fetal thyroid
functioning. Second, fetal thyroid hormone production increases
during the second half of pregnancy. This contributes to greater
maternal iodine requirements because iodide readily crosses the
placenta. hird, the primary route of iodine excretion is through
the kidney. Beginning in early pregnancy, the iodide glomerular
iltration rate increases by 30 to 50 percent. In sum, because of
greater thyroid hormone production, fetal iodine requirements,
and augmented renal clearance, dietary iodine needs are higher
during normal gestation. lthough the placenta has the ability
to store iodine, whether this organ functions to protect the fetus
from inadequate maternal dietary iodine is currently unknown
(Burns, 20 1 1 ) . Iodine deiciency is discussed later in this chapter
(p. 7 1 ) and in Chapter 58 (p. 1 1 26) . At the other extreme, mater­
nal supplements containing excessive iodine have been associated
with congenital hypothyroidism. his stems from autoregulation
in the thyroid gland-known as the Wof-Chaikof fect-to
curb thyroxine production in response to iodide overconsump­
tion (Connelly, 20 12) .
With respect to most other minerals, pregnancy induces
little change in their metabolism other than their retention in
amounts equivalent to those needed for growth. An impor­
tant exception is the considerably greater requirement for iron,
which is discussed subsequently.
HEMATOLOGICAL CHANGES
• Blood Volume
he well-known hypervolemia associated with normal preg­
nancy averages 40 to 45 percent above the nonpregnant blood
volume after 32 to 34 weeks' gestation (Pritchard, 1 965;
Zeeman, 2009) . In individual women, expansion varies con­
siderably. In some, accumulated volume rises only modestly,
whereas in others blood volume nearly doubles. A fetus is not
essential, as augmented blood volume develops in some with
hydatidiform mole.
Pregnancy-induced hypervolemia serves several functions.
First, it meets the metabolic demands of the enlarged uterus
and its greatly hypertrophied vascular system. Second, it pro­
vides abundant nutrients and elements to support the rapidly
growing placenta and fetus. Third, the expanded intravascu­
lar volume protects the mother, and in turn the fetus, against
the deleterious efects of impaired venous return in the supine
and erect positions. Last, it safeguards the mother against the
adverse efects of parturition-associated blood loss.
Maternal blood volume begins to accrue during the irst
trimester. By 1 2 menstrual weeks, plasma volume expands by
approximately 1 5 percent compared with that prior to preg­
nancy (Bernstein, 200 1 ) . Maternal blood volume grows most
rapidly during the midtrimester, rises at a much slower rate
during the third trimester, and reaches a plateau during the last
57
58
Maternal Anatomy and P hysi o logy
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Gestational age (weeks)
36
12 weeks
postpartum
FIGURE 4-5 Blood vol ume expa nsion d u ri ng preg n a ncy in twi n s
( n 1 0) a nd s i n g l etons (n 40). Data shown as med ia ns. (Data
from Thomsen, 1 994.)
=
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Menses
:
Twin p regnancy
• Singleton pregnancy
•
3.5
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Second
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Third
Postpartum
Trimester
FIGURE 4-6 Estimated d a i ly i ron req u i rements d u ri ng preg n a ncy
in a 5 5-kg woma n . (Modified from Koenig, 20 1 4.)
=
several weeks of pregnancy (Fig. 4-5 ) . Blood volume accrues
even more dramatically in twin gestations. During blood vol­
ume expansion, plasma volume and erythrocyte number rise.
Although more plasma than erythrocytes is usually added to
the maternal circulation, the increase in erythrocyte volume is
considerable and averages 450 mL (Pritchard, 1 960) . Moder­
ate erythroid hyperplasia develops in the bone marrow, and the
reticulocyte count is elevated slightly during normal pregnancy.
These changes are almost certainly related to an elevated mater­
nal plasma erythropoietin level.
Hemog lobi n Co ncentrati o n a n d Hematocrit
Because of great plasma augmentation, both hemoglobin concen­
tration and hematocrit decline slightly during pregnancy (Appen­
dix, p. 1 25 5) . s a result, whole blood viscosity decreases (Huisman,
1 987). Hemoglobin concentration at term averages 1 2. 5 g/dL,
and in approximately 5 percent of women it is below 1 1 .0 g/dL.
Thus, a hemoglobin concentration below 1 1 .0 g/dL, especially
late in pregnancy, is considered abnormal and usually due to iron­
deficiency anemia rather than pregnancy hypervolemia.
• Iron Metabolism
The total iron content of normal adult women ranges from 2.0
to 2 . 5 g, or approximately half that found normally in men.
Most of this is incorporated in hemoglobin or myoglobin, and
thus, iron stores of normal young women only approximate
300 mg (Pritchard, 1 964) . Although the lower iron levels in
women may be partly due to menstrual blood loss, other fac­
tors have a role, particularly hepcidin-a peptide hormone that
functions as a homeostatic regulator of systemic iron metabo­
lism. Hepcidin levels rise with inlammation, but drop with
iron deficiency and several hormones, including testosterone,
estrogen, vitamin D, and possibly prolactin (Uu, 20 1 6; Wang,
20 1 5). Lower hepcidin levels are associated with greater absorp­
tion of iron via ferroportin in enterocytes (Camaschella, 20 1 5) .
I ro n Req u i rem ents
Of the approximate 1 000 mg of iron required for normal preg­
nancy, about 300 mg is actively transferred to the fetus and
placenta, and another 200 mg is lost through various normal
excretion routes, primarily the gastrointestinal tract. These
are obligatory losses and accrue even when the mother is iron
deficient. The average increase in the total circulating erythro­
cyte volume-about 450 mL-requires another 500 mg. Recall
that each 1 mL of erythrocytes contains 1 . 1 mg of iron.
As shown in Figure 4-6 , because most iron is used during
the latter half of pregnancy, the iron requirement becomes large
after midpregnancy and averages 6 to 7 mg/d (Pritchard, 1 970) .
In most women, this amount is usually not available from iron
stores or diet. Thus, without supplemental iron, the optimal
rise in maternal erythrocyte volume will not develop, and the
hemoglobin concentration and hematocrit will fall appreciably
as plasma volume rises. At the same time, fetal red cell produc­
tion is not impaired because the placenta transfers iron even if
the mother has severe iron-deficiency anemia. In severe cases,
we have documented maternal hemoglobin values of 3 gl dL,
and at the same time, fetuses had hemoglobin concentrations
of 1 6 gl dL. The mechanisms of placental iron transport and
regulation are complex (Koenig, 20 1 4; McArdle, 20 1 4) .
I f the nonanemic pregnant woman i s not given supplemental
iron, then serum iron and ferritin concentrations decline ater mid­
pregnancy. Importantly, hepcidin levels drop early in pregnancy
(Hedengran, 20 1 6; Koenig, 20 1 4) . s noted, lower hepcidin lev­
els aid iron transfer into the maternal circulation via ferroportin
in enterocytes. Lower hepcidin levels also augment iron transport
into the fetus via ferroportin in syncytiotrophoblast.
With normal vaginal delivery, 5 00 to 600 mL of blood is
typically lost, and thus not all the maternal iron added in the
form of hemoglobin is spent (Pritchard, 1 965). he excess
hemoglobin iron becomes stored iron.
• Immunological Functions
Pregnancy is associated with suppression of various humoral
and cell-mediated immunological functions (Chap. 5, p. 95).
his permits accommodation of the "foreign" semiallogeneic
fetal graft that contains antigens of both maternal and pater­
nal origin (Redman, 20 1 4) . he tolerance that exists at the
maternal-fetal interface remains a great unsolved medical mys­
tery. This tolerance is complex and involves certain immune
system adaptations and crosstalk among the maternal micro­
biome, uterine decidua, and trophoblast. In particular, areas of
M aternal Phys i o l ogy
the uterus that were previously considered sterile are colonized
with bacteria. In most cases, these microbes are believed to be
commensal and play a tolerizing and protective role. Indeed,
commensal organisms may inhibit the proliferation of certain
pathogens. Several reviewers have described these relationships
(Mor, 20 1 5 ; Racicot, 20 1 4; Sisti, 20 1 6) .
One immune adaptation that promotes tolerance and pro­
tection at the maternal-fetal interface involves the expression of
special major histocompatibility complex (MHC) molecules on
the trophoblast. Recall that all cells of the body express a "badge"
that identifies "self' and therefore privilege against attack by
immune responses. For most cells of the body, this "badge" is
known as MHC Class Ia. However, it is uncommon for two
unrelated individuals to share compatible MHC class Ia. This
creates a potential problem for reproduction because half of the
fetus is composed of paternally derived antigens. To circumvent
this problem, trophoblast cells express a form of MHC that does
not vary between individuals. This "nonclassic" MHC is known
as human leukocyte antigen class Ib and includes HLA-E, HLA­
F, and HLA-G. Recognition of these H LA class Ib proteins by
natural killer cells residing within the decidua inhibits their activ­
ity and promotes immune quiescence (Djurisic, 20 1 4) .
Another immune adaptation that promotes tolerances stems
from important changes in CD4 T lymphocyte subpopulations
in pregnancy. First, Th 1 -mediated immunity shifts to h2-medi­
ated immunity. Indeed, an important antiinlammatory compo­
nent of pregnancy involves suppression of T-helper (Th) 1 and
T-cytotoxic (Tc) 1 cells, which lower secretion of interleukin-2
(IL-2) , interferon-a, and tumor necrosis factor (TNF) . More­
over, suppressed Th 1 response is thought to be a requisite for
pregnancy continuation. It also may explain pregnancy-related
remission of some autoimmune disorders such as rheumatoid
arthritis, multiple sclerosis, and Hashimoto thyroiditis-which
are cell-mediated immune diseases stimulated by h1 cyto­
kines (Kumru, 2005) . With suppression of Th 1 cells, there is
upregulation of Th2 cells to increase secretion of IL-4, IL- 1 0,
and IL- 1 3 (Michimata, 2003). hese h2 cytokines promote
humoral, or antibody-based, immunity. hus, autoimmune dis­
eases mediated mainly by autoantibodies, such as systemic lupus
erythematosus, may lare if the disease is already active in early
pregnancy. But, the transition to an antibody-mediated immu­
nity is an important defense during pregnancy and early puerpe­
rium. In cervical mucus, peak levels of immunoglobulins A and
G (IgA and IgG) are significantly higher during pregnancy, and
the immunoglobulin-rich cervical mucus plug creates a barrier
to ascending infection (Hansen, 20 1 4; Wang, 20 1 4) . Similarly,
IgG is transferred to the developing fetus in the third trimes­
ter as a form of passive immunity, ostensibly in anticipation
of birth. Further, immunoglobulins secreted into breast milk
during lactation augment neonatal defenses against infection.
Other subpopulations of CD4 T lymphocytes serve muco­
sal and barrier immunity. These specifi c CD4-positive cells are
known as h 1 7 cells and Treg cells. h 1 7 cells are proinflam­
matory and express the cytokine I L- 1 7 and the retinoic acid
receptor-related orphan receptors (RORs) . Treg cells express
the transcription factor forkhead box protein-3 (FOXP3) and
confer tolerizing activity. here is a shift toward Treg CD4 cells
in the first trimester, which peaks during the second trimester
and falls toward delivery (Figueiredo, 20 1 6) . his shift may
promote tolerance at the maternal-fetal interface (La Rocca,
20 1 4) . In particular, failure of these CD4 T lymphocyte sub­
population alterations may be related to preeclampsia develop­
ment (Vargas-Rojas, 20 1 6) .
• leukocytes a n d lymphocytes
Normal leukocyte counts during pregnancy can be higher than
nonpregnant values, and upper values approach 1 5 ,000/jLL
(Appendix, p. 1 255) . During labor and the early puerpe­
rium, values may become markedly elevated, attaining levels
of 25 ,000/LL or greater. The cause is unknown, but the same
response occurs during and after strenuous exercise. The leuko­
cytosis possibly represents the reappearance of leukocytes previ­
ously shunted out of active circulation.
The distribution of lymphocyte cell types is also altered
during pregnancy. Speciically, B lymphocytes numbers are
unchanged, but the absolute numbers of T lymphocytes rise
and create a relative increase. Concurrently, the ratio of CD4 to
CD8 T lymphocytes does not change (Kuhnert, 1 998) .
I nfla m matory Ma rkers
Many tests performed to diagnose inlammation cannot be
used reliably during pregnancy. For example, leukocyte alka­
line phosphatase levels-used to evaluate myeloproliferative
disorders-are elevated beginning early in pregnancy. he
concentration of C-reactive protein, an acute-phase serum reac­
tant, rises rapidly in response to tissue trauma or infl a mmation.
Median C-reactive protein levels in pregnancy and labor are
higher than for nonpregnant women (Anderson, 2 0 1 3 ; Watts,
1 99 1 ) . Of nonlaboring gravidas, 95 percent had levels of
1 . 5 mg/ dL or less, and gestational age did not afect serum lev­
els. Another marker of inlammation, the erythrocyte sedimenta­
tion rate (ESR), is increased in normal pregnancy because of
elevated plasma globulins and ibrinogen levels. Complement
actors C3 and C4 levels also significantly rise during the sec­
ond and third trimesters (Gallery, 1 98 1 ; Richani, 2005) . Last,
concentrations of procalcitonin, a normal precursor of calcito­
nin, increase at the end of the third trimester and through the
irst few postpartum days. Procalcitonin levels rise with severe
bacterial infections but remain low in viral infections and non­
specifi c inlammatory disease. However, measured levels poorly
predict development of overt or subclinical chorioamnionitis
after premature rupture of membranes (Thornburg, 20 1 6) .
• Coagulation and Fibrinolysis
During normal pregnancy, both coagulation and fibrinolysis are
augmented but remain balanced to maintain hemostasis (Kenny,
20 1 4) . Evidence of activation includes increased concentrations
of all clotting factors except factors I and III (Table 4-3 ) .
O f procoagulants, the level and rate o f thrombin generation
throughout gestation progressively increase (McLean, 20 1 2) . In
normal nonpregnant women, plasma ibrinogen (factor 1) aver­
ages 300 mg/dL and ranges from 200 to 400 mg/dL. During nor­
mal pregnancy, the fibrinogen concentration rises approximately
50 percent. In late pregnancy, it averages 450 mg/dL, with a
range from 300 to 600 mg/dL. his contributes greatly to
59
60
Maternal Anatomy a n d P hys i o l ogy
TABLE 4-3. Changes i n M ea su res of Hemosta s i s D u ri n g
N o r m a l Preg n a ncy
Parameter
Activated PlT (sec)
F i b r i n og e n (mg/d L)
Factor VI I (%)
Factor X (%)
P l as m i nogen (%)
tPA (ng/mL)
Antit h ro m b i n I I I (%)
P rote i n C (%)
Tota l p rote i n S (%)
Non preg nant
3 1 .6 ± 4.9
256 ± 58
Term Pregnant
3 1 .9 ± 2 .9
473 ± 72a
9 9 . 3 ± 1 9 .4
1 8 1 .4 ± 48.0a
97.7 ± 1 5 .4
1 44.5 ± 2 0. 1 a
1 05 .5 ± 1 4. 1
1 3 6.2 ± 1 9 .5a
5 . 7 ± 3 .6
98.9 ± 1 3 . 2
7 7 . 2 ± 1 2 .0
7 5 .6 ± 1 4.0
5.0 ± 1 .5
97.5 ± 3 3 . 3
6 2 . 9 ± 20.5a
49.9 ± 1 0 .2a
ap < .0 5 .
Data s h own as mean ± sta n d a rd d eviation.
PlT pa rtia l thromboplastin time; tPA = tissue plasm i nogen
activator.
Data fro m U c h i kova, 2005.
=
the striking increase in the ESR. Also, levels of factor XIII­
ibrin stabilizing oetor-signiicantly drop as normal pregnancy
advances (Sharief, 20 1 4) .
The end product o f the coagulation cascade i s ibrin for­
mation, and the main function of the fibrinolytic system is to
remove excess ibrin (Fig. 4 1 -29, p. 784) . Tissue plasminogen
activator (tPA) converts plasminogen into plasmin, which
causes ibrinolysis and produces ibrin-degradation products
such as D-dimers. Although somewhat conlicting, most evi­
dence suggests that fibrinolytic activity is reduced in normal
pregnancy (Kenny, 2 0 1 4) . As reviewed by Cunningham and
Nelson (20 1 5) , these changes favor ibrin formation. Although
this is countered by increased levels of plasminogen, the net
result is that pregnancy is a procoagulant state. Such changes
serve to ensure hemostatic control during normal pregnancy,
particularly during delivery when a certain amount of blood
loss is expected.
Reg u latory Prote i n s
Several proteins are natural inhibitors o f coagulation, includ­
ing proteins C and S and antithrombin (Fig. 52- I , p. 1 005) .
Inherited or acquired deficiencies of these and other natural
regulatory proteins-collectively referred to as thrombophilias­
account for many thromboembolic episodes during pregnancy.
hey are discussed in Chapter 52 (p. 1 006) .
Activated protein , along with the cofactors protein S and
factor V, functions as an anticoagulant by neutralizing the pro­
coagulants factor Va and factor VIlla. During pregnancy, resis­
tance to activated protein C grows progressively and is related
to a concomitant drop in free protein S levels and greater fac­
tor VIII concentrations. Between the irst and third trimesters,
activated protein C levels decline from 2.4 to 1 .9 V/mL, and
free protein S concentrations diminish from 0.4 to 0. 1 6 V/
mL (Cunningham, 20 1 5; Walker, 1 997) . Antithrombin levels
decrease by 1 3 percent between midpregnancy and term and
fall 30 percent from this baseline until 1 2 hours after delivery.
By 72 hours after delivery, there is a return to baseline Games,
20 1 4) .
Pl ate lets
Normal pregnancy promotes platelet changes. In one study,
the average platelet count declined slightly during pregnancy
to 2 1 3,OOO/1L compared with 250,000/1L in nonpregnant
controls (Boehlen, 2000) . hrombocytopenia deined as
below the 2.5th percentile corresponded to a platelet count of
1 1 6,OOO/1L. Lower platelet concentrations are partially due to
hemodilution. Also, platelet consumption is likely augmented
and creates a greater proportion of younger and therefore larger
platelets (Han, 20 1 4; Valera, 20 1 0) . Further, levels of several
markers of platelet activation rise with gestational age but drop
postpartum (Robb, 20 1 0) . Because of splenic enlargement,
there may be an element of "hypersplenism," in which platelets
are prematurely destroyed (Kenny, 20 1 4) .
• Spleen
By the end of normal pregnancy, the spleen enlarges by up to
50 percent compared with that in the irst trimester (Maymon,
2007) . Moreover, Gayer and coworkers (20 1 2) found that
splenic size was 68-percent greater compared with that of non­
pregnant controls. he cause of this splenomegaly is unknown,
but it might follow the increased blood volume and/or the
hemodynamic changes of pregnancy.
CARDIOVASCULAR SYSTEM
Changes in cardiac function become apparent during the irst
8 weeks of pregnancy (Hibbard, 20 1 4) . Cardiac output is
increased as early as the ifth week and reflects a reduced sys­
temic vascular resistance and an increased heart rate. Compared
with prepregnancy measurements, brachial systolic blood pres­
sure, diastolic blood pressure, and central systolic blood pressure
are all signiicantly lower 6 to 7 weeks from the last menstrual
period (Mahendru, 20 1 2) . he resting pulse rate rises approxi­
mately 10 beats/min during pregnancy. Nelson and associates
(20 1 5) found that for both normal and overweight women,
heart rate increased signiicantly between 12 and 16 weeks' and
between 32 and 36 weeks' gestation. Between weeks 10 and 20,
plasma volume expansion begins, and preload rises. his aug­
mented preload results in signiicantly larger left atrial volumes
and ejection fractions (Cong, 20 1 5) .
Ventricular performance during pregnancy is inluenced by
both the decrease in systemic vascular resistance and changes in
pulsatile arterial low. Multiple factors contribute to this overall
altered hemodynamic function, which allows the physiological
demands of the fetus to be met while maintaining maternal
cardiovascular integrity (Hibbard, 20 1 4) . hese changes during
the last half of pregnancy and efects of maternal posture are
summarized in Figure 4-7.
• Heart
As the diaphragm becomes progressively elevated, the heart
is displaced to the left and upward and is rotated on its long
axis. As a result, the apex is moved somewhat laterally from
its usual position and produces a larger cardiac silhouette in
chest radiographs. Furthermore, gravidas normally have some
degree of benign pericardial efusion, which may enlarge the
Matern a l Phys i o l ogy
95
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1 2-1 6
26-30
32-36
postpartum
weeks
weeks
weeks
FIGURE 4-7 Left ventric u l a r stroke vol u me across preg na ncy
compared with 1 2-week postpartum (non preg n a nt) va l ues for
norma l-weig ht women in the s u p i n e a nd latera l positions. (Data
from Nelson, 201 5.)
cardiac silhouette (Enein, 1 987) . These factors make it dii­
cult to precisely identiy moderate degrees of cardiomegaly by
simple radiographic studies.
Normal pregnancy induces characteristic electrocardio­
graphic changes, and the most common is slight left-axis devia­
tion due to the altered heart position. Q waves in leads II, III
and avF and lat or inverted T-waves in leads III, V1 -V3 may
also occur (Sunitha, 20 1 4) .
During pregnancy, many o f the normal cardiac souns are
modiied. hese include: ( 1 ) an exaggerated splitting of the irst
heart sound and increased loudness of both components, (2) no
deinite changes in the aortic and pulmonary elements of the
second sound, and (3) a loud, easily heard third sound (Cut­
forth, 1 966) . In 90 percent of gravidas, they also heard a sys­
tolic murmur that was intensiied during inspiration in some or
expiration in others and that disappeared shortly after delivery.
A soft diastolic murmur was noted transiently in 20 percent,
and continuous murmurs arising from the breast vasculature in
10 percent (Fig. 49- 1 , p. 950) .
Structurally, the expanding plasma volume seen during nor­
mal pregnancy is relected by enlarging cardiac end-systolic and
end-diastolic dimensions. Concurrently, however, septal thick­
ness or ejection fraction does not change. This is because the
dimensional changes are accompanied by substantive ventricu­
lar remodeling, which is characterized by left-ventricular mass
expansion of 30 to 35 percent near term. In the nonpregnant
state, the heart is capable of remodeling in response to stimuli
such as hypertension and exercise. Such cardiac plasticiy likely
is a continuum that encompasses physiological growth-such
as that in exercise, and pathological hypertrophy-such as with
hypertension (Hill, 2008) .
Stewart and colleagues (20 1 6) used cardiac MR imaging to
prospectively evaluate cardiac remodeling during pregnancy.
Compared with the first trimester, left ventricular mass increased
signiicantly beginning at 26 to 30 weeks' gestation, and this
continued until delivery (Fig. 4-8) . This remodeling is concen­
tric and proportional to maternal size for both normal and over­
weight women and resolved within 3 months of delivery.
Certainly for clinical purposes, ventricular unction during
pregnancy is normal, as estimated by the Braunwad ventricuar
unction graph (Fig. 4-9) . For the given illing pressures, cardiac
I
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)
>
1 20
1 10
•
•
Normal weight
Overweight
1 00
90
80
70
Nonpregnant 1 2-1 6
( postpartum) weeks
26-30
weeks
32-36
weeks
Delivery
FIGURE 4-8 Let ventricu l a r mass of norma l-weight a nd over­
weight women across p reg na ncy com pared with 1 2-week postpa r­
t u m (nonpreg n a nt) va l ues. (Data from Stewart, 20 1 6.)
output is appropriate and thus cardiac unction during pregnancy
is eudynamic. Of the metabolic changes that occur in the heart
during pregnancy, the eiciency of cardiac work-which is the
product of cardiac output X mean arterial pressure-is estimated
to rise by approximately 25 percent. The associated increase in
oxygen consumption is primarily accomplished via increased
coronary blood low rather than increased extraction (Liu, 20 1 4) .
• Card iac Output
When measured in the lateral recumbent position at rest, car­
diac output increases signiicantly beginning in early pregnancy.
It continues to rise and remains elevated during the remainder
of pregnancy. In a supine woman, a large uterus rather consis­
tently compresses veins and diminishes venous return from the
lower body. It also may compress the aorta (Bieniarz, 1 968) .
In response, cardiac illing may be reduced and cardiac o utput
1 20
110
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1 00
90
Normal
80
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60
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50
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>
Hyperdynamic
70
30
-o f: e
40
o
i
5
i
Depressed
i
I
10
15
20
PCWP ( m m Hg)
i
25
30
FIGURE 4-9 Relationship between let ventricu l a r stroke work
i ndex (LVSWI), cardiac output, and p u l monary cap i l l a ry wedge pres­
s u re (PCWP) in 1 0 normal preg n a nt women in the third trimester.
(Data from Cla rk, 1 989.)
61
62
Mater n a l A n atomy and Physi o l ogy
TABLE 4-4. Centra l H emodyn a m i c Cha nges i n 1 0 N o r m a l N u l l i pa rous Women Nea r Term a n d
Postpa rt u m
Preg na nta
(35-38 wk)
Mea n a rterial p ress u re ( m m Hg)
P u l m o n a ry capi l l a ry wedge pressu re (m m Hg)
Centra l venous pres s u re (mm Hg)
Heart rate (beats/m i n)
Card iac output (L/m i n)
System ic vasc u l a r resi sta n ce (dyn/sec/cm-S )
P u l m o n a ry vascu l a r resi sta nce (dyn/sec/cm- S )
Seru m col l o i d o s m otic p ress u re ( m m Hg)
COP-PCWP g rad ient (mm Hg)
Let ventri c u l a r stroke work i n d ex (g/m/m 2 )
90
8
4
83
6.2
1 21 0
78
1 8.0
1 0.5
48
±
±
±
±
±
±
±
±
±
±
6
2
3
10
1 .0
266
22
1 .5
2.7
6
Postpartum
( 1 1 - 1 3 wk)
Change b
86 ± 8
6 ± 2
4 ± 3
71 ± 10
4.3 ± 0.9
1 5 30 ± 520
1 1 9 ± 47
20.8 ± 1 .0
1 4.5 ± 2.5
41 ± 8
NSC
N SC
NSC
+ 1 7%
+43%
-21 %
- 34%
- 1 4%
- 28%
N SC
aMea s u red i n latera l rec u m bent position.
bChanges sig n ificant u n less N SC = no s i g n ifica nt c h a nge.
COP = col lo i d o s m otic p ressu re; PCWP = p u l m o na ry ca p i l la ry wedge pressu re.
Data from Cla r k, 1 989.
lessened. Speciically, cardiac MR imaging shows that when a
woman rolls from her back onto her left side, cardiac output
at 26 to 30 weeks' gestation rises by approximately 20 percent
and at 32 to 34 weeks by 1 0 percent (Nelson, 20 1 5) . Con­
sistent with this, Simpson and James (2005) found that fetal
oxygen saturation is approximately 1 0 percent higher if a labor­
ing woman lies in a lateral recumbent position compared with
supine. Upon standing, cardiac output falls to the same degree
as in the nonpregnant woman (Easterling, 1 988).
In multifetal pregnancies, compared with singletons, mater­
nal cardiac output is augmented further by almost another 20
percent. Ghi and coworkers (20 1 5) used transthoracic echo­
cardiography to show that irst-trimester cardiac output with
twins (mean 5 . 50 Umin) was more than 20 percent greater
than postpartum values. Cardiac output values in the second
(6. 3 1 L/min) and third (6.29 Umin) trimesters were increased
an additional 1 5 percent compared with irst-trimester output.
Left atrial and left ventricular end-diastolic diameters are also
longer with twins due to augmented preload (Kametas, 2003) .
The greater heart rate and inotropic contractility imply that car­
diovascular reserve is reduced in multifetal gestations.
D uring first-stage labor, cardiac output rises moderately.
During the second stage, with vigorous expulsive eforts, it
is appreciably greater. The pregnancy-induced increase is lost
ater delivery, at times dependent on blood loss.
appreciably. Thus, although cardiac output rises, left ventricular
function as measured by stroke work index remains similar to
the nonpregnant normal range (see Fig. 4-9) . Put another way,
normal pregnancy is not a continuous "high-output" state.
• Hemodynamic Function in Late Pregnancy
m
Clark and associates ( 1 989) conducted invasive studies to mea­
sure hemodynamic function late in pregnancy (Table 4-4) .
Right heart catheterization was performed i n 1 0 healthy nul­
liparas at 35 to 38 weeks' gestation, and again at 1 1 to 13 weeks
postpartum. Late pregnancy was associated with the expected
increases in heart rate, stroke volume, and cardiac output. Sys­
temic vascular and pulmonary vascular resistance both dropped
signiicantly, as did colloid osmotic pressure. Pulmonary capil­
lary wedge pressure and central venous pressure did not change
• Circulation and Blood Pressure
Changes in posture afect arterial blood pressure (Fig. 4- 1 0) .
Brachial artery pressure when sitting is lower than that when in
the lateral recumbent supine position (Bamber, 2003) . Addi­
tionally, systolic blood pressure is lower in the lateral positions
compared with either the flexed sitting or supine positions
(Armstrong, 20 1 1 ) . Arterial pressure usually declines to a nadir
at 24 to 26 weeks' gestation and rises thereafter. Diastolic pres­
sure decreases more than systolic.
1 20
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90
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1 00
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80
E
)
)
)
g
0
Supine
----
T_�
T..
-..
I_..
T_
. _
I_..
.
V /
�
..
.
T �
SYSTOLIC
_
Left lateral recumbent
---
70
-�-.
DIASTOLIC
60
50
40
o
'
o
4
8
12
1 6 20 24 28 32
Gestation (weeks)
36
,I -.
40
PP
FIGURE 4-1 0 Seq uential changes (±SEM) in b lood press u re
t h ro u g hout p reg nancy in 69 women i n su pine (blue lines) and left
l atera l recu m bent positions (red lines). PP postpart u m . (Ada pted
fro m Wi l son, 1 980.)
=
M aternal Phys i o l ogy
Morris and associates (20 1 5) studied measures of vas­
cular compliance before pregnancy, during pregnancy, and
postpartum. Compared with healthy nonpregnant controls,
signiicant declines in mean arterial pressure and arterial
stifness, measured using pulse wave velocity, were observed
between the prepregnant and the postpartum time periods.
These indings suggest that pregnancy confers a favorable
efect on maternal cardiovascular remodeling and may pos­
sibly help explain why the risk of preeclampsia is reduced in
subsequent pregnancies.
Antecubital venous pressure remains unchanged during
pregnancy. In the supine position, however, femoral venous
pressure rises steadily, from approximately 8 mm Hg early
in pregnancy to 24 mm Hg at term. Venous blood flow in
the legs is retarded during pregnancy except when the lateral
recumbent position is assumed (Wright, 1 950) . his tendency
toward blood stagnation in the lower extremities during later
pregnancy is attriburable to occlusion of the pelvic veins and
inferior vena cava by the enlarged uterus. he elevated venous
pressure returns to normal when the pregnant woman lies on
her side and immediately after delivery (McLennan, 1 943) .
These alterations contribute to the dependent edema frequently
experienced and to the development of varicose veins in the legs
and vulva, as well as hemorrhoids. These changes also predis­
pose to deep-vein thrombosis.
S u p i n e Hypotension
In approximately 1 0 percent of women, supine compression
of the great vessels by the uterus causes signiicant arterial
hypotension, sometimes referred to as the supine hypotensive
syndrome (Kinsella, 1 994) . Also when supine, uterine arterial
pressure-and thus uterine blood flow-is signiicantly lower
than that in the brachial artery. Evidence to support whether
this directly afects fetal heart rate patterns in uncomplicated
low-risk pregnancies is conlicting (Armstrong, 20 1 1 ; Ibrahim,
20 1 5 ; Tamas, 2007) . Similar changes can also be seen with
hemorrhage or with spinal analgesia.
• Renin, Angiotensin II, and Plasma Volume
The renin-angiotensin-aldosterone axis is intimately involved
in blood pressure control via sodium and water balance. All
components of this system show increased levels in normal
pregnancy. Renin is produced by both the maternal kidney
and the placenta, and greater amounts of renin substrate
(angiotensinogen) are produced by both maternal and fetal
liver. Elevated angiotensinogen levels result, in part, from
augmented estrogen production during normal pregnancy
and are important in irst-trimester blood pressure mainte­
nance (Lumbers, 20 1 4) .
Gant and associates ( 1 973) reported that nulliparas who
remained normotensive became and stayed refractory to the
pressor efects of infused angiotensin II. Conversely, those
who ultimately became hypertensive developed, but then lost,
this refractoriness. The diminished vascular responsiveness to
angiotensin II may be progesterone related. Normally, preg­
nant women lose their acquired vascular refractoriness to angio­
tensin II within 1 5 to 30 minutes after the placenta is delivered.
Large amounts of intramuscular progesterone given during late
labor delay this diminishing refractoriness.
• Cardiac Natriuretic Peptides
At least two species of these atrial natriuretic peptide (ANP)
and brain natriuretic peptide (BNP)-are secreted by cardiomy­
ocytes in response to chamber-wall stretching. These peptides
regulate blood volume by provoking natriuresis, diuresis, and
vascular smooth-muscle relaxation. In nonpregnant and preg­
nant patients, levels of BNP and of amino-terminal pro-brain
natriuretic peptide (Nt pro-BNP) , as well as newer analytes
such as suppressor of tumorigenicity 2 (ST2) , may be useful
in screening for depressed left ventricular systolic function
and determining chronic heart failure prognosis (Ghashghaei,
20 1 6) .
During normal pregnancy, plasma ANP and B N P levels are
maintained in the nonpregnant range despite greater plasma
volume (Yurteri-Kaplan, 20 1 2) . In one study, median BNP
levels were stable across pregnancy with values < 20 pg/mL
(Resnik, 2005) . BNP levels are increased in severe preeclamp­
sia, and this may be caused by cardiac strain from increased
afterload (Afshani, 20 1 3) . It would appear that ANP-induced
physiological adaptations participate in extracellular fl u id vol­
ume expansion and in the elevated plasma aldosterone concen­
trations characteristic of normal pregnancy.
-
• Prostaglandins
Elevated prostaglandin production during pregnancy is thought
to have a central role in control of vascular tone, blood pres­
sure, and sodium balance. Renal medullary prostaglandin E2
synthesis is markedly elevated during late pregnancy and is
presumed to be natriuretic. Levels of prostacyclin (PGI 2 ) , the
principal prostaglandin of endothelium, also rise during late
pregnancy. PGI 2 regulates blood pressure and platelet function.
It helps maintain vasodilation during pregnancy, and its dei­
ciency is associated with pathological vasoconstriction (Shah,
20 1 5) . Thus, the ratio of PGI 2 to thromboxane in maternal
urine and blood is considered important in preeclampsia patho­
genesis (Majed, 20 1 2) .
• Endothelin
Several endothelins are generated in pregnancy. Endothelin- 1
is a potent vasoconstrictor produced in endothelial and vas­
cular smooth muscle cells and regulates local vasomotor tone
(George, 20 1 1 ; Lankhorst, 20 1 6) . Its production is stimulated
by angiotensin II, arginine vasopressin, and thrombin. Endo­
thelins, in turn, stimulate secretion of ANP, aldosterone, and
catecholamines. Vascular sensitivity to endothelin- 1 is not
altered during normal pregnancy. Pathologically elevated levels
may play a role in preeclampsia (Saleh, 20 1 6) .
• Nitric Oxide
This potent vasodilator is released by endothelial cells and may
modiy vascular resistance during pregnancy. Moreover, nitric
oxide is an important mediator of placental vascular tone and
63
64
Mate rna l A n atomy a n d Physiology
develop ment (Krause, 20 1 1 ; Kulandavelu, 20 1 3) . Abnormal
nitric oxide synthesis has been linked to preeclampsia develop­
ment (Laskowska, 20 1 5; Vignini, 20 1 6) .
RESPIRATORY TRACT
Of anatomic changes, the diaphragm rises approximately 4 cm
during pregnancy (Fig. 4- 1 1 ) . he subcostal angle widens
appreciably as the transverse diameter of the thoracic cage
lengthens approximately 2 cm. The thoracic circumference
increases about 6 cm, but not suiciently to prevent reduced
residual lung volumes created by the elevated diaphragm. Even
so, diaphragmatic excursion is greater in pregnant than in non­
pregnant women.
• Pulmonary Function
Decreased plasma osmolality also results in less respiratory
depression (Moen, 20 1 4) . his provides an additional mecha­
nism for the increased minute ventilation seen in pregnancy,
and one that is not dependent on progesterone.
Regarding pulmonary function, peak expiratory low rates
rise p rogressively as gestation advances (Grindheim, 20 1 2) .
Lung compliance i s unafected b y pregnancy. Airway conduc­
tance is increased and total pulmonary resistance reduced, possi­
bly as a result of progesterone. The maximum breathing capaciy
and orced or timed vital capaciy are not altered appreciably. It
is unclear whether the critical closing volume-the lung volume
at which airways in the dependent parts of the lung begin to
close during expiration-is higher in pregnancy (Hegewald,
20 1 1 ) . Pulmonary function with a singleton pregnancy does
not signiicantly difer from that with twins (MAulife, 2002;
Siddiqui, 20 1 4) . Importantly, the greater oxygen requirements
and perhaps the increased critical closing volume imposed by
pregnancy make respiratory diseases more serious.
Demir and colleagues (20 1 5) studied nasal physiology in 85
pregnant women. Although the minimal cross-sectional area
decreased between the irst and third trimesters, subjective reports
Of physiological lung changes, unctional residual capaciy (PRe)
decreases by approximately 20 to 30 percent or 400 to 700
mL during pregnancy (Fig. 4- 1 2) . his capacity is composed
of expiratory reserve volume-which drops 1 5 to 20 percent
or 200 to 300 mL-and residual
volume-which decreases 20 to
25 percent or 200 to 400 mL.
FRe and residual volume decline
progressively across pregnancy
due to diaphragm elevation. Sig­
niicant reductions are observed
by the sixth month. Inspiratory
capaciy, the maximum volume
" "
that can be inhaled from FRe,
,
"
,
"
"
rises by 5 to 1 0 percent or 200 to
/ 1 03.5° ""
350 mL during pregnancy. Total
,�
, , ,,- - - - .."" '
,
lung capaci-the combination
\
I
\
I
'
of FRe and inspiratory capac­
,
I
,
ity-is unchanged or decreases
�
Uterus
I
by less than 5 percent at term
. (37 weeks) I:
\
'
\
(Hegewald, 20 1 1 ) .
I
\
"
,'
,
The respiratory rate i s essen­
,
tially unchanged, but tidal
volume and resting minute ven­
tilation increase signiicantly
as pregnancy advances. Kolar­
zyk and coworkers (2005)
� is-7 e m
- .
reported significantly greater
..
,
.
,
.
mean tidal volumes-0.66 to
,
, \ \\
I
0 . 8 LI min-and resting min­
I
I
ute ventilations-1 0.7 to 1 4. 1
: --I
Llmin-compared with those
I
,
,
of nonpregnant women. The
\
\
elevated minute ventilation is
" �
caused by several factors. These
"
..
include
enhanced
respira­
< : : ::-- ---- --- toy drive primarily due to the
FIGURE 4-1 1 Chest wa l l measureme nts in n o n p reg n a nt (left) a nd preg n a nt women (right) . The
stimulatory action of proges­
s u bcosta l a n g le i ncreases, as does the a nteroposterior a nd tra n sverse d i a m eters of the chest wa l l
terone, low expiratory reserve
a nd chest wa l l circu mference. These c h a n ges compensate for t h e 4-cm elevation o f t h e d i a p h ra g m
volume, and compensated respi­
so t h a t tota l l u n g ca pacity is not s i g n ifica ntly red uced . (Redrawn from Hegewa ld MJ, Cra po RO:
ratory alkalosis (Heenan, 2003) .
Respi ratory physiology in preg n a n cy. C l i n Chest Med 32(1 ) : 1 , 201 1 .)
'
,
,
,
'_.;
,;, . ,---- --- - - -. - - ,�
. . -
. -
-
-
-
_ ••
Mate r n a l P hys i o l ogy
6
6
Pregnant
(7-9 mos . )
Not
pregnant
5
---�+ 5
4
4
FVC
�
:
3 3
FVC
:
)
TLC
2
2
FAC
RV
RV
o �--�--�-------------------�--�--� o
FIGURE 4-1 2 C h a n ges i n l u ng vol u mes with preg n a ncy. The most sig n ificant cha nges a re red uction i n fu nctional residual ca pacity ( F RC)
a nd its s u bcom ponents, expi ratory reserve vol u me (ERV) and res i d u a l vol u m e (RV), as wel l as i ncreases i n i n s p i ratory capacity (IC) a nd tidal
vol u me (). (Red rawn from Heg ewa ld MJ, Crapo RO: Respiratory physiology i n preg nancy. Clin Chest Med 3 2 ( 1 ) : 1 , 20 1 1 .)
of nasal congestion or total nasal resistance did not signiicantly
difer among trimesters or compared with nonpregnant controls.
• Oxygen Delivery
he amount of oxygen delivered into the lungs by the increased
tidal volume clearly exceeds oxygen requirements imposed by
pregnancy. Moreover, the total hemoglobin mass and, in turn,
total oxygen-carrying capacity rise appreciably during normal
pregnancy, as does cardiac output. Consequently, the mater­
nal arteriovenous oxygen diference is diminished. Oxygen con­
sumption grows approximately 20 percent during pregnancy,
and it is approximately 1 0 percent higher in multifetal gesta­
tions (Ajjimaporn, 20 1 4) . D uring labor, oxygen consumption
increases 40 to 60 percent (Bobrowski, 20 1 0) .
• Acid-Base Equilibrium
A greater awareness of a desire to breathe is common even early
in pregnancy (Milne, 1 978) . his may be interpreted as dyspnea,
which may suggest pulmonary or cardiac abnormalities when
none exist. This physiological dyspnea, which should not interfere
with normal physical activity, is thought to result from greater
tidal volume that lowers the blood Peo2 slightly and paradoxically
causes dyspnea. he increased respiratory efort during pregnancy,
and in turn the reduction in the partial pressure of carbon dioxide
in blood (Peo2) , is likely induced in large part by progesterone
and to a lesser degree by estrogen. Progesterone acts centrally,
where it lowers the threshold and raises the sensitivity of the che­
moreflex response to carbon dioxide (C02) 0ensen, 2005) .
To compensate for the resulting respiratory alkalosis, plasma
bicarbonate levels normally drop from 26 to 22 mmollL.
Although blood pH is increased only minimally, it does shift
the oxygen dissociation curve to the left. his shift increases the
ainity of maternal hemoglobin for oxygen-the Bohr fect­
thereby lowering the oxygen-releasing capacity of maternal
blood. This is ofset because the slight pH rise also stimulates
an increase in 2,3-diphosphoglycerate in maternal erythrocytes.
This shifts the curve back to the right (Tsai, 1 982) . hus,
reduced Peo2 from maternal hyperventilation aids CO 2 (waste)
transfer from the fetus to the mother while also aiding oxygen
release to the fetus .
URINARY SYSTEM
• Kidney
he urinary system undergoes several remarkable changes
in pregnancy (Table 4-5 ) . Kidney size grows approximately
1 .0 cm (Cietak, 1 985) . Both the glomerulariltration rate (CPR)
and renal plasma low increase early in pregnancy. he GFR
rises as much as 25 percent by the second week after concep­
tion and 50 percent by the beginning of the second trimester.
his hyperiltration results from two principal factors. First,
hypervolemia-induced hemodilution lowers the protein con­
centration and oncotic pressure of plasma entering the glomer­
ular microcirculation. Second, renal plasma flow increases by
approximately 80 percent before the end of the irst trimester
(Conrad, 20 1 4b; Odutayo, 20 1 2) . As shown in Figure 4- 1 3 ,
50
)
)
c
�
.
)
,
S
�
25
c
)
)
..
O �_--�--�--�-.�-��
o
1 -20
2 1 -30 3 1 -40
Weeks gestation
2
6-8
Weeks postpartum
FIGURE 4-1 3 Percentage i ncrement in g lomeru l a r fi ltration rate
(G FR) and rena l plasma flow (RPF) across gestation a n d in the puer­
peri u m . (Data from Od utayo, 20 1 2.)
65
66
Mate r n a l Anatomy a n d Physio l ogy
TABLE 4-5. Ren a l Cha nges in Normal P reg n a ncy
Parameter
Alteration
Clinical Relevance
Ki d n ey size
D i latation
Approxi mately 1 c m l o n g e r o n ra d iogra p h
Resembles hyd ro n e p h rosis o n sonog ra m o r
I V P (more ma rked o n r i g ht)
Re n a l fu n ct i o n
Glomeru la r fi ltrati o n rate a nd ren a l plasma
fl ow i ncrease 5 0%
Size ret u rn s to normal postpa rtu m
Ca n be co nfu sed with obstructive u ro pathy; reta i ned
u ri n e leads to col lecti o n e rrors; ren a l i nfections a re
m o re v i ru l ent; may be respon s i b l e for "d istention
synd ro me"; e lective pyelog ra p hy s h o u l d be deferred
to at l east 1 2 weeks postpa rt u m
Seru m creat i n i n e decreases d u ri ng n o rma l gestation;
> 0.8 m g/d L ( > 72 �mo l/L) creati n i n e a l ready
borderl i ne; p rote i n , a m i no acid, and g l u cose excretion
all i n c rease
Seru m bicarbo nate decreased by 4-5 m Eq/L; Pc02
decrea sed 1 0 mm Hg; a Pc02 of 40 mm Hg al ready
rep resents CO2 retention
Seru m os molal ity decrea ses 1 0 mOs m/L (se r u m Na
5 m Eq/L) d u ri n g normal gestation; i ncreased
placental meta bol i s m of AVP may cause tra nsient
d i a betes i n s i p i d u s d u ri n g p reg n a n cy
...
Ma i nte n a n ce of
aci d-base
Plasma os m o la l ity
Decreased bica rbonate t h reshold;
progestero ne sti m u lates respi ratory
center
Os m or eg u lation a lte red ; osmotic th resholds
for AVP rel ease and t h i rst d ecrease;
hormo n a l d is posa l rates i n c rease
...
AVP = va sopressi n; IVP = i ntravenous pye log ra p hy; Pc02= pa rt i a l p ress u re ca rbon d ioxide.
Mod ified fro m L i n d hei mer, 2000.
elevated GFR persists until term, even though renal plasma
flow declines during late pregnancy. Primarily as a consequence
of this elevated GFR, approximately 60 percent of nulliparas
during the third trimester experience urinary frequency, and 80
percent experience nocturia (F rederice, 20 1 3) .
During the puerperium, a marked GFR persists during the
first postpartum day, principally from the reduced glomerular
capillary oncotic pressure. A reversal of the gestational hyper­
volemia and hemodilution, still evident on the first postpar­
tum day, eventuates by the second week postpartum (Odutayo,
20 1 2) .
Studies suggest that relaxin, discussed earlier (p. 52) ,
may mediate both increased GFR and renal blood flow dur­
ing pregnancy (Conrad, 20 1 4a; Helal, 20 1 2) . Relaxin boosts
renal nitric oxide production, which leads to renal vasodilation
and lowered renal aferent and eferent arteriolar resistance.
This augments renal blood flow and GFR (Bramham, 20 1 6) .
Relaxin may also increase vascular gelatinase activity during
pregnancy, which leads to renal vasodilation, glomerular hyper­
iltration, and reduced myogenic reactivity of small renal arter­
ies (Odutayo, 20 1 2) .
A s with blood pressure, maternal posture may considerably
inluence several aspects of renal function. Late in pregnancy,
the sodium excretion rate in the supine position averages less
than half that in the lateral recumbent position. The efects of
posture on GFR and renal plasma low vary.
One unusual feature of the pregnancy-induced changes in
renal excretion is the remarkably increased amounts of some
nutrients lost in the urine. Amino acids and water-soluble vita­
mins are excreted in much greater amounts (Shibata, 20 1 3) .
Renal Fu n ction Tests
Of renal function tests, serum creatinine levels decline during
normal pregnancy from a mean of 0.7 to 0 . 5 mg/dL. Values of
0.9 mg/dL or reater sugest underying renal disease and prompt
further evaluation. Creatinine clearance in pregnancy averages
30 percent higher than the 1 00 to 1 1 5 mLi min in nonpregnant
women. his is a useful test to estimate renal function, provided
that complete urine collection is made during an accurately
timed period. If this is not done precisely, results are misleading
(Lindheimer, 2000, 20 1 0) . During the day, pregnant women
tend to accumulate water as dependent edema, and at night,
while recumbent, they mobilize this fluid with diuresis. This
reversal of the usual nonpregnant diurnal pattern of urinary flow
causes nocturia, and urine is more dilute than in nonpregnant
women. Failure of a pregnant woman to excrete concentrated
urine after withholding fluids for approximately 1 8 hours does
not necessarily signiy renal damage. In fact, the kidneys in these
circumstances function perfectly normally by excreting mobi­
lized extracellular fluid of relatively low osmolality.
U r i na lysis
Glucosuria during pregnancy may not be abnormal. The appre­
ciably increased GFR, together with impaired tubular reab­
sorptive capacity for filtered glucose, accounts for most cases
of glucosuria. Chesley ( 1 963) calculated that about a sixth
of pregnant women will spill glucose in the urine. hat said,
although common during pregnancy, when glucosuria is iden­
tiied, a search for diabetes mellitus is pursued.
Hematuria frequently results from contamination during
collection. If not, it most often suggests urinary tract disease
or infection. Hematuria is common after diicult labor and
delivery because of trauma to the bladder and urethra.
Proteinuria is typically deined in nonpregnant subjects as
a protein excretion rate of more than 1 50 mg/ d. Because of
the aforementioned hyperiltration and possible reduction of
tubular reabsorption, proteinuria during pregnancy is usu­
ally considered signiicant once a protein excretion threshold
Matern a l Phys i o l ogy
•
6
300
•
...
=
S
­
J
, 200
1 st Trimester
2nd Trimester
3rd Trimester
6
6
6
6
6
•
••
•
•
�_-l�--'
-r•
95 %
avoided. Disadvantageously, the amount of protein per unit of
creatinine excreted during a 24-hour period is not constant,
and the thresholds to deine abnormal vary. Nomograms for
urinary microalbumin and creatinine ratios during uncompli­
cated pregnancies have been developed (Waugh, 2003) .
• Ureters
·w
5
t 1 00
c
o
o
10
20
30
Gestational age (weeks)
40
FIGURE 4-1 4 Scatter p l ot of wo m e n s h owi n g 24- h o u r u ri n a ry
tot a l p rote i n excretion by gestatio n a l age. Mean a n d 95-percent
confidence l i m its a re o u t l i ned. (Red rawn from H i g by K, Su iter C R,
P h e l p s JY, et a l : N o r m a l va l u es of u r i n a ry a l bu m i n a n d tota l
p rote i n excret i o n d u ri n g p reg n a n cy. Am J Obstet Gynecol
1 7 1 :984, 1 994.)
of at least 300 mg/d is reached (Odutayo, 20 1 2) . Higby and
coworkers ( 1 994) measured protein excretion in 270 normal
women throughout pregnancy (Fig. 4- 1 4) . Mean 24-hour
excretion for all three trimesters was 1 1 5 mg, and the upper
9 5-percent conidence limit was 260 mg/d without significant
diferences by trimester. They showed that albumin excretion is
minimal and ranges from 5 to 30 mg/d. Proteinuria increases
with gestational age, which corresponds with the peak in CFR
(see Fig. 4- 1 3) (Odutayo, 20 1 2) .
After the uterus completely rises out of the pelvis, it rests on the
ureters. This laterally displaces and compresses them at the pel­
vic brim. Above this level, elevated intraureteral tonus results,
and ureteral dilatation is impressive (Rubi, 1 968) . It is right
sided in 86 percent of women (Fig. 4- 1 5) (Schulman, 1 975).
This unequal dilatation may result from cushioning provided
the left ureter by the sigmoid colon and perhaps from greater
right ureteral compression exerted by the dextrorotated uterus.
The right ovarian vein complex, which is remarkably dilated
during pregnancy, lies obliquely over the right ureter and may
also contribute to right ureteral dilatation.
Progesterone likely has some additional efect. Van Wagenen
and Jenkins ( 1 939) described continued ureteral dilatation
after removal of the monkey fetus but with the placenta left
in situ. The relatively abrupt onset of dilatation in women at
midpregnancy, however, seems more consistent with ureteral
compression.
Ureteral elongation accompanies distention, and the ureter
is frequently thrown into curves of varying size, the smaller
of which may be sharply angulated. hese so-called kinks are
Measuring U rine Protein. The three most commonly employed
approaches for assessing proteinuria are the qualitative classic
dipstick, the quantitative 24-hour collection, and the albumin/
creatinine or protein/creatinine ratio of a single voided urine
specimen. he pitfalls of each approach have been reviewed by
Conrad (20 1 4b) and Bramham (20 1 6) and their colleagues.
he principal problem with dipstick assessment is that it fails
to account for renal concentration or dilution of urine. For
example, with polyuria and extremely dilute urine, a negative
or trace dipstick could actually be associated with excessive pro­
tein excretion.
he 24-hour urine collection is afected by urinaty tract
dilatation, which is discussed in the next section. he dilated
tract may lead to errors related both to retention-hundreds
of milliliters of urine remaining in the dilated tract-and to
timing-the remaining urine may have formed hours before
the collection. To minimize these pitfalls, the patient is irst
hydrated and positioned in lateral recumbency-the deinitive
nonobstructive posture-for 45 to 60 minutes. After this, she
is asked to void, and this specimen is discarded. Immediately
following this void, her 24-hour collection begins. During the
final hour of collection, the patient is again placed in the lat­
eral recumbent position. But, at the end of this hour, the inal
collected urine is incorporated into the total collected volume
(Lindheimer, 20 1 0) .
Last, the protein/creatinine ratio i s a promising approach
because data can be obtained quickly and collection errors are
FIGURE 4-1 5 Hyd ronephrosis. P l a i n fi lm from the 1 5- m i n ute
image of a n i ntravenous pyelog ra m (IVP). Moderate hyd rone­
p h rosis on the rig ht (arrows) a n d m i l d hyd ronephrosis on the l eft
(arrowheads) a re both norma l for this 35-week gestation.
67
68
Maternal Anato m y a n d P hysiol ogy
poorly named, because the term connotes obstruction. hey are
usually single or double curves that, when viewed in a radio­
graph taken in the same plane as the curve, may appear as acute
angulations. Another exposure at right angles nearly always
identiies them to be gentle curves. Despite these anatomical
changes, complication rates associated with ureteroscopy in
pregnant and nonpregnant patients do not difer signiicantly
(Semins, 20 1 4) .
• Bladder
he bladder shows few significant anatomical changes before 1 2
weeks' gestation. Subsequently, however, increased uterine size,
the hyperemia that afects all pelvic organs, and hyperplasia of
bladder muscle and connective tissues elevate the trigone and
thicken its intraureteric margin. Continuation of this process to
term produces marked deepening and widening of the trigone.
The bladder mucosa is unchanged other than an increase in the
size and tortuosity of its blood vessels.
Bladder pressure in primigravidas increases from 8 cm H20
early in pregnancy to 20 cm H20 at term (Iosif, 1 980) . To
compensate for reduced bladder capacity, absolute and func­
tional urethral lengths increased by 6.7 and 4.8 mm, respec­
tively. Concurrently, maximal intraurethral pressure rises from
70 to 93 cm H20, and thus continence is maintained. Still, at
least half of women experience some degree of urinary incon­
tinence by the third trimester (Abdullah, 20 1 6a) . Indeed, this
is always considered in the diferential diagnosis of ruptured
membranes. Near term-particularly in nulliparas, in whom
the presenting part often engages before labor-the entire base
of the bladder is pushed ventral and cephalad. his converts the
normally convex surface into a concavity. As a result, diicul­
ties in diagnostic and therapeutic procedures are greatly accen­
tuated. Moreover, pressure from the presenting part impairs
blood and lymph drainage from the bladder base, often render­
ing the area edematous, easily traumatized, and possibly more
susceptible to infection.
GASTROI NTESTINAL TRACT
As pregnancy progresses, the stomach and intestines are dis­
placed cephalad by the enlarging uterus. Consequently, the
physical findings in certain diseases are altered. he appendix,
for instance, is usually displaced upward and somewhat later­
ally. At times, it may reach the right lank.
Pyrosis (heartburn) is common during pregnancy and is most
likely caused by reflux of acidic secretions into the lower esoph­
agus. Although the altered stomach position probably contrib­
utes to its frequency, lower esophageal sphincter tone also is
decreased. In addition, intraesophageal pressures are lower and
intragastric pressures higher in pregnant women. Concurrently,
esophageal peristalsis has lower wave speed and lower ampli­
tude (Ulmsten, 1 978) .
Gastric empying time is unchanged during each trimes­
ter and compared with nonpregnant women (Macfie, 1 99 1 ;
Wong, 2002, 2007) . During labor, however, and especially
after administration of analgesics, gastric emptying time may
be appreciably prolonged. As a result, one danger of general
anesthesia for delivery is regurgitation and aspiration of either
food-laden or highly acidic gastric contents.
Hemorrhoids are common during pregnancy (Shin, 20 1 5) .
hey are caused i n large measure b y constipation and elevated
pressure in rectal veins below the level of the enlarged uterus.
• Liver
Liver size does not enlarge during human pregnancy. Hepatic
arterial and portal venous blood flow, however, increase sub­
stantively (Clapp, 2000) .
Some laboratory test results of hepatic function are altered
in normal pregnancy (Appendix, p. 1 257) . Total alkaline phos­
phatase activity almost doubles, but much of the rise is attrib­
utable to heat-stable placental alkaline phosphatase isozymes.
Serum aspartate transaminase (AST) , alanine transaminase
(ALT) , 1-glutamyl transpeptidase (GGT) , and bilirubin levels
are slightly lower compared with nonpregnant values (Cat­
tozzo, 20 1 3 ; Ruiz-Extremera, 2005) .
The serum albumin concentration declines during preg­
nancy. By late pregnancy, albumin levels may be near 3.0 g/dL
compared with approximately 4.3 g/dL in nonpregnant women
(Mendenhall, 1 970) . Total body albumin levels rise, however,
because of pregnancy-associated increased plasma volume.
Serum globulin levels are also slightly higher.
Leucine aminopeptidase is a proteolytic liver enzyme whose
serum levels may be increased with liver disease. Its activity
is markedly elevated in pregnant women. he rise, however,
results from a pregnancy-speciic enzyme(s) with distinct
substrate speciicities (Song, 1 968). Pregnancy-induced ami­
nopeptidase has oxytocinase and vasopressinase activity that
occasionally causes transient diabetes insipidus.
• Gallbladder
During normal pregnancy, gallbladder contractility is reduced
and leads to greater residual volume (Braverman, 1 980) .
Progesterone potentially impairs gallbladder contraction by
inhibiting cholecystokinin-mediated smooth muscle stimula­
tion, which is the primary regulator of gallbladder contrac­
tion. Impaired emptying, subsequent stasis, and the increased
cholesterol saturation of bile in pregnancy contribute to the
increased prevalence of cholesterol gallstones in multiparas. In
one study, approximately 8 percent of women had gallbladder
sludge or stones when imaged at 1 8 and/or 36 weeks' gestation
(Ko, 20 1 4) .
h e pregnancy efects o n maternal serum bile acid concen­
trations are still incompletely characterized. his is despite the
long-acknowledged propensity for pregnancy to cause intrahe­
patic cholestasis and pruritus gravidarum from retained bile salts.
Cholestasis of pregnancy is described in Chapter 55 (p. 1 059) .
EN DOCRI NE SYSTEM
• Pituitary Gland
During normal pregnancy, the pUUltary gland enlarges by
approximately 1 35 percent (Gonzalez, 1 988) . This increase may
suiciently compress the optic chiasma to reduce visual fields.
Maternal Phys i o logy
Impaired vision from this is rare and usually due to macro ad­
enomas (Lee, 20 1 4) . Pituitary enlargement is primarily caused
by estrogen-stimulated hypertrophy and hyperplasia of the
lactotrophs (Feldt-Rasmussen, 20 1 1 ) . And, as discussed subse­
quently, maternal serum prolactin levels parallel the increasing
size. Gonadotrophs decline in number, and corticotrophs and
thyrotrophs remain constant. Somatotrophs are generally sup­
pressed due to negative feedback by the placental production
of growth hormone.
Peak pituitary size may reach 1 2 mm in MR images in the
irst days postpartum. he gland then involutes rapidly and
reaches normal size by 6 months postpartum (Feldt-Rasmus­
sen, 20 1 1 ) . he incidence of pituitary prolactinomas is not
increased during pregnancy (Scheithauer, 1 990) . When these
tumors are large before pregnancy-a macroadenoma measur­
ing : 1 0 mm-then growth during pregnancy is more likely
(Chap. 58, p. 1 1 32) .
he maternal pituitary gland is not essential for pregnancy
maintenance. Many women have undergone hypophysectomy,
completed pregnancy successfully, and entered spontaneous
labor while receiving compensatory glucocorticoids, thyroid
hormone, and vasopressin.
G rowth Hormone
During the first trimester, growth hormone is secreted predom­
inantly from the maternal pituitary gland, and concentrations
in serum and amnionic luid lie within the nonpregnant range
of 0 . 5 to 7 . 5 ng/mL (Kletzky, 1 985). As early as 6 weeks' ges­
tation, growth hormone secreted from the placenta becomes
detectable, and by approximately 20 weeks, the placenta is the
principal source of growth hormone secretion (Perez-Ibave,
20 1 4) . Maternal serum values rise slowly from approximately
3.5 ng/mL at 1 0 weeks to plateau at about 1 4 ng/mL after
28 weeks. Growth hormone in amnionic fluid peaks at 1 4 to
1 5 weeks and slowly declines thereafter to reach baseline values
after 36 weeks.
Placental growth hormone-which difers from pituitary
growth hormone by 1 3 amino acid residues-is secreted
by syncytiotrophoblast in a nonpulsatile fashion (Newbern,
20 1 1 ) . Its regulation and physiological efects are incompletely
understood, but it inluences fetal growth via up regulation of
insulin-like growth factor 1 (IGF- 1 ) . Higher levels have been
linked with development of preeclampsia (MinaI, 2007; Perez­
Ibave, 20 1 4) . Further, placental expression correlates positively
with birthweight but negatively with fetal-growth restriction
(Koutsaki, 20 1 l ) . Maternal serum levels are associated with
uterine artery resistance changes (Schiessl, 2007) . hat said,
fetal growth still progresses in the complete absence of this
hormone. Although not absolutely essential, the hormone may
act in concert with placental lactogen to regulate fetal growth
(Newbern, 20 1 1 ) .
Prolactin
Maternal plasma prolactin levels increase markedly during nor­
mal pregnancy. Concentrations are usually tenfold greater at
term-about 1 50 ng/mL-compared with those of nonpreg­
nant women. Paradoxically, plasma concentrations drop after
delivery even in women who are breastfeeding. During early
lactation, pulsatile bursts of prolactin secretion are a response
to suckling.
The principal function of maternal prolactin is to ensure lac­
tation. Early in pregnancy, prolactin acts to initiate DNA syn­
thesis and mitosis of glandular epithelial cells and presecretory
alveolar cells of the breast. Prolactin also augments the number
of estrogen and prolactin receptors in these cells. Finally, pro­
lactin promotes mammary alveolar cell RNA synthesis, galac­
topoiesis, and production of casein, lactalbumin, lactose, and
lipids (Andersen, 1 982) . A woman with isolated prolactin dei­
ciency failed to lactate after two pregnancies (Kauppila, 1 987) .
This establishes prolactin as a requisite for lactation but not for
pregnancy. Grattan (20 1 5) has reviewed the numerous physi­
ological roles of prolactin for facilitating maternal adaptations
to pregnancy. A possible role is proposed for a prolactin frag­
ment in the genesis of peripartum cardiomyopathy (Chap. 49,
p. 963) (Cunningham, 20 1 2) .
Prolactin is present i n amnionic fluid i n high concen­
trations. Levels of up to 1 0,000 ng/mL are found at 20 to
26 weeks' gestation. Thereafter, levels decline and reach a nadir
after 34 weeks. Uterine decidua is the synthesis site of prolactin
found in amnionic luid. Although the exact function of amni­
onic luid prolactin is unknown, impaired water transfer from
the fetus into the maternal compartment to thereby prevent
fetal dehydration is one suggestion.
Oxytoci n a n d Antid i u retic Hormone
These two hormones are secreted from the posterior pituitary
gland. The roles of oxytocin in parturition and lactation are
discussed in Chapters 2 1 (p. 4 1 6) and 36 (p. 657) , respec­
tively. Brown and colleagues (20 1 3) have reviewed the com­
plex mechanisms that promote quiescence of oxytocin systems
during pregnancy. Levels of antidiuretic hormone, also called
vasopressin, do not change during pregnancy.
• Thyroid Gland
hyrotropin-releasing hormone (TRH) is secreted by the hypo­
thalamus and stimulates thyrotrope cells of the anterior pitu­
itary to release thyroid-stimulating hormone (TSH), also called
thyrotropin. TRH levels do not rise during normal pregnancy.
However, TRH does cross the placenta and may serve to stimu­
late the fetal pituitary to secrete TSH (horpe-Beeston, 1 99 1 ) .
Serum TSH and hCG levels vary with gestational age
(Fig. 4- 1 6) . As discussed in Chapter 5 (p. 98), the a-subunits
of the two glycoproteins are identical, whereas the 3-subunits,
although similar, difer in their amino acid sequence. As a result
of this structural similarity, hCG has intrinsic thyrotropic activ­
ity, and thus, high serum hCG levels cause thyroid stimulation.
Indeed, TSH levels in the irst trimester decline in more than
80 percent of pregnant women, however, they still remain in
the normal range for nonpregnant women
The thyroid gland boosts production of thyroid hormones
by 40 to 1 00 percent to meet maternal and fetal needs (Moleti,
20 1 4) . To accomplish this, the thyroid gland undergoes moder­
ate enlargement during pregnancy caused by glandular hyper­
plasia and greater vascularity. Mean thyroid volume increases
from 12 mL in the first trimester to 1 5 mL at term (Glinoer,
69
70
Mate r n a l A natomy a nd Physiology
and triiodothyronine (T3) concentrations, but do not afect the
physiologically important serum ree T4 and ree T3 levels. Spe­
cifically, total serum T4 levels rise sharply beginning between 6
and 9 weeks' gestation and reach a plateau at 1 8 weeks. Serum
free T4 levels rise only slightly and peak along with hCG levels,
and then they return to normal.
Interestingly, T4 and T3 secretion is not similar for all preg­
nant women (G linoer, 1 990) . Approximately a third of women
experience relative hypothyroxinemia, preferential T3 secretion,
and higher, albeit normal, serum TSH levels. hus, thyroidal
adjustments during normal pregnancy may vary considerably.
The fetus relies on maternal T4, which crosses the placenta
in small quantities to maintain normal fetal thyroid function
(Chap. 58, p. 1 1 1 8) . Recall that the fetal thyroid does not begin
to concentrate iodine until 1 0 to 1 2 weeks' gestation. he syn­
thesis and secretion of thyroid hormone by fetal pituitary TSH
ensues at approximately 20 weeks. At birth, approximately 30
percent of the T4 in umbilical cord blood is of maternal origin
(Leung, 20 1 2) .
Mother
TBG
Total T4
Thyrotropin
Fetus
Thyroid Fu nction Tests
10
20
Week of pregnancy
30
40
FIGURE 4- 1 6 Relative cha nges i n maternal a nd fetal thyroid fu n c­
tion across preg na ncy. Maternal changes i ncl ude a ma rked a n d
early i n c rease i n hepatic prod uction o f thyroxine- b i n d i n g g l o b u l i n
(TBG) a nd placenta l prod uction o f h u m a n chorion ic g o nadotropin
(hCG). I nc reased TBG i ncreases serum thyroxine (T4) concentrations.
hCG h a s thyrotropi n-l i ke activity a nd sti m u lates maternal free T4
secretion. Th i s tra n sient hCG-i n d uced increase i n ser u m T4 levels
i n h i bits maternal secretion of thyrotropin. Except for m i n i ma l ly
increased free T4 levels when hCG pea ks, these levels a re essentia l ly
u ncha nged. Feta l levels of a l l serum thyroid a n a lytes i nc rease incre­
menta l ly across preg n a n cy. Fetal triiodothyro n i n e (T3) does not
i nc rease u ntil late preg n a n cy. (Mod ified from Bu rrow, 1 994.)
Normal suppression of TSH during pregnancy may lead to a
misdiagnosis of subclinical hyperthyroidism. Of greater concern
is the potential failure to identiy women with early hypothy­
roidism because of suppressed TSH concentrations. To miti­
gate the likelihood of such misdiagnoses, Dashe and coworkers
(2005) conducted a population-based study at Parkland Hos­
pital to develop gestational-age-specific TSH normal curves
for both singleton and twin pregnancies (Fig. 4- 1 7) . Similarly,
Ashoor and associates (20 1 0) established normal ranges for
maternal TSH , free T4, and free T3 at 1 1 to 1 3 weeks' gestation.
hese complex alterations of thyroid regulation do not
appear to alter maternal thyroid status as measured by meta­
bolic studies. lthough basal metabolic rate increases progres­
sively by as much as 25 percent during normal pregnancy, most
6
5
; 4
s
4.0
-
�
:
n
�
3
2
50th
0.4
0
0
1 990) . That said, normal pregnancy does not typically cause sig­
nificant thyromegaly, and thus any goiter warrants evaluation.
Early in the first trimester, levels of the principal carrier
protein-thyroid-binding globulin (TBG)-rise, reach their
zenith at about 20 weeks, and stabilize at approximately double
baseline values for the remainder of pregnancy (see Fig. 4- 1 6) .
h e greater TBG concentrations result from both higher hepatic
synthesis rates-due to estrogen stimulation-and lower metab­
olism rates due to greater TBG sialylation and glycosylation.
These elevated TBG levels increase total serum thyroxine (T4)
7
\
10
20
30
40
Gestational age (weeks)
FIGURE 4-1 7 Gestational age-specific thyroid-sti m u lating hor­
mone (TSH) nomogra m derived from 1 3,599 singleton preg nan­
cies. The non preg n a nt reference va l u es of 4.0 a n d 0.4 mUll a re
represented as solid black li nes. U pper shaded a rea represents the
28 percent of sing leton preg na ncies with TSH va l ues above the
97.5th percentile t h reshold that wou l d not have been identified as
a b norma l based on the assay reference va l u e of 4.0 m Ull. lower
shaded a rea represents sing leton preg n a n cies that would have
been (fa l sely) identified as having TSH s u p p ression based on the
assay reference va l ue of 0.4 m Ull. (Data from Dashe, 2005.)
Materna l Phys i o l ogy
of this greater oxygen consumption can be attributed to fetal
metabolic activity. If fetal body surface area is considered along
with that of the mother, the predicted and observed basal meta­
bolic rates are similar to those in nonpregnant women.
Iod i n e Statu s
Iodine requirements increase during normal pregnancy (Chap.
58, p. 1 1 27) . In women with low or marginal intake, deiciency
may manifest as low T4 and higher TSH levels. Importantly,
more than a third of the world population lives in areas where
iodine intake is marginal. For the fetus, early exposure to thy­
roid hormone is essential for the nervous system, and despite
public health programs to supplement iodine, severe iodine
deiciency resulting in cretinism afects more than 2 million
people globally (Syed, 20 1 5) .
• Parathyroid Glands
In one longitudinal investigation of 20 women, all markers
of bone turnover rose during normal pregnancy and failed to
reach baseline levels by 1 2 months postpartum (More, 2003).
Investigators concluded that the calcium needed for fetal
growth and lactation may be drawn at least in part from the
maternal skeleton. he factors afecting bone turnover yield a
net result favoring fetal skeletal formation at the expense of the
mother, such that pregnancy is a vulnerable period for osteo­
porosis (Sanz-Salvador, 20 1 5) . hat said, prevention is diicult
due to a paucity of identiiable risk factors.
Pa rathyroid Hormone
Acute or chronic declines in plasma calcium or acute drops in
magnesium levels stimulate parathyroid hormone (PTH) release.
Conversely, greater calcium and magnesium levels suppress PTH
levels. he action of this hormone on bone resorption, intestinal
absorption, and kidney reabsorption is to raise extracellular luid
calcium concentrations and lower phosphate levels.
Fetal skeleton mineralization requires approximately 30 g of
calcium, primarily during the third trimester (Sanz-Salvador,
20 1 5) . Although this amounts to only 3 percent of the total
calcium held within the maternal skeleton, the provision of cal­
cium still challenges the mother. In most circumstances, aug­
mented maternal calcium absorption provides the additional
calcium. During pregnancy, the amount of calcium absorbed
rises gradually and reaches approximately 400 mg/ d in the third
trimester. Greater calcium absorption appears to be mediated
by elevated maternal 1 ,25-dihydroxyvitamin D concentra­
tions. This occurs despite decreased PTH levels during early
pregnancy, which is the normal stimulus for active vitamin D
production within the kidney. Indeed, PTH plasma concentra­
tions decline during the irst trimester and then rise progres­
sively throughout the remainder of pregnancy (Pitkin, 1 979) .
he increased production of active vitamin D is likely due to
placental production of either PTH or a PTH-related protein
(PTH-rP) . Outside pregnancy and lactation, PTH-rP is usually
detectable only in serum of women with hypercalcemia due to
malignancy. During pregnancy, however, PTH-rP concentra­
tions increase signiicantly. his protein is synthesized in both
fetal tissues and maternal breasts.
Ca lcito n i n
h e C cells that secrete calcitonin are located predominantly in
the perifollicular areas of the thyroid gland. Calcitonin opposes
actions of PTH and vitamin D and protects the matenal skel­
eton during times of calcium stress. Pregnancy and lactation
cause profound maternal calcium stress, ostensibly for the sake
of the fetus. Indeed, fetal calcitonin levels are at least twofold
higher than maternal levels (Ohata, 20 1 6) . And although
maternal levels fall during pregnancy, they generally rise post­
partum (M011er, 20 1 3) .
Calcium and magnesium promote the biosynthesis and
secretion of calcitonin. Various gastric hormones-gastrin,
pentagastrin, glucagon, and pancreozymin-and food inges­
tion also increase calcitonin plasma levels.
• Adrenal Glands
Cortisol
In normal pregnancy, unlike their fetal counterparts, the mater­
nal adrenal glands undergo little, if any, morphological change.
The serum concentration of circulating cortisol rises, but much
of it is bound by transcortin, the cortisol-binding globulin. The
adrenal secretion rate of this principal glucocorticoid is not ele­
vated, and probably it is lower than in the nonpregnant state.
he metabolic clearance rate of cortisol, however, is dimin­
ished during pregnancy because its half-life is nearly doubled
compared with that for nonpregnant women (Migeon, 1 957) .
Administration of estrogen, including most oral contraceptives,
causes changes in serum cortisol levels and transcortin similar
to those of pregnancy Qung, 20 1 1 ) .
During early pregnancy, the levels o f circulating adrenocor­
ticotropic hormone (A CTH) , also known as corticotropin, are
dramatically reduced. As pregnancy progresses, ACTH and
free cortisol levels rise equally and strikingly (Fig. 4- 1 8) . This
500
400
300
T
200
40
80
60
,
S
50
I
0
«
50
30
70
J
E
j
20
40
30
10
20
10
0
10
20
30
40
Weeks' gestation
FIGURE 4- 1 8 Seria l increa ses in ser u m cortisol (blue line) a n d
adrenocorticotropic hormone (ACTH) (red line) across normal
preg n a n cy. (Data fro m Ca rr, 1 98 1 .)
I
71
72
Materna l Anatomy a n d Physiology
apparent paradox is not understood completely. Some suggest
that greater free cortisol levels in pregnancy result from a "reset­
ting" of the maternal feedback mechanism to higher thresh­
olds (Nolten, 1 98 1 ) . his might result from tissue reractoriness
to cortisol. Others assert that these incongruities stem from
an antagonistic action of progesterone on mineralocorticoids
(Keller-Wood, 200 1 ) . Thus, in response to elevated progester­
one levels during pregnancy, an elevated free cortisol is needed
to maintain homeostasis. Other theories include possible roles
for higher free cortisol in preparation for the stress of preg­
nancy, delivery, and lactation. This pattern might also influence
postpartum behavior and parenting roles (Conde, 20 1 4) .
Al dosterone
As early as 15 weeks' gestation, the maternal adrenal glands
secrete considerably increased amounts of aldosterone, the prin­
cipal mineralocorticoid. By the third trimester, approximately
1 mg/d is released. If sodium intake is restricted, aldosterone
secretion is even further elevated (Watanabe, 1 963) . Concur­
rently, levels of renin and angiotensin II substrate normally rise,
especially during the latter half of pregnancy. his scenario pro­
motes greater plasma levels of angiotensin II, which acts on the
zona glomerulosa of the maternal adrenal glands and accounts
for the markedly elevated aldosterone secretion. Some suggest
the increased aldosterone secretion during normal pregnancy
afords protection against the natriuretic efect of progesterone
and atrial natriuretic peptide. Gennari-Moser and colleagues
(20 1 1 ) provide evidence that aldosterone, as well as cortisol,
may modulate trophoblast growth and placental size.
Deoxyco rticostero n e
Maternal plasma levels o f this potent mineralocorticosteroid
progressively increase during pregnancy. Indeed, plasma lev­
els of deoxycorticosterone rise to near 1 500 pg/mL by term, a
more than 1 5-fold increase (Parker, 1 980) . his marked eleva­
tion does not derive from adrenal secretion but instead rep­
resents augmented kidney production resulting from estrogen
stimulation. The levels of deoxycorticosterone and its sulfate
in fetal blood are appreciably higher than those in maternal
blood, which suggests transfer of fetal deoxycorticosterone into
the maternal compartment.
Androgens
In balance, androgenic aCtiVlty rises during pregnancy, and
both maternal plasma levels of androstenedione and testosterone
are increased. This inding is not totally explained by alterations
in their metabolic clearance. Both androgens are converted to
estradiol in the placenta, which increases their clearance rates.
Conversely, greater plasma sex hormone-binding globulin lev­
els in gravidas retard testosterone clearance. Thus, the produc­
tion rates of maternal testosterone and androstenedione during
human pregnancy are increased. he source of this higher
C19-steroid production is unknown, but it likely originates in
the ovary. Interestingly, little or no testosterone in maternal
plasma enters the fetal circulation as testosterone. Even when
massive testosterone levels are found in the circulation of preg­
nant women, as with androgen-secreting tumors, testosterone
concentrations in umbilical cord blood are likely to be unde­
tectable. his results from the near complete trophoblastic con­
version of testosterone to 1 73-estradiol.
Maternal serum and urine levels of dehydroepiandrosterone
suate are lower during normal pregnancy. his stems from a
greater metabolic clearance through extensive maternal hepatic
1 6.-hydroxylation and placental conversion to estrogen
(Chap. 5, p. 1 03).
MUSCULOSKELETAL SYSTEM
Progressive lordosis is a characteristic feature of normal preg­
nancy. Compensating for the anterior position of the enlarging
uterus, lordosis shifts the center of gravity back over the lower
extremities. The sacroiliac, sacrococcygeal, and pubic joints have
increased mobility during pregnancy. However, as discussed ear­
lier (p. 52) , increased joint laxity and associated discomfort dur­
ing pregnancy do not correlate with increased maternal serum
levels of estradiol, progesterone, or relaxin (Aldabe, 20 1 2; Mar­
nach, 2003; V0llestad, 20 1 2) . Most relaxation takes place in the
first half of pregnancy. It may contribute to maternal posture
alterations and in turn create lower back discomfort. s dis­
cussed in Chapter 36 (p. 66 1 ) , although some symphyseal sepa­
ration likely accompanies many deliveries, those greater than 1
cm may cause significant pain (Shnaekel, 20 1 5) .
Aching, numbness, and weakness also occasionally are
experienced in the upper extremities. his may result from
the marked lordosis and associated anterior neck flexion and
shoulder girdle slumping, which produce traction on the ulnar
and median nerves (Crisp, 1 964) . he latter may give rise to
symptoms mistaken for the carpal tunnel syndrome (Chap. 60,
p. 1 1 67) . Joint strengthening begins immediately following
delivery and is usually complete within 3 to 5 months. Pelvic
dimensions measured by MR imaging up to 3 months after
delivery are not significantly diferent from prep regnancy mea­
surements (Huerta-Enochian, 2006) .
CENTRAL N E RVOUS SYSTEM
• Memory
Central nervous system changes are relatively few and mostly
subtle. Women often report problems with attention, concen­
tration, and memory throughout pregnancy and the early puer­
perium. Systematic studies of memory in pregnancy, however,
are limited and often anecdotal. Keenan and associates ( 1 998)
longitudinally investigated memory in pregnant women and a
matched control group. hey found pregnancy-related memory
decline that was limited to the third trimester. his decline was
not attributable to depression, anxiety, sleep deprivation, or
other physical changes associated with pregnancy. It was tran­
sient and quickly resolved following delivery. Others have found
poorer verbal recall and processing speed and worse spatial rec­
ognition memory in pregnancy (Farrar, 20 1 4; Henry, 20 1 2) .
Zeeman and coworkers (2003) used MR imaging t o measure
cerebral blood low across pregnancy. They found that mean
blood flow in the middle and posterior cerebral arteries declined
progressively from 1 47 and 56 mLimin when nonpregnant to
Matern a l Phys i o logy
1 1 8 and 44 mLlmin late in pregnancy, respectively. Mecha­
nisms and signiicance of the decline are unknown. Pregnancy
does not . afect cerebrovascular autoregulation (Bergersen,
2006; Cipolla, 20 1 4) .
• Eyes
Intraocular pressure drops during pregnancy and is attrib­
uted partly to greater vitreous outlow. Corneal sensitivity is
decreased, and the greatest changes are late in gestation. Most
pregnant women demonstrate a measurable but slight increase
in corneal thickness, thought to be due to edema. Conse­
quently, they may have diiculty with previously comfortable
contact lenses. Brownish-red opacities on the posterior sur­
face of the cornea-Krukenberg spindles-are observed with a
higher than expected frequency during pregnancy. Hormonal
efects similar to those observed for skin lesions are believed to
cause this increased pigmentation. Other than transient loss of
accommodation reported with both pregnancy and lactation,
visual function is unafected by pregnancy. These changes dur­
ing pregnancy and pathological eye aberrations were reviewed
by Grant and Chung (20 1 3) .
• Sleep
Beginning as early as 1 2 weeks' gestation and extending through
the first 2 months postpartum, women have diiculty with
falling asleep, frequent awakenings, fewer hours of night sleep,
and reduced sleep eiciency (Pavlova, 20 1 1 ) . Abdullah and col­
leagues (20 1 6b) concluded that sleep apnea is more common in
pregnancy, especially in obese patients. he greatest disruption
of sleep is encountered postpartum and may contribute to post­
partum blues or to frank depression a uulia Paavonen, 20 1 7) .
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;
=
�
80
C H A PT E R 5
I m pl a ntation a nd Placenta l
Development
. . . . . 80
OVARIAN-ENDOMETRIAL CYCLE .
. . . . . 85
DECIDUA.
IMPLANTATION AND EARLY TROPHOBLAST
FORMATION . . . . . . . . . . . . . . .
PLACENTA AND CHORION .
UMBILICAL CORD. . . . . . . . . . . . . . . . . . .
.
All obstetricians should understand the basic biological steps
required for women to successully achieve pregnancy. Several
. . . . . 87
abnormalities can fect each of these and lead to infertili' or
. 90
tion continues during almost 40 years between menarche and
. . . . . 95
AMNION .
strides have followed to uncover the steps of implantation and
placental structure and function.
pregnancy loss. In most women, spontaneous, cyclical ovula­
menopause. Without contraception, there are approximately
400 opportunities for pregnancy, namely, the day of ovulation
. . . . . . . . . . 97
and its few preceding days. his narrow window for fertiliza­
. 98
steroids. Moreover, these hormones promote optimal endome­
PLACENTAL HORMONES.
FETAL ADRENAL GLAND-PLACENTAL
INTERACTIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . .
tion is controlled by tightly regulated production of ovarian
trial regeneration after menstruation in preparation for the next
. . . . 104
implantation window.
If fertilization occurs, events thac begin ater blastocyst
implantation persist until parturition. hese derive from a
unique interaction between fetal trophoblasts and the maternal
endometrium. which has been transformed into the
decidua.
The ability of a mother and her fetus to coexist as two distinct
immunological systems results from endocrine. paracrine. and
Almost immediately ater the impamltio1 of the ovum, its
trophoblast begins to prolerate and lJ1d, the s.rrounding
decidual tissue. As it does so, it breaks through the walls of
the moumal capilaries, from which the blood escapes and
orms cavities, which are boundedparty by trophobast and
party by decidua. ?he maternal blood spaces established in
this manner represent the earliest stages of the intervillous
blood spaces ofthe inure placenta.
-). Whitridge Williams ( 1 903)
immunological modiication of fetal and maternal tissues in a
manner not seen elsewhere. In addition. the placenta mediates
a unique fetal-maternal communication system. which creates
a hormonal environment that initially maintains pregnancy
and eventually initiates events leading to parturition.
OVARIAN-ENDOMETRIAL CYCLE
Predictable. regular. cyclical. and spontaneous ovulatory men­
strual cycles are regulated by complex interactions of the hypo­
1903, the histopathological and embryological descrip­
thalamic-pituitay-ovarian axis. Concurrently, cyclical changes
tions of ovum implanrarion and placental development had
in endometrial histology are faithfully reproduced ( Fig. ;- 1 ).
In
been extensively studied and described. However, the origins
Essentials players in this process include follicle-stimulating
and functions of pregnancy hormones were largely unknown.
hormone (FSH) and luteinizing hormone (LH), which are
Indeed, it was another 2 5 to 30 years before estrogen and pro­
pituitary-derived gonadotropins, and the ovarian sex steroid
gesterone were discovered. In the past 50 years, remarkable
hormones estrogen and progesterone.
Impla ntation and Placental Development
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Antral
Dominant
follicles
follicle
Ovulation
Corpus
luteum
(ell
Antral
Dominant
follicles
follicle
Fertilization &
implantation
..
'l
CL
.
�
CL of
pregnancy
�),
�
Menses
Menstrual cycle day
Embryonic age
.! ! ! ! ! ! ! ! ! ! ! ! ! . ! ! ! ! ! ! ! ! ! ! ! ! ! •!
14
Gestational age
20
FIGURE 5- 1 Gonadotropin control of the ovarian and endometrial cycles. The ovarian end ometri a l cycle has been structured as a 28-day
cycle. The follicular phase (days 1 to 14) is characterized by rising estrogen levels, endometrial t h i c ken ing and selection of the dominant
"ovulatory" follicle. During the luteal phase (days 14 to 21 I, the corpus luteum (ell p roduces estrogen and progesterone, which prepare the
endometrium for implantation. If implantation occurs, the developing blastocyst begins to produce human chorionic gonadotropin (hCG)
and rescues the corpus luteum, thus maintaining progesterone production. FSH follicle-stimulating hormon e; LH luteinizing hor m on e.
-
,
=
The average cycle duration approximates 28 days but ranges
from 25 to 32 days, even for a given woman. The follicular or
proliferative phase shows considerable phase-length variation.
This contrasts with the luteal or secretory POStovulatory phase
of the cycle, which is remarkably constant at 12 to 14 days.
• Ovarian Cycle
Follicular Phase
The human ovary contains 2 million oocytes at birth, and
approximately 400,000 follicles are present at puberty onset
(Baker, 1 963). These are depleted at a rate of approximately
1000 follicles per month until age 35, when this rate accelerates
(Faddy, 1992). Only 400 follicles are normally released during
female reproductive life. Therefore, more than 99.9 percent of
these undergo atresia through a process of cell death termed
apoptosis (Gougeon, 1996; Kaipia, 1 997).
=
Follicular development consists of several stages. Primordial
follicles undergo gonadotropin-independent recruitment from
the resting pool and then progress from primary and secondary
follicles to the antral stage. This appears to be controlled by
locally produced growth factors. Two members ofthe transform­
ing growth factor-3 family include growth diferentiation fac­
tor 9 (GDF9) and bone morphogenetic protein 1 5 (BMP- 1 5),
which regulate granulosa cell proliferation and diferentiation as
primary follicles grow (Trombly, 2009; Yan, 2001). hey also
stabilize and expand the cumulus oocyte complex in the ovi­
duct (Hreinsson, 2002). These factors are produced by oocytes,
suggesting that the early steps in follicular development are, in
part, oocyte controlled. As antral follicles develop, surrounding
stromal cells are recruited, by a yet-to-be-deined mechanism,
to become thecal cells.
Although not required for early follicular maturation, FSH
is required for further development of large antral follicles
81
82
Placentation, Embryogenesis, and Fetal Development
(Hillier,
2001).
Theca cell
a cohon, begins a phase of semisynchro­
IlOUS
growth based on their marurarion
stare during rhe FSH rise in rhe late luteal
phase of rhe previous cycle. This FSH
increase leading to further follicular devel­
opmenr is called the seection winow of
me ovarian cycle (Macklon, 200 1 ) . Only
follicles progressing to this stage develop
the capacity
[Q
L
�
� CAMP
_ _ _ _ _ _ _ _
C
;
Theca lutein cell
Cholesterol
•
!
Androstenedione
L
�
CAMP- - - - - - - - .
!
Androstenedione
C
�
' C i rculation
Cholesterol
r ' C',,""'.o
Basement membrane
produce estrogen.
During rhe follicular phase, estro­
gen levels rise in proportion to growth
of a dominant follicle
and
{Q
rhe
increase in its number of granulosa cells
(see Fig. 5 - 1 ) . These cells are rhe exclu­
sive site of FSH receptor expression.
lle elevation of Circulating FSH levels
during the late luteal phase of the previ­
ous cycle stimulates an increase in FSH
receptors and subsequently, the ability
of cytochrome P450 aromatase within
granulosa cells to conven androstenedi­
one into estradiol. The requirement fo r
thecal cells, which respond ro LH, and
granulosa cells, which respond to FSH,
represents the two-gonadotropin, two­
ceH hypothesis for estrogen biosynthesis
(Short, 1 962). As shown in F igure 5-2 ,
FSH
LUTEAL PHASE/PREGNANCY
FOLLICULAR PHASE
During each ovarian
cycle. a group of antral follicles, known as
induces aromatase and expan­
sion of the antrum of growing follicles.
The follicle within the cohorr that is
Estradiol_ Androstenedione
�
,,
,, ,
,
-:Androstenedione
,
Progesterone
LDL
cAMP
J
Estradiol
l
\,
.- - - - - - -
:\AMP
Cholesterol
G ra nu losa
cell
FSH
Granulosa-lutein cell
V
W
LH
FIGURE 5-2 The two-cell, two-gonadotropin principle of ovarian steroid hormone produc­
tion. During the follicular phase (left panen, l uteinizing hormone (LH) controls theca cell
production of androstenedione, which diffuses into the adjacent granulosa cells and acts as
precursor for estradiol biosynthesis. The granulosa cell capacity to convert androstenedione
to estradiol is controlled by follicle-stimulating hormone (FSH), After ovulation (right panen,
the corpus luteum forms and both theca-lutein and granulosa-lutein cells respond to LH.
The theca-lutein cells continue to produce androstenedione, whereas granulosa-lutein cells
greatly increase their capacity to produce progesterone and to convert androstenedione to
estradiol. LH and hCG bind to the same LH-hCG receptor. If pregnancy occurs (right pane�,
human chorionic gonadotropin (hCG) rescues the corpus luteum through their shared LH­
hCG receptor. Low-density lipoproteins (LOL) are an important source of cholesterol for
steroidogenesis, cAMP cyclic adenosine monophosphate.
=
most responsive to FSH is likely to
be the irst to produce estradiol and initiate expression of LH
precise predictor of ovulation. It occurs 34 to 36 hours before
receptors.
ovum release from the follicle (see Fig. 5 - 1 ) . LH secretion peaks
Mrer the appearance of LH receptors, the preovulatory
1 0 to 1 2 hours before ovulation and stimulatcs resumption of
granulosa cells begin to secrete small quantities of progesterone.
meiosis in the ovum and release of the irst polar body. Studies
The preovulatory progesterone secrecion, although somewhat
suggest that in response to LH, greater progesterone and pros­
limited, is believed to exert positive feedback on the estrogen­
taglandin production by the cumulus cells, as well as GDF9
primed pituitary to either calise or augment LH release. In addi­
and BMP- 1 5 by the oocyte, activates expression of genes criti­
tion, during the late follicular phase, LH stimulates thecal cell
production of androgens, particularly androstenedione, which
cal to formarion of a hyaluronan-rich extracellular matrix by
the cumulus complex (Richards, 2007). As seen in F igu n: ) - 3 ,
are then transferred to the adjacent follicles where they are aro­
during synthesis of this matrix, cumulus cells lose contact with
matized to esnadiol (see Fig. 5-2). During the early follicular
one another and move outward from the oocyte along the hyal­
phase, granulosa cells also produce in hibin 3, which can feed
uronan polymer-this process is called expansion. This results
back on the pituitary to inhibit FSH release (Groome, 1 996).
in a 20-fold augmentation of the cumulus complex volume and
As the dominant foHicle begins to grow, estradiol and inhibin
coincides with an LH-induced remodeling of the ovarian extra­
production rises and results in a decline of follicular-phase
cellular matrix. hese allow release of the mature oocyte and
FSH. This drop in FSH levels is responsible for the failure of
its surrounding cumulus cells through the surface epirhelium.
other follicles to reach preovulatory status-the Graaian fol­
Activation of proteases likely plays a pivotal role in weakening
licle stage-during any one cycle. Thus, 95 percent of plasma
the follicular basement membrane and ovulation (Curry, 2006;
estradiol produced at this time is secreted by the dominant
Ny, 2002).
follicle-thc one destined to ovulate. Concurrently, the con­
tralateral ovary is relatively inactive.
Ovulation
Luteal Phase
Following ovulation, rhe corpus luteum develops from the
remains of the Graaian follicle in a process referred to as
The onset of rhe gonadotropin surge resulting from increas­
luteiniation. The basement membrane separating the granu­
ing estrogen secretion by preovulatory follicles is a relatively
losa-lutein and theca-lutein cells breaks down, and by day 2
I m p l a ntation a n d P l ace nta l Deve l op m e nt
• Estrogen and Progesterone Action
FIGURE 5-3 An ovu lated c u m u l u s-oocyte co mpl ex. An oocyte is
at the center of the com plex. C u m u l u s cel l s a re widely sepa rated
from each other by the hya l u ro n a n-rich extracel l u l a r matrix. (Used
with permission from Dr. Kevin J . Doody.)
postovulation, blood vessels and capillaries invade the granulosa
cell layer. The rapid neo�ascularization of the once-avascular
granulosa may be due to angiogenic factors that include vas­
cular endothelial growth factor (VEG F) and others produced
by theca-lutein and granulosa-lutein cells in response to LH
(Albrecht, 2003; Fraser, 200 1 ) . D uring luteinization, these cells
undergo hypertrophy and increase their capacity to synthesize
hormones.
LH is the primary luteotropic factor responsible for corpus
luteum maintenance (Vande Wiele, 1 970) . Indeed, LH injec­
tions can extend the corpus luteum life span in normal women
by 2 weeks (Segalof, 1 9 5 1 ) .
The hormone secretion pattern o f the corpus luteum difers
from that of the follicle (see Fig. 5- 1 ) . As depicted in Figure 5-2,
the greater capacity of granulosa-lutein cells to produce progester­
one results from enhanced access to considerably more steroido­
genic precursors through blood-borne, low-densiry lipoprotein
(LDL)-derived cholesterol (Carr, 1 98 1 a) . Ovarian progesterone
production peaks at 25 to 50 mg/d during the midluteal phase.
With pregnancy, the corpus luteum continues progesterone pro­
duction in response to placental human chorionic gonadotropin
(hCG) , which binds to the same receptor as LH.
Estrogen levels follow a more complex pattern of secretion.
Specifically, just after ovulation, estrogen levels decline, but
then exhibit a secondary rise that reaches a peak production of
0.25 mg/d of 1 73-estradiol in the midluteal phase. Toward the
end of the luteal phase, estradiol production again drops.
The human corpus luteum is a transient endocrine organ
that, in the absence of pregnancy, will rapidly regress 9 to
1 1 days after ovulation via apoptosis (Vaskivuo, 2002) . The
mechanisms that control luteolysis, that is, the regression of
the corpus luteum, remain unclear. However, it results in part
from dropping levels of circulating LH in the late luteal phase
and rising LH insensitivity by luteal cells (Duncan, 1 996; Fili­
cori, 1 986) . he role of other factors is less established. The
dramatic drop in circulating estradiol and progesterone levels
initiate molecular events that lead to menstruation.
Estrogen is the essential hormonal signal on which most events
in the normal menstrual cycle depend. They function in many
cell types to regulate follicular development, uterine receptivity,
and blood flow. The most biologically potent naturally occur­
ring estrogen is 1 73-estradiol, which is secreted by granulosa
cells of the dominant follicle and luteinized granulosa cells of
the corpus luteum. Estradiol action is complex and appears
to involve wo classic nuclear hormone receptors designated
estrogen receptor a (ERa) and 3 (ER3) (Katzenellenbogen,
200 1 ) . These isoforms are the products of separate genes and
can exhibit distinct tissue expression. Both estradiol-receptor
complexes act as transcriptional factors that become associ­
ated with the estrogen-response element of speciic genes. They
share a robust activation by estradiol. However, diferences in
their binding ainities to other estrogens and their cell-speciic
expression pattens suggest that ERa and ER3 receptors
may have both distinct and overlapping function (Saunders,
2005) .
Most progesterone actions on the female reproductive tract
are mediated through the nuclear hormone receptors, proges­
terone-receptor type A (PR-A) and B (PR-B) . Progesterone
enters cells by difusion, and in responsive tissues it becomes
associated with its receptors (Conneely, 2002) . Progesterone­
receptor isoforms arise from a single gene and regulate tran­
scription of target genes. hese receptors have unique actions.
When PR-A and PR-B receptors are coexpressed, it appears
that PR-A can inhibit PR-B gene regulation. The endometrial
glands and stroma appear to have diferent expression patterns
for progesterone receptors that vary during the menstrual cycle
(Mote, 1 999).
Progesterone can also evoke rapid responses, such as changes
in intracellular free calcium levels, which cannot be explained
by genomic mechanisms. G-protein-coupled membrane recep­
tors for progesterone have been identiied, but their role in the
ovarian-endometrial cycle remains to be elucidated (Peluso,
2007) .
• Endometrial Cycle
Pro l iferative Phase
In the endometrium, epithelial cells line the endometrial glands
and are supported by stromal cells. These cells and supplying
blood vessels replicate rapidly and cyclically in reproductive­
aged women and are regenerated each ovarian-endometrial
cycle. The superficial endometrium, termed the functionalis
layer, is shed and reconstructed from the deeper basalis layer
(Fig. 5-4) . There is no other example in humans of such cyclical
shedding and regrowth of an entire tissue.
Fluctuations in estrogen and progesterone levels produce
striking efects on the endometrium. Follicular-phase estradiol
production is the most important factor in endometrial recov­
ery following menstruation, and both ERa and ER3 receptors
are expressed here. Although up to rwo thirds of the functiona­
lis endometrium is fragmented and shed with menses, reepithe­
lialization begins even before menstrual bleeding has ceased. By
the fifth day of the endometrial cycle-ifth day of menses-the
83
84
P lacentati on , E m b ryog enesis, a n d Feta l Deve lopment
Early prol iferative
phase
EPitheli u m
Capi llaries
Late prol iferative
phase
Secretory
phase
Uterine
l umen
�
�-_-..
..�
-
Venous sinus
Functionalis
layer
Endometrial gland --·
S p iral artery -------��-�_.�I'
Basal artery --------�-\\
Basalis layer
Radial artery ---I
Myometriu m
FIGURE 5-4 The endometri u m consists of two layers, the fu nction a l i s l ayer a n d basa lis layer. These a re su p plied by the spira l a n d basa l
a rteries, respective ly. N u merous g l a n d s a lso s pa n these layers. As the menstru a l cycle prog resses, g reater coi l i n g of the spira l a rteries and
i ncreased gland fo l d i ng ca n be seen. Near the end of the menstru a l cycle (day 27), the coiled a rteries constrict, deprive blood su pply to the
fu nctiona l i s layer, a nd lead to necrosis and slou g h i ng of this layer.
epithelial surface of the endometrium has been restored, and
revascularization has begun. he preovulatory endometrium is
characterized by proliferation of glandular, stromal, and vas­
cular endothelial cells. During the early part of the prolifera­
tive phase, the endometrium is usually less than 2 mm thick.
he glands are narrow, tubular structures that pursue almost a
straight and parallel course from the basalis layer toward the
endometrial cavity. Mitotic igures, especially in the glandular
epithelium, are identiied by the fifth cycle day. Mitotic activity
in both epithelium and stroma persists until day 1 6 to 1 7, that
is, 2 to 3 days after ovulation. Blood vessels are numerous and
prominent.
Clearly, reepithelialization and angiogenesis are impor­
tant to cessation of endometrial bleeding (Chennazhi, 2009;
Rogers, 2009) . hese are dependent on tissue regrowth, which
is estrogen regulated. Epithelial cell growth also is regulated in
part by epidermal growth factor and transforming growth fac­
tor a (TGPa) . Stromal cells proliferate through paracrine and
autocrine actions of estrogen and greater local levels of fibro­
blast growth factor-9 (Tsai, 2002) . Estrogens also raise local
production of VEGF, which causes angiogenesis through vessel
elongation in the basalis (Gargett, 200 1 ; Sugino, 2002) .
By the late proliferative phase, the endometrium thickens
from both glandular hyperplasia and augmented stromal
ground substance, which is edema and proteinaceous material.
he loose stroma is especially prominent, and the glands in the
functionalis layer are widely separated. his is compared with
those of the basalis layer, in which the glands are more crowded
and the stroma is denser.
At midcycle, as ovulation nears, glandular epithelium
becomes taller and pseudostratiied. he surface epithelial cells
acquire numerous microvilli, which increase epithelial surface
area, and develop cilia, which move endometrial secretions
during the secretory phase (Perenczy, 1 976) .
Secreto ry P hase
After ovulation, the estrogen-primed endometrium responds to
rising progesterone levels in a highly predictable manner. By
day 1 7, glycogen accumulates in the basal portion of glandular
epithelium, creating subnuclear vacuoles and pseudostratifica­
tion. hese changes likely result from direct progesterone action
through receptors expressed in glandular cells (Mote, 2000) .
On day 1 8, vacuoles move to the apical portion of the secre­
tory non ciliated cells. By day 1 9, these cells begin to secrete
glycoprotein and mucopolysaccharide contents into the gland
lumen (Hafez, 1 975) . Glandular cell mitosis ceases with secre­
tory activity due to rising progesterone levels, which antagonize
the mitotic efects of estrogen. Estradiol action also dimin­
ishes because of glandular expression of the type 2 isoform of
1 73-hydroxysteroid dehydrogenase. his converts estradiol to
the less active estrone (Casey, 1 996) . On cycle days 2 1 to 24,
the stroma becomes edematous. Next, on days 22 to 25, stro­
mal cells surrounding the spiral arterioles begin to enlarge, and
stromal mitosis becomes apparent. Days 23 to 28 are character­
ized by pre decidual cells, which surround spiral arterioles.
Between days 22 and 25, the secretory-phase endometrium
undergoes striking changes associated with predecidual trans­
formation of the upper two thirds of the functionalis layer. The
glands exhibit extensive coiling, and luminal secretions become
visible. Changes within the endometrium also can mark the
so-called window of implantation seen on days 20 to 24. Epi­
thelial surface cells show fewer microvilli and cilia, but lumi­
nal protrusions appear on the apical cell surface (Nikas, 2003) .
hese pinopodes help prepare for blastocyst implantation. hey
I m p l a ntation a n d Place nta l Deve l o p m e n t
also coincide with changes in the surface glycocalyx that allow
acceptance of a blastocyst (Aplin, 2003) .
Another highlight of the secretory phase is the continuing
growth and development of the spiral arteries. hese vessels
arise from the radial arteries, which are myometrial branches
of the arcuate and, ultimately, uterine vessels (see Fig. 5-4).
he morphological and functional properties of the spiral arter­
ies are unique and essential to blood flow changes seen during
menstruation or implantation. During endometrial growth,
spiral arteries lengthen at a rate appreciably greater than the
rate of endometrial tissue thickening. his growth discordance
obliges even greater coiling. Spiral artery development relects
a marked induction of angiogenesis, with widespread vessel
sprouting and extension. Such rapid angiogenesis is regulated,
in part, through estrogen- and progesterone-regulated synthesis
of VEGF (Ancelin, 2002; Chennazhi, 2009) .
Menstru ati on
The midluteal-secretory phase of the endometrial cycle is a
critical branch point in endometrial development and diferen­
tiation. With corpus luteum rescue and continued progesterone
secretion, the endometrium is transformed into the decidua.
With luteolysis and declining luteal progesterone production,
events leading to menstruation are initiated (Critchley, 2006;
Thiruchelvam, 20 1 3) .
In the late premenstrual-phase endometrium, the stroma is
invaded by neutrophils to create a pseudo inflammatory appear­
ance. These cells iniltrate primarily on the day or two imme­
diately preceding menses onset. he endometrial stromal and
epithelial cells produce interleukin-8 (IL-8), a chemotactic-acti­
vating factor for neutrophils (Arici, 1 993) . Similarly, monocyte
chemotactic protein- 1 (MCP- 1 ) is synthesized by endometrium
and promotes monocyte recruitment (Arici, 1 995).
Leukocyte iniltration is considered key to both endometrial
extracellular matrix breakdown and repair of the functionalis
layer. The term "inflammatory tightrope" refers to the ability
of macrophages to assume phenotypes that vary from proin­
flammatory and phagocytic to immunosuppressive and repara­
tive. These are likely relevant to menstruation, in which tissue
breakdown and restoration occur simultaneously (Evans, 20 1 2;
Maybin, 20 1 5) . Invading leukocytes secrete enzymes that are
members of the matrix metalloprotease (MMP) family. These
add to the proteases already produced by endometrial stromal
cells and efectively initiate matrix degradation. During menses
as tissue shedding is completed, microenvironment-regulated
changes in macrophage phenotype then promote repair and
resolution (Evans, 20 1 2; Thiruchelvam, 20 1 3) .
The classic study b y Markee ( 1 940) described tissue and
vascular alterations in endometrium before menstruation.
With endometrial regression, spiral artery coiling becomes
suiciently severe that resistance to blood fl o w rises to cause
endometrial hypoxia. Resultant stasis is the primary cause of
endometrial ischemia and tissue degeneration. Intense spiral
artery vasoconstriction precedes menstruation and also serves
to limit menstrual blood loss.
Prostaglandins play a key role in the events leading to men­
struation that include vasoconstriction, myometrial contractions,
and upregulation of proinflammatory responses (Abel, 2002) .
Large amounts of prostaglandins are present in menstrual blood.
Painful menstruation is common and likely caused by myome­
trial contractions and uterine ischemia. This response is believed
to be mediated by prostaglandin F 2a (PGF2a)-induced spiral
artery vasoconstriction, which render the uppermost endo­
metrial zones hypoxic. The hypoxic environment is a potent
inducer of angiogenesis and vascular permeability factors such
as VEGF.
Progesterone withdrawal increases expression of cyclooxy­
genase 2 (COX-2) , also called prostaglandin synthase 2, to
synthesize prostaglandins. Withdrawal also lowers expression
of 1 5-hydroxyprostaglandin dehydrogenase (PGDH) , which
degrades prostaglandins (Casey, 1 980, 1 989). The net result is
higher prostaglandin production by endometrial stromal cells
and greater prostaglandin-receptor density on blood vessels and
surrounding cells.
Actual menstrual bleeding follows rupture of spiral arteri­
oles and consequent hematoma formation. With a hematoma,
the superficial endometrium is distended and ruptures. S ubse­
quently, fissures develop in the adjacent functionalis layer, and
blood and tissue fragments are sloughed. Hemorrhage stops
with arteriolar constriction. Changes that accompany partial
tissue necrosis also serve to seal vessel tips.
he endometrial surface is restored by growth of langes,
or collars, that form the everted free ends of the endometrial
glands (Markee, 1 940) . These flanges rapidly grow in diameter,
and epithelial continuity is reestablished by fusion of the edges
of these sheets of migrating cells.
DECIDUA
his is a specialized, highly modiied endometrium of preg­
nancy. It is essential for hemochorialplacentation, that is, o ne in
which maternal blood contacts trophoblasts. This relationship
requires trophoblast invasion, and considerable research has
focused on the interaction between decidual cells and invading
trophoblasts. Decidualization, that is, transformation of pro­
liferating endometrial stromal cells into specialized secretory
cells, is dependent on estrogen, progesterone, androgens, and
factors secreted by the implanting blastocyst (Gibson, 2 0 1 6) .
The decidua produces factors that regulate endometrial recep­
tivity and modulate immune and vascular cell functions within
the maternal-fetal microenvironment. The special relationship
existing between the decidua and the invading trophoblasts
ensures success of the pregnancy semiallograft yet seemingly
deies the laws of transplantation immunology.
• Decidual Structure
The decidua is classiied into three parts based on anatomical
location. Decidua directly beneath blastocyst implantation is
modiied by trophoblast invasion and becomes the decidua
basalis. The decidua capsularis overlies the enlarging blasto­
cyst and initially separates the conceptus from the rest of the
uterine cavity (Fig. 5-5) . This portion is most prominent dur­
ing the second month of pregnancy and consists of stromal
decidual cells covered by a single layer of lattened epithelial
cells. Internally, it contacts the avascular, extraembryonic fetal
85
86
P l ace ntat i o n , E m b ryogenesis, a n d Feta l Development
parietal is
Decidua basalis ---.f
Chorionic
villi
cavity
Cervical
canal
FIGURE 5-5 Th ree portions of the decidua-the basa l is, capsu­
l a ri s, and pa rieta l is-are i l l ustrated .
membrane-the chorion laeve. he remainder of the uterus is
lined by decidua parietalis. During early pregnancy, there is a
space between the decidua capsularis and parietalis because the
gestational sac does not fill the entire uterine cavity. The gesta­
tion sac is the extraembryonic coelom and also called the cho­
rionic cavity. By 1 4 to 1 6 weeks' gestation, the expanding sac
has enlarged to completely ill the uterine cavity. The resulting
apposition of the decidua capsularis and parietalis creates the
decidua vera, and the uterine cavity is functionally obliterated.
In early pregnancy, the decidua begins to thicken, eventu­
ally attaining a depth of 5 to 1 0 mm. With magnification, fur­
rows and numerous small openings, representing the mouths of
uterine glands, can be detected. Later in pregnancy, the decidua
becomes thinner, presumably because of pressure exerted by the
expanding uterine contents.
he decidua parietalis and basalis are composed of three
layers. here is a surface or compact zone-zona compacta; a
middle portion or spongy zone-zona spongiosa-with rem­
nants of glands and numerous small blood vessels; and a basal
zone-zona basalis. The zona compacta and spongiosa together
form the zona functionalis. The basal zone remains after delivery
and gives rise to new endometrium.
In human pregnancy, the decidual reaction is completed
only with blastocyst implantation. Predecidual changes, how­
ever, commence irst during the midluteal phase in endome­
trial stromal cells adjacent to the spiral arteries and arterioles.
hereafter, they spread in waves throughout the uterine endo­
metrium and then from the implantation site. The endometrial
stromal cells enlarge to form polygonal or round decidual cells.
he nuclei become vesicular, and the cytoplasm becomes clear,
slightly basophilic, and surrounded by a translucent membrane.
As a consequence of implantation, the blood supply to the
decidua capsularis is lost as the embryo-fetus grows. Blood
supply to the decidua parietalis through spiral arteries persists.
These arteries retain a smooth-muscle wall and endothelium
and thereby remain responsive to vasoactive agents.
In contrast, the spiral arterial system that supplies the
decidua basalis and ultimately the placental intervillous space
is altered remarkably. These spiral arterioles and arteries are
invaded by trophoblasts, and during this process, the vessel
walls in the basalis are destroyed. Only a shell without smooth
muscle or endothelial cells remains. Importantly, as a result,
these vascular conduits of maternal blood-which become the
uteroplacental vessels-are unresponsive to vasoactive agents.
Conversely, the fetal chorionic vessels, which transport blood
between the placenta and the fetus, contain smooth muscle and
thus do respond to vasoactive agents.
• Decidual Histology
Early in pregnancy, the zona spongiosa of the decidua consists
of large distended glands, often exhibiting marked hyperplasia
and separated by minimal stroma. At first, the glands are lined
by typical cylindrical uterine epithelium with abundant secre­
tory activity that contributes to blastocyst nourishment. With
advanced pregnancy, the glandular elements largely disappear.
he decidua basalis contributes to formation of the pla­
cental basal plate (Fig. 5-6) . he spongy zone of the decidua
basalis consists mainly of arteries and widely dilated veins, and
by term, glands have virtually disappeared. Also, the decidua
basalis is invaded by many interstitial trophoblasts and tropho­
blastic giant cells. Although most abundant in the decidua, the
giant cells commonly penetrate the upper myometrium. Their
number and invasiveness can be so extensive as to resemble
choriocarcinoma.
The Nitabuch layer is a zone of fibrinoid degeneration in
which invading trophoblasts meet the decidua basalis. If the
Decidua
FIGU RE 5-6 Section thro u g h a j u n ction of chorion, vi l l i, and
decid ua basa lis i n early first-trimester p reg n a ncy. (Used with
permission from Dr. Kurt Ben i rsc h ke.)
I m p la ntation a n d P l acenta l Develop ment
decidua is defective, as in placenta accreta, the Nitabuch layer
is usually absent (Chap. 4 1 , p. 778) . here is also a more super­
icial, but inconsistent, deposition of ibrin-Rohr stria-at the
bottom of the intervillous space and surrounding the anchoring
villi. Decidual necrosis is a normal phenomenon in the irst and
probably second trimesters (McCombs, 1 964) . hus, necrotic
decidua obtained through curettage after spontaneous abortion
in the irst trimester should not necessarily be interpreted as
either a cause or an efect of the pregnancy loss.
Both decidua types contain numerous cell groups whose
composition varies with gestational stage (Loke, 1 995) . he
primary cellular components are the true decidual cells, which
diferentiated from the endometrial stromal cells, and numer­
ous maternal bone marrow-derived cells. Accumulation of lym­
phocytes with unique properties at the maternal-fetal interface
is essential to evoke tolerance mechanisms that prevent mater­
nal immune rejection of the fetus. These include regulatolY T
cells, decidual macrophages, and decidual natural killer cells.
Collectively, these cells not only provide immunotolerance but
also play an important role in trophoblast invasion and vascu­
logenesis (PrabhuDas, 20 1 5) .
• Decidual Prolactin
In addition to placental development, the decidua potentially
provides other functions. The decidua is the source of prolac­
tin, which is present in enormous amounts in amnionic luid
(Colander, 1 978; Riddick, 1 979) . Decidual prolactin is a prod­
uct of the same gene that encodes for anterior pituitary pro­
lactin, but the exact physiological role of decidual prolactin is
unknown. Notably, decidual prolactin is not to be confused
with placental lactogen (hPL) , which is produced only by syn­
cytiotrophoblast.
Prolactin preferentially enters amnionic luid, and little
enters maternal blood. Consequently, prolactin levels in amni­
onic luid are extraordinarily high and may reach 1 0,000 ng/mL
at 20 to 24 weeks' gestation (Tyson, 1 972) . This compares with
fetal serum levels of 350 ng/mL and maternal serum levels of
1 50 to 200 ngl mL. As a result, decidual prolactin is a clas­
sic example of paracrine function between maternal and fetal
tissues.
mother and for maternal immunological acceptance of the con­
ceptus (Cuzeloglu-Kayisli, 2009) .
• Fertilization
With ovulation, the secondary oocyte and adhered cells of the
cumulus-oocyte complex are freed from the ovary. Although
technically this mass of cells is released into the peritoneal cav­
ity, the oocyte is quickly engulfed by the fallopian tube infun­
dibulum. Further transport through the tube is accomplished
by directional movement of cilia and tubal peristalsis. Fertiliza­
tion, which normally occurs in the oviduct, must take place
within a few hours, and no more than a day after ovulation.
Because of this narrow window, spermatozoa must be p resent
in the fallopian tube at the time of oocyte arrival. Almost all
pregnancies result when intercourse occurs during the 2 days
preceding or on the day of ovulation.
Fertilization is highly complex. Molecular mechanisms allow
spermatozoa to pass between follicular cells; through the zona
pellucida, which is a thick glycoprotein layer surrounding the
oocyte cell membrane; and into the oocyte cytoplasm. F usion
of the two nuclei and intermingling of maternal and paternal
chromosomes creates the zygote.
Early human development is described by days or weeks
postfertilization, that is, postconceptional. By contrast, in most
chapters of this book, clinical pregnancy dating is calculated
from the irst day of the last menstrual period (LMP) . hus,
1 week postfertilization corresponds to approximately 3 weeks
from the LMP in women with regular 28-day cycles. As an
example, 8 weeks' gestation refers to 8 completed weeks fol­
lowing the LMP.
After fertilization, the zygote-a diploid cell with 46 chro­
mosomes-undergoes cleavage, and zygote cells produced by
this division are called blastomeres (Fig. 5-7) . In the two-cell
IMPLANTATION AND EARLY
TROPHOBLAST FORMATION
The ferus is dependent on the placenta for pulmonary, hepatic,
and renal functions. These are accomplished through the ana­
tomical relationship of the placenta and its uterine interface.
In overview, maternal blood spurts from uteroplacental vessels
into the placental intervillous space and bathes the outer syn­
cytiotrophoblast. his allows exchange of gases, nutrients, and
other substances with fetal capillary blood within the core of
each villus. hus, fetal and maternal blood does not normally
mix in this hemochorial placenta. A paracrine system also links
mother and ferus through the anatomical and biochemical jux­
taposition of the maternal decidua parietalis and the extraem­
bryonic chorion laeve, which is fetal. This is an extraordinarily
important arrangement for communication between fetus and
1 6-cel l stage ( Moru la)
Blastocyst
I n n e r cell
mass
Blastocyst
cavity
Trophoblast
FIGURE 5-7 Zyg ote cleavage a nd blastocyst formation. The
moru la period beg i ns at the 1 2- to 1 6-cell stage and ends when
the blastocyst forms, which occu rs when there a re 50 to 60 b las­
tomeres present. The p o l a r bod ies, shown i n the 2-ce l l stage, a re
s m a l l nonfu nction a l cel l s that soon degenerate.
87
88
P lacentation, E m b ryogen esis, a n d Feta l Devel opment
zygote, the blastomeres and polar body continue to be sur­
rounded by the zona pellucida. he zygote undergoes slow
cleavage for 3 days while still remaining in the fallopian tube.
As the blastomeres continue to divide, a solid mulberry-like
ball of cells-the morula-is produced. The morula enters the
uterine cavity approximately 3 days after fertilization. Gradual
accumulation of luid beween the morula cells leads to forma­
tion of the early blastocyst.
• Blastocyst
As early as 4 to 5 days after fertilization, the 5 8-cell blastula
diferentiates into ive embryo-producing cells-the inner cel
mass (see Fig. 5-7) . he remaining 53 outer cells, called the
trophectoderm, are destined to form trophoblasts (Hertig, 1 962) .
Interestingly, the 1 07 -cell blastocyst is found to be no larger
than the earlier cleavage stages, despite the accumulated fluid
within the blastocyst cavity. At this stage, the eight formative,
embryo-producing cells are surrounded by 99 trophoblastic
cells. And, the blastocyst is released from the zona pellucida
secondary to secretion of specific proteases from the secretory­
phase endometrial glands (O'Sullivan, 2002) .
Release from the zona pellucida allows blastocyst-produced
cytokines and hormones to directly influence endometrial
receptivity (Lindhard, 2002) . IL- l a and I L- l j are secreted by
the blastocyst, and these cytokines likely directly influence the
endometrium. Embryos also have been shown to secrete hCG,
which may influence endometrial receptivity (Licht, 200 1 ;
Lobo, 200 1 ) . The receptive endometrium i s thought to respond
by producing leukemia inhibitoY factor (LIF), follistatin, and
colony-stimulating factor- l (CSF- l ) . LIF and follistatin acti­
vate signaling pathways that collectively inhibit proliferation
and promote diferentiation of the endometrial epithelia and
stroma to enable uterine receptivity (Rosario, 20 1 6b) . At the
maternal-fetal interface, CSF- 1 has proposed immunomodu­
latory actions and pro angiogenic actions that are required for
implantation (Rahmati, 20 1 5) .
• Implantation
Six or 7 days after fertilization, the blastocyst implants into the
uterine wall. This process can be divided into three phases: ( 1 )
apposition-initial contact o f the blastocyst t o the uterine wall;
(2) adhesion-increased physical contact between the blasto­
cyst and decidua; and (3) invasion-penetration and invasion
of syncytiotrophoblast and cytotrophoblasts into the decidua,
inner third of the myometrium, and uterine vasculature.
Successful implantation requires a receptive endometrium
appropriately primed with estrogen and progesterone by the
corpus luteum. Such uterine receptivity is limited to days 20 to
24 of the cycle. Adherence is mediated by cell-surface receptors
at the implantation site that interact with blastocyst receptors
(Carson, 2002; Lessey, 2002; Lindhard, 2002) . If the blastocyst
approaches the endometrium after cycle day 24, the potential
for adhesion is diminished because antiadhesive glycoprotein
synthesis prevents receptor interactions (N avot, 1 99 1 ) .
At the time o f its interaction with the endometrium, the
blastocyst is composed of 1 00 to 250 cells. The blastocyst
loosely adheres to the decidua by apposition. This most com­
monly occurs on the upper posterior uterine wall. Attachment
of the blastocyst trophectoderm to the decidual surface by
apposition and adherence appears to be closely regulated by
paracrine interactions between these two tissues.
Successful endometrial blastocyst adhesion involves modi­
ication in expression of cellular adhesion molecules (CMs) .
The integrins-one of four families of CAMs-are cell-surface
receptors that mediate cell adhesion to extracellular matrix
proteins (Lessey, 2002) . Endometrial integrins are hormonally
regulated, and a specific set of integrins is expressed at implan­
tation (Lessey, 1 995). Recognition-site blockade of integrins
needed for binding will prevent blastocyst attachment (Kaneko,
20 1 3) .
• Trophoblast Development
Human placental formation begins with the trophectoderm,
which gives rise to a trophoblast cell layer encircling the blas­
tocyst. From then until term, trophoblasts play a critical part at
the fetal-maternal interface. Trophoblasts exhibit the most vari­
able structure, function, and developmental pattern of all pla­
cental components. Their invasiveness promotes implantation,
their nutritional role for the conceptus is relected in their name,
and their endocrine organ function is essential to maternal phys­
iological adaptations and to pregnancy maintenance.
By the eighth day postfertilization, after initial implantation,
trophoblasts have diferentiated into an outer multinucleated
syncytium-primitive syncytiotrophoblast, and an inner layer
of primitive mononuclear cells-cytotrophoblasts. The latter are
germinal cells for the syncytium. As cytotrophoblasts prolifer­
ate, their cell walls disappear, and the cells fuse to add to the
expanding outer layer of syncytiotrophoblast. Each cytotro­
phoblast has a well-demarcated cell border, a single nucleus,
and ability to undergo DNA synthesis and mitosis (Arnholdt,
1 99 1 ) . These are lacking in the syncytiotrophoblast, which pro­
vides transport functions of the placenta. It is so named because
instead of individual cells, it has an amorphous cytoplasm with­
out cell borders, nuclei that are multiple and diverse in size and
shape, and a continuous syncytial lining. This coniguration
aids transport.
After implantation is complete, trophoblasts further dif­
ferentiate along two main pathways, giving rise to villous and
extravillous trophoblasts. As shown in Figure 5-8, both have
distinct functions (Loke, 1 995). Villous trophoblasts generate
chorionic villi, which primarily transport oxygen, nutri­
ents, and other compounds between the fetus and mother.
Extravillous trophoblasts migrate into the decidua and myo­
metrium and also penetrate maternal vasculature, thus com­
ing into contact with various maternal cell types (Pijnenborg,
1 994) . Extravillous trophoblasts are further classiied as inter­
stitial trophoblasts and endovascular trophoblasts. he intersti­
tial trophoblasts invade the decidua and eventually penetrate
the myometrium to form placental-bed giant cells. These
trophoblasts also surround spiral arteries. The endovascular
trophoblasts penetrate the spiral artery lumens (Pijnenborg,
1 983) . hese are both discussed in greater detail in subse­
quent sections.
I m p l a ntation a n d Placenta l Deve l o p ment
Anchoring villus
Syncytiotrophoblast
Cytotrophoblast
Extravi l lous trophoblasts
Endothelium
�
�"
I nterstitial extravillous trophoblast
Endovascu lar extravillous trophoblast
� �
o
l
-
Decidua
-j
..
"
.
basalis
-
Spiral artery ---1
Myometri u m
M idgestation
End of 1 st
Early
3rd tri mester
trimester
pregnancy
FIGURE 5-8 Extravi l lous trophoblasts a re found outside the vi l l u s a n d ca n be su bd ivided into endovascular a n d interstitia l categories.
Endovasc u l a r trophoblasts i nvade and tra n sform spira l a rteries d u ri n g preg nancy to create low-resi sta nce blood flow that i s c h a racteri stic of
the placenta. I nterstitial trophoblasts i nvade the decidua and s u rro u n d spiral a rteries.
• Early I nvasion
After gentle erosion between epithelial cells of the surface endo­
metrium, invading trophoblasts burrow deeper. At 9 days of
development, the blastocyst wall facing the uterine lumen is a
single layer of lattened cells. By the 1 0th day, the blastocyst
becomes totally encased within the endometrium (Fig. 5-9) . he
blastocyst wall opposite the uterine lumen is thicker and com­
prises two zones-the trophoblasts and the embryo-forming
inner cell mass. As early as 7Y2 days postfertilization, the inner
cell mass or embryonic disc diferentiates into a thick plate of
primitive ectoderm and an underlying layer of endoderm. Some
small cells appear between the embryonic disc and the tropho­
blasts and enclose a space that will become the amnionic cavity.
Extraembryonic mesenchyme first appears as groups of
isolated cells within the blastocyst cavity, and later this meso­
derm completely lines the cavity. Spaces form and then fuse
within the extraembryonic mesoderm to form the cho rionic
cavity (extraembryonic coelom) . The chorion is composed of
trophoblasts and mesenchyme. Some mesenchymal cells even­
tually will condense to form the body stalk. his stalk joins
the embryo to the nutrient chorion and later develops into the
umbilical cord. The body stalk can be recognized at an early
stage at the caudal end of the embryonic disc (Fig. 7-3, p. 1 26) .
As the embryo enlarges, more maternal decidua basalis is
invaded by syncytiotrophoblast. Beginning approximately
1 2 days after conception, the syncytiotrophoblast is permeated
Spiral artery
Maternal blood
Lacunar network
Amnionic
cavity
Lacunar network
Syncytiotrophoblast
Amnion
E m bryonic disc
E xtraembryon ic
e ndoderm
Extraem bryonic
mesoderm
A
Primitive
yolk sac
B
FIGURE 5-9 Drawi ng of sections thro u g h i m p l a nted blastocysts. A. At 1 0 days. B. At 1 2 days ater ferti l ization. This stage i s cha racterized
by the i ntercom m u n ication of the lacu nae fi l led with maternal blood. Note in (B) that l a rge cavities have appeared in the extraem bryon i c
mesoderm, forming t h e beg i n n i n g o f t h e extraembryon ic coelom. A l s o note that extraem bryon ic endoderm a l cells h a v e beg u n t o for m
on t h e i nside o f t h e prim itive yol k sac. (Red rawn from Moore KL, Persaud, W, Torchia, MG (ed s): The Developing H u m a n. C l i n ica l l y Oriented
Embryology, 9th edition, P h i ladelphia, Sa u nders, 201 3.)
89
90
P lace ntati o n , E m b ryoge nesis, a n d Feta l Develop m e nt
by a system of intercommunicating channels called trophoblas­
tic lacunae. After invasion of supericial decidual capillary walls,
lacunae become filled with maternal blood. At the same time,
the decidual reaction intensifies in the surrounding stroma.
This is characterized by decidual stromal cell enlargement and
glycogen storage.
• Chorionic Villi
With deeper blastocyst invasion into the decidua, solid primary
villi arise from buds of cytotrophoblasts that protrude into the
primitive syncytium before 1 2 days postfertilization. Primary villi
are composed of a cytotrophoblast core covered by syncytiotro­
phoblast. s the lacunae join, a complicated labyrinth is formed
that is partitioned by these solid cytotrophoblastic columns. The
trophoblast-lined channels form the intervillous space, and the
solid cellular columns form the primay villous stalks.
Beginning on approximately the 1 2th day after fertilization,
mesenchymal cords derived from extraembryonic mesoderm
invade the solid trophoblast columns. These form seconday
villi. Once angiogenesis begins in the mesenchymal cords, ter­
tiay villi are formed. Although maternal venous sinuses are
tapped early in implantation, maternal arterial blood does not
enter the intervillous space until around day 1 5 . By approxi­
mately the 1 7th day, however, fetal blood vessels are functional,
and a placental circulation is established. The fetal-placental
circulation is completed when the blood vessels of the embryo
are connected with chorionic vessels. In some villi, angiogen­
esis fails from lack of circulation. They can be seen normally,
but the most striking exaggeration of this process is seen with
hydatidiform mole (Fig. 20- 1 , p. 389) .
Villi are covered by an outer layer of syncytiotrophoblast
and an inner layer of cytotrophoblasts, which are also known as
Langhans cels. Cytotrophoblast proliferation at the villous tips
produces the trophoblastic cell columns that form anchoring
villi. hey are not invaded by fetal mesenchyme, and they are
anchored to the decidua at the basal plate. Thus, the base of the
intervillous space faces the maternal side and consists of cyto­
trophoblasts from cell columns, the covering shell of syncytio­
trophoblast, and maternal decidua of the basal plate. The base
of the chorionic plate forms the roof of the intervillous space.
It consists of two layers of trophoblasts externally and fibrous
mesoderm internally. The "deinitive" chorionic plate is formed
by 8 to 1 0 weeks as the amnionic and primary chorionic plate
mesenchyme fuse together. This formation is accomplished by
expansion of the amnionic sac, which also surrounds the con­
nective stalk and the allantois and joins these structures to form
the umbilical cord (Kaufmann, 1 992) .
Interpretation of the ine structure of the placenta came
from electron microscopic studies of Wislocki and Dempsey
( 1 9 5 5 ) . There are prominent microvilli on the syncytial sur­
face that correspond to the so-called brush border described by
light microscopy. Associated pinocytotic vacuoles and vesicles
are related to absorptive and secretory placental functions.
Microvilli act to increase surface area in direct contact with
maternal blood. This contact between the trophoblast and
maternal blood is the deining characteristic of a hemochorial
placenta (Fig. 5- 1 0) .
Intervillous
space
FIGURE 5-1 0 Electron m icrog ra ph of term h u m a n placenta v i l l u s.
A vi l l us ca p i l l a ry fi l led with fetal red blood cel l s (asterisks) is seen i n
close proxim ity t o the microvi l l i border. (Reprod uced with permis­
sion from Boyd J D, H a m i lton WJ: The H u m a n Placenta. Cam bridge,
Heffer, 1 970.)
PLACENTA AND CHORION
• Chorion Development
In early pregnancy, the villi are distributed over the entire
periphery of the chorionic membrane (Fig. 5- 1 1 ) . As the blasto­
cyst with its surrounding trophoblasts grows and expands into
the decidua, one pole faces the endometrial cavity. he opposite
pole will form the placenta. Here, chorionic villi in contact with
the decidua basalis proliferate to form the chorion rondosum­
or leay chorion. As growth of embryonic and extraembryonic
tissues continues, the blood supply to the chorion facing the
endometrial cavity is restricted. Because of this, villi in contact
with the decidua capsularis cease to grow and then degenerate.
his portion of the chorion becomes the avascular fetal mem­
brane that abuts the decidua parietalis and is called the chorion
laeve-or smooth chorion. This smooth chorion is composed of
cytotrophoblasts and fetal mesodermal mesenchyme.
Until near the end of the third month, the chorion laeve is
separated from the amnion by the exocoelomic cavity. hereater,
they are in intimate contact to form an avascular amniochorion.
These two structures are important sites of molecular transfer and
metabolic activity. Moreover, they constitute an important para­
crine arm of the fetal-maternal communication system.
• Regulators of Trophoblast I nvasion
Implantation and endometrial decidualization activate a unique
population of maternal immune cells that iniltrate the uterus
I m pla ntati o n a n d Placental Develop m ent
for approximately 20 percent of leukocytes in the first trimes­
ter and elicit an M2-immunomodulatory phenotype (Williams,
2009). Remember, M1 macrophages are pro inflammatory, and
M2 macrophages counter proinflammatory responses and promote
tissue repair. In addition to a role in angiogenesis and spiral artery
remodeling, dNK cells promote phagocytosis of cell debris (Faas,
20 1 7). Concurrent with the critical role of maternal dNK cells and
macrophages, T cell subsets aid tolerance toward the allogenic fetus.
Regulatory T cells (Tregs) are essential for promoting immune toler­
ance. Other T cell subsets are present, such s Th 1 , Th2 and Th 1 7,
although their unctions are tightly regulated (Ruocco, 20 14) .
• Endometrial Invasion
B
FIGURE 5-1 1 Com plete abortion specimens. A. I n itial ly, the entire
chorionic sac is covered with vi l l i, a nd the embryo wit h i n is not
visible B. With fu rth e r g rowth, stretch a nd pressu re p rom pt pa rtial
reg ression of the villi. Remai n i ng vi l l i form the future placenta,
whereas the smooth portion i s the chorion.
and play critical functions in trophoblast invasion, angiogenesis,
spiral artery remodeling, and maternal tolerance to fetal alloan­
tigens. Decidual natural killer cells (dNK) make up 70 percent
of decidual leukocytes in the fi r st trimester and are found in
direct contact with trophoblasts. In contrast to natural killer
cells in peripheral blood, these cells lack cytotoxic functions.
They produce specifi c cytokines and angiogenic factors to regu­
late invasion of fetal trophoblasts and spiral artery remodeling
(Hanna, 2006) . hese and other unique properties distinguish
dNK cells from circulating natural killer cells and from natural
killer cells in the endometrium before pregnancy (Fu, 20 1 3 ;
Winger, 20 1 3) . dNK cells express both IL-8 and interferon­
inducible protein- 1 0, which bind to receptors on invasive tro­
phoblastic cells to promote their decidual invasion toward the
spiral arteries. dNK cells also produce proangiogenic factors,
including VEGF and placental growth factor (PIGF), which
both promote vascular growth in the decidua.
Trophoblasts also secrete speciic chemokines that attract the
dNK cells to the maternl-fetal interface. hus, both cell types
simultaneously attract each other. Decidual macro phages account
Extravillous trophoblasts of the first-trimester placenta are highly
invasive. his process occurs under low-oxygen conditions, and
regulatory factors that are induced under hypoxic conditions are
contributory (Soares, 20 1 2) . Invasive trophoblasts secrete numer­
ous proteolytic enzymes that digest extracellular matrix and acti­
vate proteinases already present in the decidua. Trophoblasts
produce urokinase-type plasminogen activator, which converts
plasminogen into the broadly acting serine protease, plasmin.
This in turn both degrades matrix proteins and activates M.1Ps.
One member of the MMP family, MMP-9, appears to be criti­
cal. The timing and extent of trophoblast invasion is regulated by
a balanced interplay between pro- and antiinvasive factors.
he relative ability to invade maternal tissue in early preg­
nancy compared with limited invasiveness in late pregnancy is
controlled by autocrine and paracrine trophoblastic and decid­
ual factors. Trophoblasts secrete insulin-like growth factor II
that promotes invasion into the decidua. Decidual cells secrete
insulin-like growth factor binding-protein type 4, which blocks
this autocrine loop.
Low estradiol levels in the irst trimester are critical for tropho­
blast invasion and remodeling of the spiral arteries. nimal studies
suggest that the rise in second-trimester estradiol levels suppresses
and limits vessel remodeling by reducing trophoblast expression of
VEGF and speciic integrin receptors (Bonagura, 20 1 2) . Namely,
extravillous trophoblasts express integrin receptors that recognize
the extracellular matrix proteins collagen IV, laminin, and ibro­
nectin. Binding of these matrix proteins and integrin receptors
initiates signls to promote trophoblast cell migration and dif­
ferentiation. However, as pregnancy advances, rising estradiol
levels downregulate VEGF and integrin receptor expression. This
represses and controls the extent of uterine vessel transformation.
• Spiral Artery Invasion
One of the most remarkable features of human placental devel­
opment is the extensive modification of maternal vasculature
by trophoblasts, which are by defi n ition of fetal origin. These
events occur in the first half of pregnancy and are considered in
detail because of their importance to uteroplacental blood flow.
They are also integral to some pathological conditions such as
preeclampsia, fetal-growth restriction, and preterm birth. Spi­
ral artery modiications are carried out by two populations of
extravillous trophoblasts-endovascular trophoblasts, which
penetrate the spiral-artery lumen, and interstitial trophoblasts,
which surround the arteries (see Fig. 5-8 ) .
91
92
P l acentation, E m bryogenesis, a n d Feta l Deve l o p m e n t
Interstitial trophoblasts constitute a major portion of the
placental bed. They penetrate the decidua and adjacent myo­
metrium and aggregate around spiral arteries. Although less
defined, their functions may include vessel preparation for
endovascular trophoblast invasion.
Endovascular trophoblasts irst enter the spiral artery lumens
and initially form cellular plugs. They then destroy vascular endo­
thelium via an apoptosis mechanism and invade and modiy the
vascular media. hus, fibrinoid material replaces smooth muscle
and connective tissue of the vessel media. Spiral arteries later
regenerate endothelium. Invading endovascular trophoblasts can
extend several centimeters along the vessel lumen, and they must
migrate against arterial flow. Of note, invasion by trophoblasts
involves only the decidual spiral arteries and not decidual veins.
Uteroplacental vessel development proceeds in two waves
or stages (Ramsey, 1 980) . The irst occurs before 1 2 weeks'
postfertilization, and spiral arteries are invaded and modiied
up to the border between the decidua and myometrium. he
second wave, between 1 2 and 1 6 weeks, involves some invasion
of the intramyometrial segments of spiral arteries. Remodeling
converts narrow-lumen, muscular spiral arteries into dilated,
low-resistance uteroplacental vessels. Molecular mechanisms
of these crucial events, their regulation by cytokines, signaling
pathways, and their significance in the pathogenesis of pre­
eclampsia and fetal-growth restriction has been reviewed by sev­
eral authors (Pereira de Sousa, 20 1 7; ie, 20 1 6; Zhang, 20 1 6) .
Approximately 1 month after conception, maternal blood
enters the intervillous space in fountain-like bursts from the
spiral arteries. Blood is propelled outside of the maternal vessels
and sweeps over and directly bathes the syncytiotrophoblast.
• Villus Branching
Although certain villi of the chorion frondosum extend from
the chorionic plate to the decidua to serve as anchoring villi,
most villi arborize and end freely within the intervillous space.
s gestation proceeds, the short, thick, early stem villi branch
to form progressively iner subdivisions and greater numbers
of increasingly smaller villi (Fig. 5- 1 2) . Each of the truncal or
main stem villi and their ramiications constitutes a placental
F I G U R E 5-1 2 Electron micrographs (A, C) and photo m icrog ra phs (B, D) of early and late h u m a n placentas. A and B. Limited branching of
villi is seen in this ea rly placenta. C and D. With placenta l maturation, i ncreasing vi l lous a rborization is seen, and villous ca pilla ries lie closer to the
su rface of each vi l l us. (Photomicrogra phs u sed with permi ssion from Dr. Kurt Ben i rschke. Electron m icrog ra phs reproduced with permission from
Ki ng BF, Menton DN: Sca nn i ng electron m icroscopy of h u m a n placenta l vi lli from early and late in gestation. Am J Obstet Gynecol 1 22:824, 1 975.)
I m p la ntati o n a n d Placental Deve l o p m ent
lobule, or cotyledon. Each lobule is supplied with a single cho­
rionic artery. And each lobule has a single vein, so that lobules
constitute the functional units of placental architecture.
• Placental Growth and Maturation
In the irst trimester, placental growth is more rapid than that
of the fetus. But by approximately 1 7 weeks' gestation, placen­
tal and fetal weights are approximately equal. By term, placen­
tal weight is approximately one sixth of fetal weight.
he mature placenta and its variant forms are discussed in
detail in Chapter 6 (p. 1 1 2) . Briely, viewed from the mater­
nal surface, the number of slightly elevated convex areas, called
lobes, varies from 1 0 to 38. Lobes are incompletely separated
by grooves of variable depth that overlie placental septa, which
arise as upward projections of decidua. he total number of
placental lobes remains the same throughout gestation, and
individual lobes continue to grow-although less actively in the
inal weeks (Crawford, 1 959). Although grossly visible lobes
are commonly referred to as cotyledons, this is not accurate.
Correctly used, lobules or cotyledons are the functional units
supplied by each main stem villus.
As villi continue to branch and the terminal ramiications
become more numerous and smaller, the volume and promi­
nence of cytotrophoblasts decrease. As the syncytium thins, the
fetal vessels become more prominent and lie closer to the sur­
face (see Fig. 5- 1 0) . he villous stroma also exhibits changes as
gestation progresses. In early pregnancy, the branching connec­
tive-tissue cells are separated by an abundant loose intercellular
matrix. Later, the villous stroma becomes denser, and the cells
are more spindly and closely packed.
Another change in the stroma involves the iniltration of
Hobauer cels, which are fetal macrophages. hese are nearly
round with vesicular, often eccentric nuclei and very granular
or vacuolated cytoplasm. hey grow in number and matura­
tional state throughout pregnancy and appear to be important
mediators of protection at the maternal-fetal interface Qohn­
son, 20 1 2) . These macrophages are phagocytic, have an immu­
nosuppressive phenotype, can produce various cytokines, and
are capable of paracrine regulation of trophoblastic functions
(Cervar, 1 999; Reyes, 20 1 7) . As discussed further in Chapter
64 (p. 1 2 1 9) , recent studies suggest that Zika virus can infect
Hofbauer cells to allow fetal transmission (Simoni, 20 1 7) .
Some o f the histological changes that accompany placental
growth and maturation improve transport and exchange to meet
advancing fetal metabolic requirements. Among these changes are
a thinner syncytiotrophoblst, signiicantly reduced cytotropho­
blast number, decreased stroma, and increased number of capil­
laries with close approximation to the syncytial surface. By 1 6
weeks' gestation, the apparent continuity o f the cytotrophoblasts
is lost. At term, villi may be focally reduced to a thin layer of syn­
cytium covering minimal villous connective tissue in which thin­
walled fetal capillaries abut the trophoblast and dominate the villi.
There are some changes in placental architecture that can
cause decreased placental exchange eiciency if they are sub­
stantive. These include thickening of the basal lamina of tropho­
blast or capillaries, obliteration of certain fetal vessels, greater
villous stroma, and ibrin deposition on the villous surface.
Myometriu m -..:;-
\
Chorion --:U
Amnion -W
Decidua
basalis
Placenta
\. -
-
FIGURE 5-1 3 Uterus showing a normal place nta a nd its mem­
b ra nes i n situ.
• Placental Circulation
Because the placenta is functionally an intimate approximation
of the fetal capillary bed to maternal blood, its gross anatomy
primarily concerns vascular relations. he fetal surface is cov­
ered by the transparent amnion, beneath which chorionic ves­
sels course. A section through the placenta includes amnion,
chorion, chorionic villi and intervillous space, decidual (basal)
plate, and myometrium (Figs. 5- 1 3 and 5- 1 4) .
FIGURE 5-1 4 P h otomicrog ra ph of ea rly i m p l a nted bla stocyst.
Trophoblasts a re seen i nvad i ng the decidua basal is. eNS ce ntra l
nervous system. (Used with perm ission from D r. Kurt Ben i rsch ke.)
=
93
94
Place ntation, E m bryogenesis, a n d Feta l Deve l o p m e nt
Feta l Ci rcu lation
Deoxygenated venous-like fetal blood flows to the placenta
through the two umbilical arteries. As the cord joins the pla­
centa, these umbilical vessels branch repeatedly beneath the
amnion as they run across the chorionic plate. Branching con­
tinues within the villi to ultimately form capillary networks in
the terminal villous branches. Blood with signiicantly higher
oxygen content returns from the placenta via a single umbilical
vein to the fetus.
The branches of the umbilical vessels that traverse along the
fetal surface of the placenta in the chorionic plate are referred
to as the placental surface or chorionic vessels. These vessels
are responsive to vasoactive substances, but anatomically, mor­
phologically, histologically, and functionally, they are unique.
Chorionic arteries always cross over chorionic veins. Vessels
are most readily recognized by this interesting relationship, but
they are diicult to distinguish by histological criteria.
Truncal arteries are perforating branches of the surface arter­
ies that pass through the chorionic plate. Each truncal artery
supplies one main stem villus and thus one cotyledon. As the
artery penetrates the chorionic plate, its wall loses smooth mus­
cle, and its caliber increases. The loss of muscle continues as the
truncal arteries and veins branch into their smaller rami.
Before 10 weeks' gestation, there is no end-diastolic low
pattern within the umbilical artery at the end of the fetal car­
diac cycle (Fisk, 1 988; Loquet, 1 988). After 1 0 weeks, how­
ever, end-diastolic low appears and is maintained throughout
normal pregnancy. Clinically, these fl o w patterns are studied
with Doppler sonography to assess fetal well-being (Chap. 1 0,
p. 2 1 3) .
low-resistance vessels that can accommodate massive increase in
uterine perfusion during gestation. Generally, spiral arteries are
perpendicular to, but veins are parallel to, the uterine wall. his
arrangement aids closure of veins during a uterine contraction
and prevents the exit of maternal blood from the intervillous
space. The number of arterial openings into the intervillous
space is gradually reduced by cytotrophoblastic invasion. here
are about 1 20 spiral arterial entries into the intervillous space
at term (Brosens, 1 963) . hese discharge blood in spurts that
bathes the adjacent villi (Borell, 1 958). After the 30th week, a
prominent venous plexus lies between the decidua basalis and
myometrium and helps develop the cleavage plane needed for
placental separation after delivery.
Both inlow and outlow are curtailed during uterine con­
tractions. BIeker and associates ( 1 975) used serial sonography
during normal labor and found that placental length, thickness,
and surface area grew during contractions. They attributed this
to distention of the intervillous space by impairment of venous
outlow compared with arterial inlow. During contractions,
therefore, a somewhat larger volume of blood is available for
exchange even though the rate of low is decreased. Similarly,
Doppler velocimetry has shown that diastolic low veloci ty in
spiral arteries is diminished during uterine contractions. Thus,
principal factors regulating intervillous space blood low are
arterial blood pressure, intrauterine pressure, uterine contrac­
tion pattern, and factors that act specifically on arterial walls.
• Breas in the Placental "Barrier"
he placenta does not maintain absolute integrity of the fetal
and maternal circulations. here are numerous examples of
Materna l C i rcu lation
Mechanisms of placental blood
low must allow blood to leave
maternal circulation; flow into
an amorphous space lined by
syncytiotrophoblast, rather than
endothelium; and return through
maternal veins without produc­
ing arteriovenous-like shunts that
would prevent maternal blood from
remaining in contact with villi long
enough for adequate exchange. For
this, maternal blood enters through
the basal plate and is driven high
up toward the chorionic plate by
arterial pressure before laterally dis­
persing (Fig. 5- 1 5) . After bathing
the external microvillous surface
of chorionic villi, maternal blood
drains back through venous ori­
ices in the basal plate and enters
uterine veins. Thus, maternal blood
traverses the placenta randomly
without preformed channels. The
previously described trophoblast
invasion of the spiral arteries creates
U mbilical ­
vein
\
U mbilical artery
U mbil ical cord
I.
Chorionic plate
Chorionic -­
villus
Basal
plate
Spiral
artery
Decidual septum
FIGURE 5-1 5 Schematic d rawing of a section through a fu l l-term placenta. Materna l blood flows
i nto the intervi llous spaces in fu n nel-shaped spurts. Excha nges occur with feta l b lood as maternal
blood flows a round the vi l l i . I nfiowi ng a rterial blood pushes venous blood i nto the endometrial
vei ns, which a re scattered over the entire su rface of the decidua basal is. Note a lso that the u m b ilical
a rteries ca rry deoxygenated feta l blood to the placenta and that the umbilica l vei n ca rries oxygen­
ated blood to the fetus. Placenta l lobes a re separated from each other by placental (decidual) septa.
I m p l a ntatio n a n d Placenta l Deve l o p ment
traicking cells between mother and fetus in both directions.
This situation is best exempliied clinically by erythrocyte
D-antigen alloimmunization (Chap. 1 5, p. 30 1 ) . Fetal cell
admixtures likely are small in most cases, although rarely the
fetus exsanguinates into the maternal circulation.
Fetal cells can also engraft in the mother during pregnancy
and can be identiied decades later. Fetal lymphocytes, CD34+
mesenchymal stem cells, and endothelial colony-forming cells
all reside in maternal blood, bone marrow, or uterine vascula­
ture (Nguyen, 2006; Piper, 2007; Sipos, 20 1 3) . Termed micro­
chimerism, such residual stem cells have been implicated in the
disparate female:male ratio of autoimmune disorders (Greer,
20 1 1 ; Stevens, 2006) . As discussed in Chapter 59 (p. 1 1 39) ,
they are associated with the pathogenesis of lymphocytic thy­
roiditis, scleroderma, and systemic lupus erythematosus.
• Fetal-Maternal Interface
Survival of the semi allogenic fetal graft requires complex interac­
tions between fetal trophoblasts and maternal decidual immune
cells. The fetal-maternal interface is not immunologically inert.
Rather, it is an active hub of interactions that allows implanta­
tion and appropriate placental development and ensures immu­
no tolerance of the fetus. Despite this, a functional immune
system must be maintained to protect the mother.
I m m u nogen ic ity of the Trophobl a sts
Trophoblastic cells are the only fetus-derived cells in direct
contact with maternal tissues and blood. Fetal syncytiotropho­
blast synthesizes and secretes numerous factors that regulate the
immune responses of maternal cells both at the implantation
site and systemically.
Human leukocyte antigens (HLAs) are the human analogue
of the major histocompatibility complex (MHC) (Hunt, 1 992) .
There are 1 7 HLA class I genes, including three classic genes,
HLA-A, -B, and -C, that encode the major class I (class Ia)
transplantation antigens. Three other class I genes, designated
HLA-E, -F, and -G, encode class Ib HLA antigens. MHC class
I and II antigens are absent from villous trophoblasts, which
appear to be immunologically inert at all gestational stages
(Weetman, 1 999) . Invasive extravillous cytotrophoblasts do
express MHC class I molecules. Thus, the ability of these cells
to bypass transplantation rejection is the focus of considerable
study.
Mofett-King (2002) reasoned that normal implantation
depends on controlled trophoblastic invasion of maternal
decidua and spiral arteries. Such invasion must proceed far
enough to provide for normal fetal growth and development,
but a mechanism must regulate invasion depth. She suggests
that dNK cells combined with unique expression of three spe­
ciic HLA class I genes in extravillous cytotrophoblasts act in
concert to permit and subsequently limit trophoblast invasion.
Class I antigens in extravillous cytotrophoblasts are
accounted for by the expression of classic HLA-C and nonclas­
sic class Ib molecules of HLA-E and HLA-G. HLA-G anti­
gen is expressed only in humans, with expression restricted to
extravillous cytotrophoblasts contiguous with maternal tissues.
Embryos used for in vitro fertilization do not implant if they
do not express a soluble HLA-G isoform (Fuzzi, 2002) . hus,
HLA-G may be immunologically permissive of the maternal­
fetal antigen mismatch (LeBouteiller, 1 999) . HLA-G has a pro­
posed role in protecting extravillous trophoblasts from immune
rejection via modulation of dNK functions (Apps, 201 1 ; Raja­
gopalan, 20 1 2) . Last, Goldman-Wohl and associates (2000)
have provided evidence for abnormal HA-G expression in
extravillous trophoblasts from women with preeclampsia.
Dec i d u a l I m m u ne Cel ls
Natural killer cells are the predominant population of leuko­
cytes present in midluteal phase endometrium and in decidua
throughout the fi r st trimester Oohnson, 1 999). By term,
however, relatively few dNK cells are present in decidua. In
first-trimester decidua, dNK cells lie close to extravillous tro­
phoblasts, and there they purportedly serve to regulate inva­
sion. These dNKs have a distinct phenotype characterized by a
high surface density of CD56 or neural cell adhesion molecules
(Manaster, 2008; Mofett-King, 2002) . Their infiltration is
increased by progesterone and by stromal cell production of
IL- 1 5 and decidual prolactin (Dunn, 2002; Gubbay, 2002) .
Although dNK cells have the capacity for cytotoxicity, they are
not cytotoxic toward fetal trophoblasts. Their cytotoxic poten­
tial is prevented by molecular cues from decidual macrophages.
In addition, the expression of specific HLA molecules protects
against dNK killing. Also, dNK cells function to restrict tro­
phoblast invasiveness to protect the mother.
Of other cell types, decidual macrophages are distinct from
proinflammatory M 1 or antiinlammatory M2 macrophages.
Decidual macrophages express the complement receptor
CO l I c at high or low levels: CD 1 1 cH I and CD 1 1 cLO. These
cells function to regulate adaptive T cell responses; control
dNK diferentiation, activation, and cytotoxicity; and produce
antiinlammatory cytokines such as I L- 1 0 to ensure fetal toler­
ance and inhibition of harmful immune responses.
Dendritic cells are cells that present antigens to T cells. hey
play an important role in the development of a receptive endo­
metrium for implantation.
Maternal T cels, as part of the adaptive immune response,
increase in number and function after encounter with a speciic
antigen. These cells subsequently retain the ability to respond
rapidly in a subsequent encounter with the same antigen. Spe­
cific populations of Treg cells persist and can protect against
aberrant immune responses. During pregnancy, there is a
systemic expansion of maternal Treg cell populations. These
cells are FOXP3 + cells with defined fetal speciicity. They are
immunosuppressive and play a role in fetal tolerance.
AMNION
At term, the amnion is a tough and tenacious but pliable mem­
brane. his innermost avascular fetal membrane is contiguous
with amnionic fluid and plays a role of incredible importance
in human pregnancy. he amnion provides almost all tensile
strength of the fetal membranes. Thus, its resilience to rupture
is vitally important to successful pregnancy outcome. Indeed,
preterm rupture of fetal membranes is a major cause of preterm
delivery (Chap. 42, p. 8 1 9) .
95
96
P l acentation, E m bryog enesis, a n d Feta l Development
diamnionic-dichorionic twin placentas, amnions are separated
by fused chorion laeve.
Amnionic luid ills this amnionic sac. Until about 34
weeks' gestation, the normally clear fluid increases in volume
as pregnancy progresses. Mter this, the volume declines. At
term, amnionic luid averages 1 000 mL, although this may vay
widely in normal and especially abnormal conditions. The ori­
gin, composition, circulation, and function of amnionic luid
are discussed further in Chapter 1 1 (p. 225).
• Amnion Cell Histogenesis
FIGURE 5-1 6 Photomicrog raph of feta l membra nes. F rom left to
rig ht: AE = a m n ion epithe l i u m; AM a m n ion mesenchyme; S
zon a spong i osa; eM chorionic mesenchyme; TR = trophoblast;
0 = decid ua. (U sed with permission from Dr. J udith R. Head.)
=
=
=
Bourne ( 1 962) described five separate amnion layers. he
inner surface, which is bathed by amnionic luid, is an unin­
terrupted, single layer of cuboidal epithelium (Fig. 5- 1 6) . his
epithelium is attached irmly to a distinct basement membrane
that is connected to an acellular compact layer composed pri­
marily of interstitial collagens. On the outer side of the com­
pact layer, there is a row of ibroblast-like mesenchymal cells,
which are widely dispersed at term. here also are a few fetal
macrophages in the amnion. he outermost amnion layer is the
relatively acellular zona spongiosa, which is contiguous with the
second fetal membrane, the chorion laeve. he human amnion
lacks smooth muscle cells, nerves, lymphatics, and importantly,
blood vessels.
• Amnion Development
Early during implantation, a space develops between the
embryonic cell mass and adjacent trophoblastic cells (see
Fig. 5-9) . Small cells that line this inner surface of tropho­
blasts have been called amniogenic cells-precursors of amni­
onic epithelium. The amnion is irst identiiable on the 7th
or 8th day of embryo development. It is initially a minute
vesicle, which then develops into a small sac that covers the
dorsal embryo surface. As the amnion enlarges, it gradually
engulfs the growing embryo, which prolapses into its cavity
(Benirschke, 20 1 2) .
Distention o f the amnionic sac eventually brings i t into con­
tact with the interior surface of the chorion laeve. Apposition of
the chorion laeve and amnion near the end of the irst trimes­
ter then causes an obliteration of the extraembryonic coelom.
he amnion and chorion laeve, although slightly adhered, are
never intimately connected and can be separated easily. Placen­
tal amnion covers the placental surface and thereby is in con­
tact with the adventitial surface of chorionic vessels. Umbilical
amnion covers the umbilical cord. With diamnionic-mono­
chorionic placentas, there is no intervening tissue between
the fused amnions. In the conjoined portion of membranes of
Epithelial cells of the amnion derive from fetal ectoderm of
the embryonic disc. hey do not arise by delamination from
trophoblasts. his is an important consideration from both
embryological and functional perspectives. For example, HLA
class I gene expression in amnion is more akin to that in emby­
onic cells than to that in trophoblasts.
he ibroblast-like mesenchymal cell layer of the amnion
is likely derived from embryonic mesoderm. Early in human
embryogenesis, the amnionic mesenchymal cells lie immedi­
ately adjacent to the basal surface of the amnion epithelium. At
this time, the amnion surface is a two-cell layer with approxi­
mately equal numbers of epithelial and mesenchymal cells.
Simultaneously with growth and development, interstitial col­
lagens are deposited between these two cell layers. his marks
formation of the amnion compact layer, which separates the
two layers of amnion cells.
As the amnionic sac expands, the compactness of the mes­
enchymal cells is progressively reduced, and they become
sparsely distributed. Early in pregnancy, amnionic epithelium
replicates at a rate appreciably faster than mesenchymal cells.
At term, these cells form a continuous uninterrupted epithe­
lium on the fetal amnionic surface. Conversely, mesenchymal
cells are widely dispersed, being connected by a ine lattice
network of extracellular matrix with the appearance of long
slender ibrils.
Am n ion Epith e l i a l Ce l l s
h e apical surface o f the amnionic epithelium i s replete with
highly developed microvilli. This structure relects its function
as a major site of transfer between amnionic luid and amnion.
This epithelium is metabolically active, and its cells synthesize
tissue inhibitor of MMP- l , prostaglandin E2 (PGE2) , and fetal
ibronectin (FN) (Rowe, 1 997) . Although epithelia produce
FN, recent studies suggest that ibronectin functions in the
underlying mesenchymal cells. Here, FN promotes synthesis
of MMPs that break down the strength-bearing collagens and
enhance prostaglandin synthesis to prompt uterine contractions
(Mogami, 20 1 3) . This pathway is upregulated in premature rup­
ture of membranes induced by thrombin or infection-induced
release of FN (Chigusa, 20 1 6; Mogami, 20 1 4) .
Epithelial cells may respond t o signals derived from the fetus
or the mother, and they are responsive to various endocrine or
paracrine modulators. Examples include oxytocin and vasopres­
sin, both of which increase PGE2 production in vitro (Moore,
1 988) . They may also produce cytokines such as IL-8 during
labor initiation (Elliott, 200 1 ) .
I m pla ntation a nd Place n ta l Deve l o p m ent
Amnionic epithelium also synthesizes vasoactive pep tides,
including endothelin and parathyroid hormone-related protein
(Economos, 1 992; Germain, 1 992) . he tissue produces brain
natriuretic peptide (BNP) and corticotropin-releasing hormone
(CRH), which are peptides that invoke smooth-muscle relax­
ation (Riley, 1 99 1 ; Warren, 1 995) . BNP production is posi­
tively regulated by mechanical stretch in fetal membranes and is
proposed to function in uterine quiescence. Epidermal growth
factor, a negative regulator of BNP, is up regulated in the mem­
branes at term and leads to a decline in BNP-regulated uterine
quiescence (Carvaj al, 20 1 3) . It seems reasonable that vasoac­
tive peptides produced in amnion gain access to the adventitial
surface of chorionic vessels. hus, the amnion may be involved
in modulating chorionic vessel tone and blood low. Amnion­
derived vasoactive peptides function in both maternal and fetal
tissues in diverse physiological processes. After their secretion,
these bioactive agents enter amnionic luid and thereby are
available to the fetus by swallowing and inhalation.
Am ni o n M esenchym a l Cel l s
Mesenchymal cells o f the amnionic ibroblast layer are respon­
sible for other major functions. Synthesis of interstitial col­
lagens that compose the compact layer of the amnion-the
major source of its tensile strength-takes place in mesenchy­
mal cells (Casey, 1 996) . At term the generation of cortisol by
l 1 �-hydroxysteroid dehydrogenase may contribute to mem­
brane rupture via reduction of collagen abundance (Mi, 20 1 7) .
Mesenchymal cells also synthesize cytokines that include IL-6,
IL-8, and MCP- I . Cytokine synthesis rises in response to
bacterial toxins and IL- 1 . his functional capacity of amnion
mesenchymal cells is an important consideration in amnionic
fluid study of labor-associated accumulation of inlammatory
mediators (Garcia-Velasco, 1 999) . Finally, mesenchymal cells
may be a greater source of PGE2 than epithelial cells, especially
in the case of premature membrane rupture (Mogami, 20 1 3;
Whittle, 2000) .
• Tensile Strength
During tests of tensile strength, the decidua and then the cho­
rion laeve give way long before the amnion ruptures. Indeed,
the membranes are elastic and can expand to twice normal
size during pregnancy (Benirschke, 20 1 2) . The amnion tensile
strength resides almost exclusively in the compact layer, which
is composed of cross-linked interstitial collagens I and III and
lesser amounts of collagens V and VI.
Collagens are the primary macromolecules of most connec­
tive tissues. Collagen I is the major interstitial collagen in tis­
sues characterized by great tensile strength, such as bone and
tendon. In other tissues, collagen III is believed to contribute to
tissue integrity and provides both tissue extensibility and tensile
strength. For example, the ratio of collagen III to collagen I in
the walls of a number of highly extensible tissues-amnionic sac,
blood vessels, urinary bladder, bile ducts, intestine, and gravid
uterus-is greater than that in nonelastic tissues a efrey, 1 99 1 ) .
Amnion tensile strength is regulated in part by fibrillar
collagen assembly. his process is influenced by the interac­
tion fibrils with proteoglycans such as decorin and biglycan
(Chap. 2 1 , p. 409). Reduction of these proteoglycans is
reported to perturb fetal membrane function (Horgan, 20 1 4;
Wu, 20 1 4) . Fetal membranes overlying the cervix have a
regional shift in gene expression and lymphocyte activation that
set in motion an inflammatory cascade (Marcellin, 20 1 7) . his
change may contribute to tissue remodeling and loss of tensile
strength in the amnion (Moore, 2009) .
• Metabolic Functions
The amnion is metabolically active, is involved in solute and
water transport for amnionic fluid homeostasis, and produces
an impressive array of bioactive compounds. The amnion is
responsive both acutely and chronically to mechanical stretch,
which alters amnionic gene expression (Carvajal, 20 1 3;
Nemeth, 2000) . This in turn may trigger both autocrine and
paracrine responses that include production of MMPs, IL-8,
and collagenase (Bryant-Greenwood, 1 998; Mogami, 20 1 3) .
Such factors may modulate changes i n membrane properties
during labor.
UMBI LICAL CORD
he yolk sac and the umbilical vesicle into which it develops are
prominent early in pregnancy. At irst, the embryo is a lattened
disc interposed between amnion and yolk sac (see Fig. 5-9) . Its
dorsal surface grows faster than the ventral surface, in associa­
tion with the elongation of its neural tube. Thus, the embryo
bulges into the amnionic sac, and the dorsal part of the yolk
sac is incorporated into the embryo body to form the gut. The
allantois projects into the base of the body stalk from the cau­
dal wall of the yolk sac and later, from the anterior wall of the
hindgut.
As pregnancy advances, the yolk sac becomes smaller and
its pedicle relatively longer. By the middle of the third month,
the expanding amnion obliterates the extraembryonic coelom,
fuses with the chorion laeve, and covers the bulging placental
disc and the lateral surface of the body stalk. The latter is then
called the umbilical cord-or funis. A more detailed descrip­
tion of this cord and potential abnormalities is found in Chap­
ter 6 (p. 1 1 7) .
h e cord at term normally has two arteries and one vein
(Fig. 5- 1 7) . The right umbilical vein usually disappears early
during fetal development, leaving only the original left vein.
The umbilical cord extends from the fetal umbilicus to the
fetal surface of the placenta, that is, the chorionic plate. B lood
flows from the umbilical vein toward the fetus. Blood then
takes a path of least resistance via two routes within the fetus.
One is the ductus venosus, which empties directly into the infe­
rior vena cava (Fig. 7-9, p. 1 30). The other route consists of
numerous smaller openings into the hepatic circulation. Blood
from the liver flows into the inferior vena cava via the hepatic
vein. Resistance in the ductus venosus is controlled by a sphinc­
ter that is situated at the origin of the ductus at the umbilical
recess and is innervated by a vagus nerve branch.
Blood exits the fetus via the two umbilical arteries. These
are anterior branches of the internal iliac artery and become
obliterated after birth to form the medial umbilical ligaments.
97
98
P l a ce ntation, E m b ryogenesis, a n d Feta l Deve l op m e nt
physiological adaptations of pregnant women to the unique
endocrine milieu, and this is discussed throughout Chapter 4
(p. 49) .
• Human Chorionic Gonadotropin
Biosynthesis
FIGURE 5-1 7 Cross-section of u m bi l ica l cord. The large u m bi l ica l
vei n ca rries oxygenated blood to the fetus (right). To its left a re the
two s m a l ler u m bil ica l a rteries, ca rryi n g deoxygenated b lood fro m
the fetus to the placenta. (Used with perm ission from Dr. M a n d o l i n
S. Ziadie.)
PLACENTAL HORMON ES
The production of steroid and protein hormones by human
trophoblasts is greater in amount and diversity than that of
any single endocrine tissue in all of mammalian physiology.
A compendium of average production rates for various steroid
hormones in nonpregnant and in near-term pregnant women
is given in Table 5- 1 . It is apparent that alterations in steroid
hormone production that accompany normal human preg­
nancy are incredible. he human placenta also synthesizes an
enormous amount of protein and peptide hormones, summa­
rized in Table 5-2 . Another remarkable feature is the successful
TABLE 5-1 . Ste roid Prod uction Rates in Non preg n a nt
and Nea r-Term Preg n a nt Women
Steroida
Estrad iol- 1 7�
Estr i o l
P rogesterone
Al d oste rone
Deoxyc o rti costero ne
Cortisol
Production Rates (mg/24 h r)
Nonpreg nant
Pregnant
0. 1 -0.6
0.02-0. 1
0. 1 -40
0.05-0. 1
0.05-0.5
1 0-30
1 5-20
50- 1 50
250-600
0.2 5 0-0.600
1 -1 2
1 0-20
a Estrogens a n d p rogesterone a re p rod uced by placenta.
Aldosterone is prod uced by the maternal a d renal in response
to the sti m u l us of ang iotensin I I. Deoxycorticosterone is p ro­
d uced i n extrag landular tissue sites by way of the 2 1 -hyd rox­
ylation of plasma progesterone. Cortisol p rod uction d u r i ng
p reg nancy is not increased, even though the blood levels
a re elevated beca use of decreased clearance ca u sed by
i ncreased cortisol-bi nding g lobu l i n.
Chorionic gonadotropin is a glycoprotein with biological activ­
ity similar to that of LH, and both act via the same LH-hCG
receptor. hCG has with a molecular weight of 36,000 to 40,000
Da and has the highest carbohydrate content of any human
hormone-30 percent. The carbohydrate component, and espe­
cially the terminal sialic acid, protects the molecule from catabo­
lism. As a result, the 36-hour plasma half-life of intact hCG is
much longer than the 2 hours for LH. he hCG molecule is
composed of two dissimilar subunits termed . and � subunits.
hese are noncovalently linked and are held together by elec­
trostatic and hydrophobic forces. Isolated subunits are unable
to bind the LH-hCG receptor and thus lack biological activity.
hCG is produced almost exclusively in the placenta, but low
levels are synthesized in the fetal kidney. Other fetal tissues pro­
duce either the �-subunit or intact hCG molecule (McGregor,
1 98 1 , 1 983) .
The hCG hormone is structurally related to three other
glycoprotein hormones-LH, FSH, and TSH. All four glyco­
proteins share a common a-subunit. However, each of their
3-subunits, although sharing certain similarities, is character­
ized by a distinctly diferent amino acid sequence.
Synthesis of the .- and 3-chains of hCG is regulated sep­
arately. A single gene located on chromosome 6 encodes the
a-subunit. Seven genes on chromosome 1 9 encode for the
� -hCG-3-LH family of subunits. Six genes code for 3-hCG
and one for 3-LH (Miller-Lindholm, 1 997) . Both subunits
are synthesized as larger precursors, which are then cleaved
by endopeptidases. Intact hCG is then assembled and rapidly
released by secretory granule exocytosis (Morrish, 1 987) . There
are multiple forms of hCG in maternal plasma and urine that
vary enormously in bioactivity and immunoreactivity. Some
result from enzymatic degradation, and others from modifica­
tions during molecular synthesis and processing.
Before 5 weeks, hCG is expressed both in the syncytiotro­
phoblast and in cytotrophoblasts (Mamo, 1 992) . Later, in the
irst trimester when maternal serum levels peak, hCG is pro­
duced almost solely in the syncytiotrophoblast (Beck, 1 986;
Kurman, 1 984) . At this time, mRNA concentrations of both
.- and 3-subunits in the syncytiotrophoblast are greater than
at term (Hoshina, 1 982) . This may be an important consider­
ation when hCG is used as a screening procedure to identiy
abnormal fetuses.
Circulating free levels of 3-subunit are low to undetectable
throughout pregnancy. In part, this is the result of its rate-lim­
iting synthesis. Free a-subunits that do not combine with the
3-subunit are found in placental tissue and maternal plasma. Lev­
els of the a-subunit rise gradually and steadily until they plateau
at approximately 36 weeks' gestation. At this time, they account
for 30 to 50 percent of hormone (Cole, 1 997) . Thus, .-hCG
secretion roughly corresponds to placental mass, whereas secre­
tion of complete hCG molecules is maximal at 8 to 1 0 weeks.
I m p l a ntat i o n a n d Placental Develo p m ent
TABLE 5-2. Protei n Hormones P rod uced by the Human Pl acenta
Prim a ry Non-placental
Site of Expression
Hormone
Shares Structura l or
Fu nction Simila rity
Fu nctions
H u m a n chori o n i c
g o n a d ot ropin (hCG)
LH, FSH, TS H
Ma i nta i n s corpus l ute u m fu ncti on
Reg u lates fetal testis testosterone secretion
Sti m u lates maternal thyroid
P l acenta l lactoge n (PL)
G H , p ro l acti n
A i d s mate r n a l a d a ptation t o feta l e n e rgy
req u i re m ents
Ad renocorticotro p i n (ACTH)
Hypoth a l a m u s
Corticotro p i n-releasing
hormone (CRH)
Hypot h a la m u s
Relaxes smooth-muscle; i n itiates partu rition ?
P romotes feta l a n d maternal
g l u cocorticoid prod uction
Gonadotropi n-re lea s i n g
h o r m o n e (G n RH)
Hypoth a l a m u s
Reg u l ates t ro p h o b l ast hCG prod u ction
Thyrotro p i n (TRH)
Hypotha l a m u s
U n known
G rowth horm on e- relea s i n g
hormone (G H RH)
Hypotha l a m u s
U n known
G rowt h hormone va riant
( h G H -V)
N e u ro peptide Y
GH va ria nt not fou nd
i n pituita ry
B ra i n
Potenti a l ly med iates preg na ncy i n s u l i n
resi sta nce
Potential reg u lates CRH release by
t rop h o b l a sts
Parathyro i d -relea s i n g
prote i n (PTH-rp)
Reg u lates t ra n sfer of ca l c i u m a n d
o t h e r solutes; reg u l ates feta l m i neral
h o m eosta s i s
I nh i bi n
Ova ry/testis
Potent i a l l y i n h i b its FSH- med iated
ovu lation; reg u l ates hCG synthesis
Activin
Ova ry/testis
Reg u l ates placenta l G n RH synthesis
GH
=
g rowth hormone; FSH
=
fol l icle-sti m u lati n g hormone; LH
Concentrati ons in Seru m a n d U ri ne
The combined hCG molecule is detectable in plasma of preg­
nant women 7 to 9 days after the midcycle surge of LH that
precedes ovulation. hus, hCG likely enters maternal blood at
the time of blastocyst implantation. Plasma levels rise rapidly,
doubling every 2 days in the first trimester (Fig. 5- 1 8) . Appre­
ciable fluctuations in levels for a given patient are observed on
the same day.
Intact hCG circulates as multiple highly related isoforms
with variable cross-reactivity between commercial assays. hus,
calculated serum hCG levels can vary considerably among the
more than a hundred available assays. his emphasizes the
need to use the same assay type when clinically measuring
serial hCG levels. Peak maternal plasma levels reach approxi­
mately 50,000 to 1 00,000 mIU/mL between the 60th and
80th days after menses. At 10 to 1 2 weeks' gestation, plasma
levels begin to decline, and a nadir is reached by approximately
1 6 weeks. Plasma levels are maintained at this lower level for
the remainder of pregnancy.
The pattern of hCG appearance in fetal blood is similar to
that in the mother. Fetal plasma levels, however, are only about
3 percent of those in maternal plasma. Amnionic fl u id hCG
concentration early in pregnancy is similar to that in mater­
nal plasma. As pregnancy progresses, hCG concentration in
=
l utei n iz i n g hormone; TS H
=
thyroid-st i m u lat i ng h or m o n e.
amnionic fluid declines, and near term the levels are approxi­
mately 20 percent of those in maternal plasma.
Maternal urine contains the same variety of hCG degrada­
tion products as maternal plasma. The principal urinary form
is the terminal product of hCG degradation, namely, the
1 40
1 20
1\
I I
I
I
I
I
I
I
I
I
I
I
,
I
I
I
I
I
I
\
I
\
,
I
_ 1 00
E
80
3
) 60
>
c
40
,
20
0
I
� � hCG
J
0
I
I
,,
10
"
h P L �/
,,
500
,
400
,
,,
,
"
"7..- ,
,
,,
,
,,
E
I
30
20
Weeks' gestation
J
300 �
0
I
,
8
7
.
200 £
1 00
40
:
)
6
53
E
4,
:t
3.
1
2
0
FIGURE 5-1 8 Disti nct profi les for the concentrations of h u m a n
chorionic gonadotropin (hCG), h u m a n placental lactogen ( h P L),
and corticotropin-releasing hormone (CRH) i n seru m of wome n
throug hout normal preg nancy.
c
99
1 00
P l a centation, E m b ryogenesis, a n d Feta l Deve lopment
�-core fragment. Concentrations of this fragment follow the
same general pattern as that in maternal plasma, peaking at
approximately 1 0 weeks' gestation. Importantly, the so-called
�-subunit antibody used in most pregnancy tests reacts with
both intact hCG-the major form in the plasma, and with
fragments of hCG-the major forms found in urine.
hCG Reg u l ation
Placental gonadotropin-releasing hormone (GnRH) is likely
involved in the regulation of hCG formation. Both GnRH and
its receptor are expressed by cytotrophoblasts and by the syn­
cytiotrophoblast (Wolfahrt, 1 998). GnRH administration ele­
vates circulating hCG levels, and cultured trophoblasts respond
to GnRH treatment and raise hCG secretion (Iwashita, 1 993;
Siler-Khodr, 1 98 1 ) . Pituitary GnRH production also is regu­
lated by inhibin and activin. In cultured placental cells, activin
stimulates and inhibin inhibits GnRH and hCG production
(Petraglia, 1 989; Steele, 1 993) .
Renal clearance of hCG accounts for 30 percent of its meta­
bolic clearance. he remainder is likely cleared by metabolism
in the liver (Wehmann, 1 980) . Clearances of�- and .-subunits
are approximately 1 0- and 30-fold, respectively, greater than
that of intact hCG. In pregnancies complicated by chronic
renal disease, hCG clearance can be markedly decreased.
Biologica l Fu nctions
Both hCG subunits are required for binding to the LH-hCG
receptor in the corpus luteun and the fetal testis. LH-hCG
receptors are present in various other tissues, but their roles
there are less defined.
he best-known biological function of hCG is the so-called
rescue and maintenance of corpus luteum function-that is,
continued progesterone production. This is only an incomplete
explanation for the physiological function of hCG in preg­
nancy. For example, maximum plasma hCG concentrations are
attained well after hCG-stimulated corpus luteum secretion of
progesterone has ceased. Speciically, luteal progesterone syn­
thesis begins to decline at about 6 weeks despite continued and
increasing hCG production.
A second hCG role is stimulation of fetal testicular testos­
terone secretion. This is maximum approximately when hCG
levels peak. hus, at a critical time in male sexual diferentia­
tion, hCG enters fetal plasma from the syncytiotrophoblast. In
the fetus, it acts as an LH surrogate to stimulate Leydig cell rep­
lication and testosterone synthesis to promote male sexual dif­
ferentiation (Chap. 3, p. 35). Before approximately 1 1 0 days,
there is no vascularization of the fetal anterior pituitary from
the hypothalamus. Thus, pituitary LH secretion is minimal,
and hCG acts as LH before this time. hereafter, as hCG levels
fall, pituitary LH maintains modest testicular stimulation.
The maternal thyroid gland is also stimulated by large quan­
tities of hCG. In some women with gestational trophoblastic
disease, biochemical and clinical evidence of hyperthyroidism
sometimes develops (Chap. 20, p. 39 1 ) . This once was attrib­
uted to formation of chorionic thyrotropins by neoplastic
trophoblasts. It was subsequently shown, however, that some
forms ofhCG bind to TSH receptors on thyrocytes (Hershman,
1 999) . And, treatment of men with exogenous hCG increases
thyroid activity. The thyroid-stimulatory activity in plasma of
irst-trimester pregnant women varies appreciably from sample
to sample. Modiications of hCG oligosaccharides likely are
important in the capacity of hCG to stimulate thyroid func­
tion. For example, acidic isoforms stimulate thyroid activity,
and some more basic isoforms stimulate iodine uptake (Kraiem,
1 994; Tsuruta, 1 995; Yoshimura, 1 994) . Finally, the LH-hCG
receptor is expressed by thyrocytes, which suggests that hCG
stimulates thyroid activity via the LH-hCG receptor as well as
by the TSH receptor (Tomer, 1 992) .
Other hCG functions include promotion of relaxin secre­
tion by the corpus luteum (Duy, 1 996) . LH-hCG receptors
are found in myometrium and in uterine vascular tissue. It
has been hypothesized that hCG may promote uterine vascu­
lar vasodilatation and myometrial smooth muscle relaxation
(Kurtzman, 200 1 ) . Chorionic gonadotropin also regulates
expansion of dNK cell numbers during early stages of placen­
tation, thus ensuring appropriate establishment of pregnancy
(Kane, 2009) .
A b norma l ly H i g h or Low Level s
here are several clinical circumstances i n which substantively
higher maternal plasma hCG levels are found. Some examples
are multifetal pregnancy, erythroblastosis fetalis associated with
fetal hemolytic anemia, and gestational trophoblastic disease.
Relatively higher hCG levels may be found in women carry­
ing a fetus with Down syndrome. This observation is used in
biochemical screening tests (Chap. 1 4, p. 28 1 ) . The reason for
the elevation is not clear, but reduced placental maturity has
been speculated. Various malignant tumors also produce hCG,
sometimes in large amounts-especially trophoblastic neoplasms
(Chaps. 9, p. 1 59 and 20, p. 39 1 ) .
Relatively lower hCG plasma levels are found i n women with
early pregnancy wastage, including ectopic pregnancy (Chap.
1 9, p. 373) . hCG is produced in very small amounts in normal
tissues of men and nonpregnant women, perhaps primarily in
the anterior pituitary gland. Nonetheless, the detection of hCG
in blood or urine almost always indicates pregnancy (Chap. 9,
p. 1 58).
• Human Placental Lactogen
B iosynthesi s
This is a single, nonglycosylated polypeptide chain with a molec­
ular weight of 22,279 Da. The sequences of hPL and of human
growth hormone (hGH) are strikingly similar, with 96-percent
homology. Also, hPL is structurally similar to human prolac­
tin (hPRL) , with a 67-percent amino acid sequence similarity.
Because of these similarities, it was called human placental lac­
togen or chorionic growth hormone. Currently, human placen­
tal lactogen is used by most.
here are ive genes in the growth hormone-placental lac­
togen gene cluster that are linked and located on chromosome
1 7. hPL is concentrated in syncytiotrophoblast, but similar
to hCG, hPL is demonstrated in cytotrophoblasts before 6
weeks (Grumbach, 1 964; Maruo, 1 992) . Within 5 to 1 0 days
after conception, hPL is demonstrable in the placenta and can
be detected in maternal serum as early as 3 weeks. Levels of
I m pl a ntation and Placenta l Deve l o pment
mRNA for hPL in syncytiotrophoblast remain relatively con­
stant throughout pregnancy. his inding supports the idea that
the hPL secretion rate is proportional to placental mass. Levels
rise steadily until 34 to 36 weeks' gestation. The hPL produc­
tion rate near term-approximately 1 g/d-is by far the great­
est of aRY known hormone in humans. The hal-life of hPL in
maternal plasma is between 1 0 and 30 minutes (Walker, 1 99 1 ) .
I n late pregnancy, maternal serum concentrations reach levels
of 5 to 1 5 �g/mL (see Fig. 5- 1 8) .
Very little hPL i s detected i n fetal blood o r i n the urine of
the mother or newborn. Amnionic fluid levels are somewhat
lower than in maternal plasma. hPL is secreted primarily into
the maternal circulation, with only very small amounts in cord
blood. hus, its role in pregnancy is believed to be mediated
through actions in maternal rather than in fetal tissues. None­
theless, interest continues for the possibility that hPL serves
select functions in fetal growth.
Meta bol ic Actions
hPL has putative actions in several important metabolic pro­
cesses. First, hPL promotes maternal lipolysis with increased
circulating free fatty acid levels. This provides an energy
source for maternal metabolism and fetal nutrition. In vitro
studies suggest that hPL inhibits leptin secretion by term syn­
cytiotrophoblast (Coya, 2005) . Prolonged maternal starvation
in the irst half of pregnancy leads to higher hPL plasma con­
centrations.
Second, hPL may aid maternal adaptation to fetal energy
requirements. For example, increased maternal insulin resis­
tance ensures nutrient flow to the fetus. It also favors protein
synthesis and provides a readily available amino acid source to
the fetus. To counterbalance the greater insulin resistance and
prevent maternal hyperglycemia, maternal insulin levels are
increased. Both hPL and prolactin signal through the prolactin
receptor to increase maternal beta cell proliferation to augment
insulin secretion (Georgia, 20 1 0) . In animals, prolactin and
hPL upregulate serotonin synthesis, which increases beta cell
proliferation (Kim, 20 1 0) . Short-term changes in plasma glu­
cose or insulin, however, have relatively little efect on plasma
hPL levels. In vitro studies of syncytiotrophoblast suggest that
hPL synthesis is stimulated by insulin and insulin-like growth
factor- 1 and inhibited by PGE2 and PGF2: (Bhaumick, 1 987;
Genbacev, 1 977) .
Last, hPL is a potent angiogenic hormone. It may serve an
important function in fetal vasculature formation (Corbacho,
2002) .
• Other Placental Protein Hormones
he placenta has a remarkable capacity to synthesize numer­
ous peptide hormones, including some that are analogous or
related to hypothalamic and pituitary hormones. In contrast
to their counterparts, some of these placental peptide/protein
hormones are not subject to feedback inhibition.
H ypotha l a m ic-Like R e l ea s i ng Hormones
he known hypothalamic-releasing or -inhibiting hormones
include GnRH, CRH , thyrotropin-releasing hormone (TRH) ,
growth hormone-releasing hormone, and somatostatin. For
each, there is an analogous hormone produced in the human
placenta (Petraglia, 1 992; Siler-Khodr, 1 988) .
GnH in the placenta shows its highest expression in the
first trimester (Siler-Khodr, 1 978, 1 988). Interestingly, it is
found in cytotrophoblasts, but not syncytiotrophoblast. Pla­
centa-derived GnRH functions to regulate trophoblast hCG
production and extravillous trophoblast invasion via regulation
ofMMP-2 and MMP-9 (Peng, 20 1 6) . Placenta-derived G nRH
is also the likely cause of elevated maternal GnRH levels in
pregnancy (Siler-Khodr, 1 984).
CH is a member of a larger family of CRH-related pep­
tides that includes CRH and urocortins (Dautzenberg, 2 002) .
Maternal serum CRH levels increase from 5 to 1 0 pmollL in
the nonpregnant woman to approximately 1 00 pmollL in the
early third trimester of pregnancy and to almost 500 pmollL
abruptly during the last 5 to 6 weeks (see Fig. 5- 1 8) . Urocortin
also is produced by the placenta and secreted into the maternal
circulation, but at much lower levels than seen for CRH (Flo­
rio, 2002) . After labor begins, maternal plasma CRH levels rise
even further (Petraglia, 1 989, 1 990) .
he biological function of CRH synthesized in the placenta,
membranes, and decidua has been somewhat deined. CRH
receptors are present in many tissues including placenta. Tro­
phoblast, amniochorion, and decidua express both CRH-R1
and CRH-R2 receptors and several variant receptors (Florio,
2000) . Both CRH and urocortin enhance trophoblast secre­
tion of adrenocorticotropic hormone (ACTH) , supporting an
autocrine-paracrine role (Petraglia, 1 999) . Large amounts of
trophoblast CRH enter maternal blood.
Other proposed biological roles include induction of
smooth-muscle relaxation in vascular and myometrial tissue
and immunosuppression. The physiological reverse, however,
induction of myometrial contractions, has been proposed for
the rising CRH levels seen near term. One hypothesis sug­
gests that CRH may be involved with parturition initiation
(Wadhwa, 1 998) . Some evidence suggests that urocortin 2
expression is induced at term and induces expression of pro in­
lammatory markers and prostaglandin F receptor expression
in the placenta and myometrium (Voltolini, 20 1 5) . Prosta­
glandin formation in the placenta, amnion, chorion laeve,
and decidua is increased with CRH treatment Oones, 1 989b).
hese observations further support a potential action in par­
turition timing.
Glucocorticoids act in the hypothalamus to inhibit CRH
release, but in the trophoblast, glucocorticoids stimulate CRH
gene expression Oones, 1 989a; Robinson, 1 988). hus, there
may be a novel positive feedback loop in the placenta by which
placental CRH stimulates placental ACTH to stimulate fetal
and maternal adrenal glucocorticoid production with subse­
quent stimulation of placental CRH expression (Nicholson,
200 1 ; Riley, 1 99 1 ) .
Growth hormone-releasing hormone has an unknown role
(Berry, 1 992) . Ghrelin is another regulator of hGH secretion
that is produced by placental tissue (Horvath, 200 1 ) . Tropho­
blast ghrelin expression peaks at midpregnancy and is a para­
crine regulator of diferentiation or is a potential regulator of
human growth hormone variant production, described next
(Fuglsang, 2005; Gualillo, 200 1 ) .
1 01
1 02
Pl acentati o n, E m b ryog enesis, a n d Feta l Deve l o p m ent
Pitu ita ry-L i ke Hormones
ACTH, lipotropin, and �-endorphin, which are all proteolytic
products of pro-opiomelanocortin, are recovered from placen­
tal extracts (Genazzani, 1 975; Odagiri, 1 979) . he physiologi­
cal action of placental ACTH is unclear. As discussed, placental
CRH stimulates synthesis and release of chorionic ACTH.
A human growth hormone variant (hGH- J that is not
expressed in the pituitary is expressed in the placenta. The gene
encoding hGH-V is located in the hGH-hPL gene cluster on
chromosome 1 7. Sometimes referred to as placental growth
hormone, hGH-V is a 1 9 1 -amino-acid protein that difers in
1 5 amino acid positions from the sequence for hGH. Although
hGH-V retains growth-promoting and antilipogenic functions
similar to those of hGH, it has reduced diabetogenic and lac­
togenic functions relative to hGH (Vickers, 2009) . Placental
hGH-V presumably is synthesized in the syncytiotrophoblast.
It is believed that hGH-V is present in maternal plasma by 2 1 to
26 weeks' gestation, rises in concentration until approximately
36 weeks, and remains relatively constant thereafter. There is a
correlation between the levels of hGH-V in maternal plasma
and those of insulin-like growth factor- I . lso, hGH-V secre­
tion by trophoblast in vitro is inhibited by glucose in a dose­
dependent manner (Patel, 1 995). Overexpression of hGH-V in
mice causes severe insulin resistance, making it a likely candi­
date to mediate insulin resistance of pregnancy (Liao, 20 1 6) .
Relax i n
Expression o f relaxin has been demonstrated i n human corpus
luteum, decidua, and placenta (Bogic, 1 995). This peptide is
synthesized as a single, 1 05-amino-acid preprorelaxin molecule
that is cleaved to A and B molecules. Relaxin is structurally
similar to insulin and insulin-like growth factor. Two of the
three relaxin genes-H2 and H3-are transcribed in the cor­
pus luteum (Bathgate, 2002; H udson, 1 983, 1 984) . Decidua,
placenta, and membranes express H1 and H2 (Hansell, 1 99 1 ) .
The rise i n maternal circulating relaxin levels seen i n early
pregnancy is attributed to corpus luteum secretion, and levels
parallel those of hCG . Relaxin, along with rising progesterone
levels, may act on myometrium to promote relaxation and the
quiescence of early pregnancy (Chap. 2 1 , p. 407) . In addition,
the production of relaxin and relaxin-like factors within the
placenta and fetal membranes may play an autocrine-paracrine
role in postpartum regulation of extracellular matrix remodel­
ing (Qin, 1 997a,b) . One important relaxin function is enhance­
ment of the glomerular iltration rate (Chap. 4, p. 66) .
Pa rat hyroid Hormone-Related Protei n
I n pregnancy, circulating parathyroid hormone-related pro­
tein (PTH-rP) levels are significantly elevated within maternal
but not fetal circulation (Bertelloni, 1 994; Saxe, 1 997) . Many
functions of this hormone have been proposed. PTH-rP syn­
thesis is found in several normal adult tissues, especially in
reproductive organs that include myometrium, endometrium,
corpus luteum, and lactating mammary tissue. PTH-rP is not
produced in the parathyroid glands of normal adults. Placenta­
derived PTH-rP may have an important function to regulate
genes involved in transfer of calcium and other solutes. It also
contributes to fetal mineral homeostasis in bone, amnionic
luid, and the fetal circulation (Simmonds, 20 1 0) .
Lepti n
This hormone is normally secreted by adipocytes. It functions
as an antiobesity hormone that decreases food intake .through
its hypothalamic receptor. It also regulates bone growth and
immune unction (Cock, 2003; La Cava, 2004) . In the pla­
centa, leptin is synthesized by both cytotrophoblasts and syncy­
tiotrophoblast (Henson, 2002) . Relative contributions of leptin
from maternal adipose tissue versus placenta are currently not
well defined, although recent evidence highlights a key regula­
tory role of placental leptin in placental amino acid transport
and fetal growth (Rosario, 20 1 6a) . Maternal serum levels are sig­
nificantly higher than those in nonpregnant women. Fetal leptin
levels correlate positively with birthweight and likely function in
fetal development and growth. Studies suggest that reductions in
leptin availability contribute to adverse fetal metabolic program­
ing in intrauterine growth-restricted ofspring (Nusken, 20 1 6) .
N e u ropeptide Y
This 36-amino-acid peptide is widely distributed in brain. It
also is found in sympathetic neurons innervating the cardiovas­
cular, respiratory, gastrointestinal, and genitourinary systems.
Neuropeptide Y has been isolated from the placenta and local­
ized in cytotrophoblasts (Petraglia, 1 989) . Trophoblasts possess
neuropeptide Y receptors, and treatment of these with neuro­
peptide Y causes CRH release (Robidoux, 2000) .
I n h i bi n a n d Activin
hese glycoprotein hormones are expressed in male and female
reproductive tissues and belong to the transforming growth
factor-� family Gones, 2006) . Inhibin is a heterodimer made
up of one a-subunit and one of two distinct �-subunits,
either �A or �B. his yields either inhibin A or inhibin B,
respectively. Activin is formed by the combination of the
two �-subunits. Activin, inhibin, and their respective recep­
tors are expressed in the placenta. Both activin and inhibin A
have proposed functions during cytotrophoblast fusion into
the syncytiotrophoblast (Debieve, 2000; Jones, 2006) . Activin
also stimulates production of placental hormones such as hCG,
hPL, progesterone, and estrogen (Luo, 2002; Morrish, 1 99 1 ;
Petraglia, 1 989; Song, 1 996) . Inhibin A opposes activin action
in the placenta to inhibit production of hCG and steroido­
genesis (Petraglia, 1 989) . Abnormal levels of inhibin or activin
correlate with placental pathologies. For example, elevation in
inhibin A levels in the second trimester is indicative of fetal
Down syndrome. Further, low inhibin levels early in pregnancy
may indicate pregnancy failure (Prakash, 2005; Wallace, 1 996) .
Elevations in circulating inhibin and activin levels are reported
in women with preeclampsia (Bersinger, 2003) .
• Placental Progesterone Production
After 6 to 7 weeks' gestation, little progesterone is produced in
the ovary (Diczfalusy, 1 96 1 ) . Surgical removal of the corpus
luteum or even bilateral oophorectomy during the 7th to 1 0th
week does not decrease excretion rates of urinary pregnanediol,
I m pl a ntation a nd P lacenta l Development
Progesterone
1 00.0
' 50.0
E
,
s
'0
"
n
..
)
a
"
)
Estradiol
Estriol
1 0 .0
Estrone
5.0
)
l
'c
0
)
:
l
E
u
::
/
1 .0
0.5
n
u
Estetrol
Estradiol
( nonpregnant)
0.1
0.05
4
8 1 2 1 6 20 24 28 32 36 40
Gestational age (weeks)
FIGURE 5-1 9 Plasma levels of progesterone, estrad iol, estrone,
estetrol, a n d estriol in women d u ring the course of gestation.
(Mod ified a n d red rawn with perm ission from Mesiano S: The endo­
crinology of h u m a n preg nancy a nd fetoplacental neu roendocri ne
development. I n Stra uss J F, Ba rbieri RL (eds) Yen a nd Jaffe's Repro­
ductive Endocrinology: P hysiology, Pathophysiology, a n d C l i n ica l
Management, 6th ed. P h iladeph ia, Sa u nders, 2009.)
the principal urinary metabolite of progesterone. Before this
time, however, corpus luteum removal will result in spontane­
ous abortion unless an exogenous progestin is given (Chap. 63,
p. 1 1 98) . After approximately 8 weeks, the placenta assumes
progesterone secretion, resulting in a gradual increase in mater­
nal serum levels throughout pregnancy (Fig. 5- 1 9) . By term,
these levels are 1 0 to 5000 times those found in nonpregnant
women, depending on the stage of the ovarian cycle.
The daily production rate of progesterone in late, normal,
singleton pregnancies approximates 250 mg. In mulrifetal preg­
nancies, the daily production rate may exceed 600 mg. Proges­
terone is synthesized from cholesterol in a two-step enzymatic
reauiuI1. r.l�., L-l1UI:�L:l Ul ;�
C0il
v'ci'tC.
tv
plcg.cidciC ';;ithi�
the mitochondria, in a reaction catalyzed by cytochrome P450
cholesterol side-chain cleavage enzyme. Pregnenolone leaves the
mitochondria and is converted to progesterone in the endoplas­
mic reticulum by 33-hydroxysteroid dehydrogenase. Progester­
one is released immediately through a process of difusion.
Although the placenta produces a prodigious amount of
progesterone, the syncytiotrophoblast has a limited capacity
for cholesterol biosynthesis. Radiolabeled acetate is incorpo­
rated into cholesterol by placental tissue at a slow rate. he
rate-limiting enzyme in cholesterol biosynthesis is 3-hydroxy3-methylglutaryl coenzyme A (HMG-CoA) reductase. Because
of this, the placenta must rely on an exogenous source, that
is, maternal cholesterol, for progesterone formation. he tro­
phoblast preferentially uses LDL cholesterol for progesterone
biosynthesis (Simpson, 1 979, 1 980) . This mechanism difers
from placental production of estrogens, which relies principally
on fetal adrenal precursors.
Although there is a relationship between fetal well-being and
placental estrogen production, this is not the case for placen­
tal progesterone. Thus, placental endocrine function, including
the formation of protein hormones such as hCG and proges­
terone biosynthesis, may persist for weeks after fetal demise.
he metabolic clearance rate of progesterone in pregnant
women is similar to that found in men and nonpregnant
women. During pregnancy, the plasma concentration of
5a-dihydroprogesterone disproportionately rises due to syn­
thesis in syncytiotrophoblast from both placenta-produced
progesterone and fetus-derived precursor (Dombroski, 1 997) .
hus, the concentration ratio of this progesterone metabolite
to progesterone is elevated in pregnancy. The mechanisms for
this are not deined completely. Progesterone also is converted
to the potent mineralocorticoid deoxycorticosterone in preg­
nant women and in the fetus. The concentration of deoxy­
corticosterone is strikingly higher in both maternal and fetal
compartments (see Table 5- 1 ) . The extraadrenal formation of
deoxycorticosterone from circulating progesterone accounts for
most of its production in pregnancy (Casey, 1 982a,b) .
• Placental Estrogen Production
During the first 2 to 4 weeks of pregnancy, rising hCG lev­
els maintain production of estradiol in the maternal corpus
luteum. Production of both progesterone and estrogens in the
maternal ovaries drops signiicantly by the 7th week of preg­
nancy. At this time, there is a luteal-placental transition. By the
7th week, more than half of estrogen entering maternal circula­
tion is produced in the placenta (MacDonald, 1 965a; Siiteri,
1 963, 1 966) . Subsequently, the placenta produces a continually
increasing magnitude of estrogen. Near term, normal human
pregnancy is a hyperestrogenic state, and syncytiotrophoblast is
producing estrogen in amounts equivalent to that produced in
1 day by the ovaries of no fewer than 1 000 ovulatory women.
This hyperestrogenic state terminates abruptly after delivery of
the placenta.
Biosynth esis
In human trophoblast, neither cholesterol nor, in turn, proges­
:e�8!e :�� �e�.'e !s
F"�C�!!S0!" Fo r �'tr0g�n hi)"yn th �." i s . Th i � i s
because steroid 17a-hydroxylasel1,20-yase (CP1 7Al) is not
expressed in the human placenta. This essential enzyme con­
verts 1 7-0H progesterone (a C2 I steroid) to androstenedione,
which is a C ' 9 steroid and an estrogen precursor. Consequently,
the conversion of C2I steroids to C ' 9 steroids is not possible.
However, dehydroepiandrosterone (DHEA) and its sulfate
(DHEA-S) are also C ' 9 steroids and are produced by maternal
and fetal adrenal glands. These two steroids can serve as estrogen
precursors (Fig. 5-20) . Ryan ( 1 959a) found that the placenta
had an exceptionally high capacity to convert appropriate C'9
steroids to estrone and estradiol. The conversion of DHEA-S
to estradiol requires placental expression of four key enzymes
1 03
1 04
P l ace ntati on, E m b ryog enesi s, a n d Feta l Deve l o p m e nt
LDL cholesterol
�
narcua_
te rn--�.
lcil atM_
i o�
7
___
"
,
f
I
, ,,
,,
Estriol
�
,
,,,
i
i
i
"
StAR
! Estradiol !
i
i
/
"
Side-chain cleavage
i
i
i
"
CYP 1 7
1 7�HSD 1
t t
i
i
Aromatase
t t
t t
3�H S D 1
Placenta
Su lfatase
.
Fetal adrenal
"
Su lfotransferase
�
-------------- ! DH EA-S I
.�
..
!
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 1 60H - D H EA- S
!
FIGURE 5-20 Schematic presentation of estrogen biosynthesis in the h u m a n placenta. Dehyd roepia nd rosterone su lfate (DH EAS), secreted
in prod igious a mou nts by the fetal a d renal g l a nds, is converted to 1 6a-hyd roxydehyd roepiand rosterone sulfate ( 1 6aO H D H EAS) in the feta l
l iver. These steroids, D H EAS a n d 1 6aOH DH EAS, a re converted i n the placenta to estrogens, that is, 1 7�-estradiol (E) a nd estriol (E3). Near
term, h a lf of E 2 is derived from fetal a d re n a l DH EAS a n d h a lf from maternal DH EAS. On the other h a nd, 90 percent of E3 in the placenta
a ri ses from feta l 1 6aOH DH EAS and o n ly 1 0 percent from a l l other sou rces.
that are located principally in syncytiotrophoblast (Bonenfant,
2000; Salido, 1 990) . First, the placenta expresses high levels of
steroid sulfatase (STS) , which converts the conjugated DHEA­
S to DHEA. DHEA is then acted upon by 33-hydroxysteroid
dehydrogenase type 1 (33 HSD) to produce androstenedione.
Cytochrome P450 aromatase (CYP 1 9) then converts andro­
stenedione to estrone, which is then converted to estradiol by
1 73-hydroxysteroid dehydrogenase type 1 ( 1 73 HSD l ) .
DHEA-S i s the major precursor o f estrogens i n pregnancy
(Baulieu, 1 963; Siiteri, 1 963) . However, maternal adrenal
glands do not produce suicient amounts of DHA-S to
account for more than a fraction of total placental estrogen bio­
synthesis. he fetal adrenal glands are quantitatively the most
important source of placental estrogen precursors in human
pregnancy. hus, estrogen production during pregnancy relects
the unique interactions among fetal adrenal glands, fetal liver,
placenta, and maternal adrenal glands.
D i rectiona l Secretion
More than 90 percent of estradiol and estriol formed in syncy­
tiotrophoblast ' enters maternal plasma (Gurpide, 1 966) . And,
85 percent or more of placental progesterone enters maternal
plasma, and little maternal progesterone crosses the placenta to
the fetus (Gurpide, 1 972) .
his directional movement of newly formed steroid into the
maternal circulation stems from basic characteristics of hemo­
chorioendothelial placentation. In this system, steroids secreted
from syncytiotrophoblast can enter maternal blood directly.
Steroids that leave the syncytium do not enter fetal blood
directly. hey must irst traverse the cytotrophoblast layer and
then enter the stroma of the villous core and then fetal capil­
laries. From either of these spaces, steroids can reenter the syn­
cytium. he net result of this hemochorial arrangement is that
entry of steroids into the maternal circulation is substantially
greater than that into fetal blood.
FETAL ADRENAL G LAND-PLACENTAL
I NTERACTIONS
Morphologically, functionally, and physiologically, the fetal
adrenal glands are remarkable. At term, the fetal adrenal glands
weigh the same as those of the adult. More than 85 percent
of the fetal gland is composed of a unique fetal zone, which
has a great capacity for steroid biosynthesis. Daily steroid
production of fetal adrenal glands near term is 1 00 to 200
mg/d. This compares with resting adult steroid secretion of 30
to 40 mg/d.
I m pl a ntat i o n a n d P lacental Development
The fetal zone is lost in the irst year of life and is not present
in the adult. In addition to ACTH, fetal adrenal gland growth
is influenced by factors secreted by the placenta. This is exem­
pliied by the continued growth of the fetal glands throughout
gestation and by rapid involution immediately after birth and
placental delivery.
• Placental Estriol Synthesis
Estradiol is the primary placental estrogen product at term. In
addition, significant levels of estriol and estetrol are found in
the maternal circulation, and levels also rise, particularly late
in gestation (see Fig. 5- 1 9) . hese hydroxylated forms of estro­
gen derive from the placenta using substrates formed by the
combined eforts of the fetal adrenal gland and fetal liver. For
this, high levels of fetal hepatic 1 6a-hydroxylase act on adre­
nal-derived steroids. Ryan ( 1 959b) and MacDonald and Siiteri
( 1 965b) found that 1 6a-hydroxylated C19 steroids, particu­
larly 1 6a-hydroxydehydroepiandrosterone ( 1 6-0HDHEA) ,
were converted to estriol by placental tissue. Thus, the dispro­
portionate increase in estriol formation during pregnancy is
accounted for by placental synthesis of estriol principally from
plasma-borne 1 6-0HDHEA-sulfate. Near term, the fetus is
the source of 90 percent of placental estriol and estetrol precur­
sors in normal human pregnancy.
Maternal estriol and estetrol are produced almost solely by
fetal steroid precursors. hus, in the past, levels of these steroids
were used as an indicator of fetal well-being. However, the low
sensitivity and speciicity of such tests have caused them to be
discarded.
• Fetal Adrenal Steroid Precursor
The precursor for fetal adrenal steroidogenesis is cholesterol.
he steroid biosynthesis rate in the fetal gland is so great that its
steroidogenesis alone is equivalent to a fourth of the total daily
LDL cholesterol turnover in adults. Fetal adrenal glands syn­
thesize cholesterol from acetate. All enzymes involved in choles­
terol biosynthesis are elevated compared with those of the adult
adrenal gland (Rainey, 200 1 ) . Thus, the de novo cholesterol
synthesis rate by fetal adrenal tissue is extremely high. Even so,
it is insuicient to account for the steroids produced by fetal
adrenal glands. Therefore, cholesterol must be assimilated from
the fetal circulation and mainly from LDL (Carr, 1 980, 1 98 1 b,
1 982; Simpson, 1 979) .
Most fetal plasma cholesterol arises by de novo synthesis in
the fetal liver (Carr, 1 984) . The low LDL cholesterol level in
fetal plasma is not the consequence of impaired fetal LDL syn­
thesis, but instead results from the rapid use of LDL by the fetal
adrenal glands for steroidogenesis (Parker, 1 980, 1 983) .
• Fetal Conditions Afecting
Estrogen Production
Several fetal disorders alter the availability of substrate for pla­
cental steroid synthesis and thus highlight the interdependence
of fetal development and placental function.
Fetal demise is followed by a striking reduction in urinary
estrogen levels. Similarly, after ligation of the umbilical cord
with the fetus and placenta left in situ, placental estrogen
production declines markedly (Cassmer, 1 959) . However,
as previously discussed, placental progesterone production is
maintained. In sum, an important source of precursors of pla­
cental estrogen-but not progesterone-biosynthesis is elimi­
nated with fetal death.
Anencephalic etuses have markedly atrophic adrenal glands.
his stems from absent hypothalamic-pituitary function,
which precludes adrenal stimulation by ACTH. With absence
of the adrenal cortex fetal zone, the placental formation of
estrogen-especially estriol-is severely limited because of
diminished availability of C 1 9 steroid precursors. Indeed, uri­
nary estrogen levels in women pregnant with an anencephalic
fetus are only about 1 0 percent of those found in normal preg­
nancy (Frandsen, 1 96 1 ) . With an anencephalic fetus, almost
all estrogens produced arise from placental use of maternal
plasma DHEA-S.
Fetal adrenal cortical hypoplasia occurs in perhaps 1 in 1 2, 500
births (McCabe, 200 1 ) . Estrogen production in these pregnan­
cies is limited, which suggests the absence of C19 precursors.
Fetal-placental suatase diciency is associated with very
low estrogen levels in otherwise normal pregnancies (France,
1 969) . Namely, sulfatase deficiency precludes the hydrolysis of
C19 steroid sulfates, the fi r st enzymatic step in the placental use
of these circulating prehormones for estrogen biosynthesis. This
deficiency is an X-linked disorder, and thus all afected fetuses
are male. Its estimated frequency is 1 in 2000 to 5000 births
and is associated with delayed labor onset. It also is associated
with the development of ichthyosis in afected males later in life
(Bradshaw, 1 986) .
Fetal-placental aromatase diciency i s a rare autosomal reces­
sive disorder in which individuals cannot synthesize endogenous
estrogens (Grumbach, 20 1 1 ; Simpson, 2000) . To recall, fetal
adrenal DHA-S is converted in the placenta to androstene­
dione, but in cases of placental aromatase deiciency, andro­
stenedione cannot be converted to estradiol. Rather, androgen
metabolites of DHEA produced in the placenta, including
androstenedione and some testosterone, are secreted into the
maternal or fetal circulation, or both. This can cause virilization
of the mother and the female fetus (Belgorosky, 2009; Harada,
1 992; Shozu, 1 99 1 ) .
Trisomy 21-Down syndrome screening searches for abnor­
mal levels of hCG, alpha-fetoprotein, and other analytes (Chap.
1 4, p. 28 1 ) . It was discovered that serum unconjugated estriol
levels were low in women with Down syndrome fetuses (Benn,
2002) . The likely reason for this is inadequate formation of C19
steroids in the adrenal glands of these trisomic fetuses.
Fetal eythroblastosis in some cases of severe fetal D-antigen
alloimmunization can lead to elevated maternal plasma estro­
gen levels. A suspected cause is the greater placental mass from
hypertrophy, which can be seen with such fetal hemolytic ane­
mia (Chap. 1 5, p. 300) .
• Maternal Conditions Afecting
Estrogen Production
Glucocorticoid treatment can cause a striking reduction in pla­
cental estrogen formation. Glucocorticoids inhibit ACTH
1 05
1 06
P l acentation, Em bryogenesis, a n d Feta l Deve l opment
secretion from the maternal and fetal pituitary glands. This
diminishes maternal and fetal adrenal secretion of the placental
estrogen precursor DHEA-S.
With Addison disease, pregnant women show lower estrogen
levels, principally estrone and estradiol levels (Baulieu, 1 956).
The fetal adrenal contribution to estriol synthesis, particularly
in later pregnancy, is quantitatively much more important.
Maternal androgen-producing tumors can present the pla­
centa with elevated androgen levels. Fortunately, placenta is
extraordinary eicient in the aromatization of C19 steroids. For
example, Edman and associates ( 1 98 1 ) found that virtually all
androstenedione entering the intervillous space is taken up by
syncytiotrophoblast and converted to estradiol. None of this C 1 9
steroid enters the fetus. Second, a female fetus i s rarely virilized
if there is a maternal androgen-secreting tumor. The placenta
eiciently converts aromatizable C19 steroids, including testos­
terone, to estrogens, thus precluding transplacental passage.
Indeed, virilized female fetuses of women with an androgen­
producing tumor may be cases in which a nonaromatizable
C19 steroid androgen is produced by the tumor-for example,
5a-dihydrotestosterone. Another explanation is that testoster­
one is produced very early in pregnancy in amounts that exceed
the placental aromatase capacity at that time.
Complete hydatidiorm mole and gestational trophoblastic neo­
plasias lack a fetus and also a fetal adrenal source of C19 steroid
precursors for trophoblast estrogen biosynthesis. Consequently,
placental estrogen formation is limited to the use of C 19 steroids
from the maternal plasma, and therefore estradiol is principally
produced (MacDonald, 1 964, 1 966) .
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111
C H A PT E R 6
P l a ce nta l A b n o rm a l i t i es
NORMAL PLACENTA . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 1 1
SHAPE AND SIZE VARIANTS . . . . . . . . . . . . . . . . . . . . . . 1 1 2
EXTRACHORIAL PLACENTATION . . . . . . . . . . . . . . . . . . 1 1 3
CI RCU LATORY DISTU RBANCES . . . . . . . . . . . . . . . . . . . 1 1 3
At minimum, the placenta and cord should be inspected in the
delivery room. he decision to request pathological examina­
tion should be based on clinical and placental findings (Red­
line, 2008; Roberts, 2008) . Listed in Table 6- 1 are some of the
indications at Parkland Hospital for placental anatomical and
histopathological examination.
PLACENTAL CALCI F I CATION. . . . . . . . . . . . . . . . . . . . . . 1 1 5
PLACENTAL TU MORS . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 1 5
AMNIOCHORION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 1 6
UMBI LICAL CORD. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 1 7
The placenta, as a rule, presents more or less rounded outlines,
but now and again when inserted in the neighbourhood of
the internal os it may take on a horseshoe-like appearance,
its two branches running partialy around the oriice.
-J. Whitridge Williams ( 1 903)
he placenta is a fantastic organ in its own right. As discussed
in Chapter 5 (p. 88), it provides the indispensable interface
between mother and fetus. Indeed, placental anatomy, physiol­
ogy, and molecular structure remain some of the most intrigu­
ing and understudied topics in obstetrics.
Although a placental examination by the obstetrician is rec­
ommended, by consensus, routine pathological examination is
not mandatory. Indeed, speciic conditions that merit submis­
sion for detailed inspection are still debated. By way of example,
the College ofAmerican Pathologists has recommended placen­
tal examination for an extensive list of indications (Langston,
1 997) . Data, however, are insuicient to support all of these.
NORMAL PLACENTA
At term, the typical placenta weighs 470 g, is round to oval
with a 22-cm diameter, and has a central thickness of 2 . 5 cm
(Benirschke, 20 1 2) . It is composed of a placental disc, extra­
placental membranes, and three-vessel umbilical cord. The
disc surface that lies against the uterine wall is the basal plate,
which is divided by clefts into portions-termed cotyledons.
he fetal surface is the chorionic plate, into which the umbili­
cal cord inserts, typically in the center. Large fetal vessels that
originate from the cord vessels then spread and branch across
the chorionic plate before entering stem villi of the placenta
parenchyma. In tracing these, fetal arteries almost invariably
cross over veins. he chorionic plate and its vessels are covered
by thin amnion, which can be easily peeled away from a post­
delivery specimen.
As recommended by the American Institute of Ultrasound
in Medicine (20 1 3), placental location and relationship to the
internal cervical os are recorded during prenatal sonographic
examinations. As visualized ultrasonically, the normal placenta
is homogenous and 2 to 4 cm thick, lies against the myome­
trium, and indents into the amnionic sac. The retroplacental
space is a hypoechoic area that separates the myometrium from
the basal plate and measures less than 1 to 2 cm. The umbilical
cord is also imaged, its fetal and placental insertion sites exam­
ined, and its vessels counted.
Many placental lesions can be identiied grossly or sono­
graphically, but other abnormalities require histopathological
examination for clariication. A detailed description of these
1 12
Place ntatio n , E m b ryogenesis, and Feta l Deve l o p m e nt
TABLE 6-1 . Some I nd ication s for Placenta l Path olog ica l
Exa m i nationa
Maternal Indications
Abru pti o n
Ante pa rt u m i n fection with feta l ri sks
Anti-C D E a l l o i m m u n ization
Ces a re a n hysterectomy
O l i gohydra m n i os o r hyd ra m n ios
Peri part u m fever o r i nfection
P reter m d e l i very
Postterm d e l ive ry
Seve re tra u ma
S u s pected p l ace nta l i nj u ry
System i c d i so rd e rs with known effects
Th i c k or viscid meco n i u m
U nexp l a i n ed l ate preg na ncy b leed i n g
U nexpla i ned o r rec u rrent preg n a n cy c o m p l i cati o n s
Feta l and Neonatal I nd ications
Ad m i ssion to an acute ca re n u rsery
B i rth we i g h t � 1 0th or � 95th percent i l e
Feta ! a n e m i a
Feta l o r n eonata l com p rom ise
Neon ata l seizures
Hyd rops feta l i s
I n fectio n o r sepsis
Maj o r a n o m a l ies o r a bnormal ka ryotype
Mu ltifeta l gestati o n
Sti l l b i rt h o r n eo nata l death
Va n is h i ng twi n beyond the fi rst tri mester
Placenta l Indications
G ross lesions
Marg i na l o r ve l a m ento u s cord i n se rtion
Ma rked ly a bnormal placenta l shape o r size
Ma rked ly a d h e red placenta
Te rm cord < 32 cm or > 1 00 cm
U m b i l ical cord lesions
a l n d i cat i o n s a re o rga n ized a l pha betica l ly.
is beyond the scope of this chapter, and interested readers
are referred to textbooks by Benirschke (20 1 2) , Fox (2007) ,
and Faye-Petersen (2006) and their colleagues. Moreover,
the placenta accrete syndrome and gestational trophoblas­
tic disease are presented in detail in Chapters 20 and 4 1 ,
respectively.
SHAPE A N D SIZE VARIANTS
Of variants, placentas may infrequently form as separate, nearly
equally sized discs. his bilobate placenta may also be called
bipartite placenta or placenta duplex. In these, the cord inserts
between the two placental lobes-either into a connecting
chorionic bridge or into intervening membranes. A placenta
containing three or more equivalently sized lobes is rare and
termed multilobate. Unlike this equal distribution, one or more
FIGURE 6-1 Succentu riate lobe. A. Vessels extend from the main
place ntal disc to s u pply the s m a l l rou nd succentu riate l obe located
beneath it. (Used with permission from Dr. Jaya George.) B. Sono­
g ra ph ic i ma g i n g with color Doppler shows the m a i n placental disc
i m pla nted posteriorly (asterisk). The succenturiate lobe is located
on the anterior uteri ne wa l l across the a m n ionic cavity. Vessels a re
identified as the long red a n d blue crossing tu b u l a r structu res that
travel with i n the membranes to con nect these two portions of
place nta.
disparately smaller accessory lobes-succenturiate lobes-may
develop in the membranes at a distance from the main placenta
(Fig. 6- 1 ) . hese lobes have vessels that course through the
membranes. Of clinical importance, if these vessels overlie the
cervix to create a vasa previa, dangerous fetal hemorrhage can
follow vessel laceration (p. 1 1 8) . n accessory lobe can also be
retained in the uterus after delivery to cause postpartum uterine
atony and hemorrhage or later endometritis.
Rarely, the placental surface area varies from the norm. With
placenta membranacea, villi cover all or nearly all the uterine
cavity. This may occasionally give rise to serious hemorrhage
because of associated placenta previa or accreta (Greenberg,
1 99 1 ; Pereira, 20 1 3) . A ring-shaped placenta may be a variant
of placenta membranacea. his placenta is annular, and a par­
tial or complete ring of placental tissue is present. hese abnor­
malities appear to be associated with a greater likelihood of
P lacenta l Abnorm a l ities
antepartum and postpartum bleeding and fetal-growth restric­
tion (Faye-Petersen, 2006; Steemers, 1 995). With placenta
fenestrata, the central portion of a placental disc is missing. In
some instances, there is an actual hole in the placenta, but more
often, the defect involves only villous tissue, and the chorionic
plate remains intact. Clinically, it may erroneously prompt a
search for a retained placental cotyledon.
During pregnancy, the normal placenta increases its thick­
ness at a rate of approximately 1 mm per week. lthough not
measured as a component of routine sonographic evaluation,
this thickness typically does not exceed 40 mm (Hoddick,
1 985). Placentomegay deines those thicker than 40 mm and
commonly results from striking villous enlargement. his may
be secondary to maternal diabetes or severe maternal anemia, or
to fetal hydrops, anemia, or infection caused by syphilis, toxo­
plasmosis, parvovirus, or cytomegalovirus. In these conditions,
the placenta is homogeneously thickened. Less commonly with
placentomegaly, fetal parts are present, but villi are edematous
and appear as small placental cysts, such as in cases of par­
tial mole (Chap. 20, p. 39 1 ) . Cystic vesicles are also seen with
placental mesenchymal dysplasia. Vesicles in this rare condition
correspond to enlarged stem villi, but unlike molar pregnancy,
trophoblast proliferation is not excessive (Woo, 20 1 1 ) .
Rather than villous enlargement, placentomegaly often
may result from collections of blood or ibrin, which impart
heterogeneity to the placenta. Examples of this are discussed
on page 1 1 4 and include massive perivillous fibrin deposition,
intervillous or subchorionic thromboses, and large retropla­
cental hematomas.
EXTRACHORIAL PLACENTATION
he chorionic plate normally extends to the periphery of the
placenta and has a diameter similar to that of the basal plate.
With extrachorial placentation, however, the chorionic plate
fails to extend to this periphery and leads to a chorionic plate
that is smaller than the basal plate (Fig. 6-2) . Circummargin­
ate and circumvallate placentas are the two types. In a circum­
marginate placenta, ibrin and old hemorrhage lie between the
Circummarginate
placenta and the overlying sheer amniochorion. In contrast,
with a circumvallate placenta, the chorion periphery is a thick­
ened, opaque, gray-white circular ridge composed of a double
fold of chorion and amnion. Sonographically, the double fold
can be seen as a thick, linear band of echoes extending from
one placental edge to the other. On cross section, however, it
appears as two "shelves, " with each lying above an opposing
placental margin (see Fig. 6-2) . his anatomy can help difer­
entiate this shelf from amnionic bands and amnionic sheets,
which are described on page 1 1 6.
In relatively small observational studies of circumvallate pla­
centa diagnosed postpartum, it was associated with increased
risk for antepartum bleeding, abruption, fetal demise, and
preterm birth (Lademacher, 1 98 1 ; Suzuki, 2008; Taniguchi,
20 1 4) . In a prospective sonographic investigation of 1 7 cases,
however, Shen and associates (2007a) found most circumval­
late placentas to be transient. Persistent cases were benign. In
general, most otherwise uncomplicated pregnancies with either
type of extrachorial placentation have normal outcomes, and
no increased surveillance is usually required.
CIRCU LATORY DISTURBANCES
Functionally, placental perfusion disorders can be grouped
into: ( 1 ) those in which maternal blood low to or within the
intervillous space is disrupted, and (2) those with disturbed
fetal blood flow through the villi. These lesions are frequently
identiied in the normal, mature placenta. Although they can
limit maximal placental blood flow, functional reserve within
the placental prevents harm in most cases. Indeed, some esti­
mate that up to 30 percent of placental villi can be lost without
untoward fetal efects (Fox, 2007) . If extensive, however, these
lesions can profoundly limit fetal growth.
Lesions that disrupt perfusion are frequently seen grossly
or sonographically, whereas smaller lesions are seen only his­
tologically. With sonography, many of these, such as sub­
chorionic fibrin deposition, perivillous ibrin deposition , and
intervillous thrombosis, appear as focal sonolucencies within
the placenta. Importantly, in the absence of maternal or fetal
Circumvallate
Double fold of
amnion & chorion
Amnion
Fibrin
deposition
A
deposition
FIGURE 6-2 A. In this i l l u stration, circu m m a rg i nate (left) and circumva l l ate (right) varieties of extrachoria l pl acentation a re s h own.
A circ u m marginate place nta is covered by a s i n g le layer of a m n iochorion. B. This tra nsa bdomi n a l g ray-scale sonog ra phic image s hows a
circumva l late placenta. The double fo l d of a m n ion a n d chorion creates a broad, opa q u e wh ite ri ng a nd ridge on the feta l s u rface.
1 13
1 14
P l ace ntation, E m b ryogen esis, a n d Feta l Deve l o pment
complications, isolated placental sonolucencies are considered
incidental indings.
• Materna l Blood Flow Disruption
S u bc horion ic F i b r i n Deposition
These collections are caused by slowing of maternal blood low
within the intervillous space. In the portion of this space near
the chorionic plate, blood stasis is prominent and leads to sub­
sequent ibrin deposition. In viewing the placental fetal surface,
subchorionic lesions are commonly seen as white or yellow,
firm, round, elevated plaques j ust beneath the chorionic plate.
Pe rivi l l o u s F i b r i n D e position
Stasis of maternal blood flow around an individual villus also
results in fibrin deposition and can lead to diminished villous
oxygenation and necrosis of syncytiotrophoblast (Fig. 6-3) .
These small yellow-white placental nodules are grossly visible
within the parenchyma of a sectioned placenta. Within limits,
these relect normal placental aging.
Maternal Floor I nfarction. his extreme variant of perivillous
fibrin deposition is a dense ibrinoid layer within the placental
basal plate and is erroneously termed an infarction. Maternal
loor inarction has a thick, yellow or white, irm corrugated sur­
face that impedes normal maternal blood low into the intervil­
lous space. In specific cases that extend beyond the basal plate
to entrap villi and obliterate the intervillous space, the term
massive perivillousibrin deposition is used. The etiopathogenesis
is unclear, but maternal auto- or alloimmunity appears con­
tributory (Faye-Peterson, 20 1 7; Romero, 20 1 3) . Antiphospho­
lipid antibody syndrome and angiogenic factors involved with
preeclampsia have also been implicated (Sebire, 2002, 2003;
Whitten, 20 1 3) .
Subchorial
thrombosis
These lesions are not reliably imaged with prenatal sonog­
raphy, but they may create a thicker basal plate. Afected preg­
nancies are associated with miscarriage, fetal-growth restriction,
preterm delivery, and stillbirth (Andres, 1 990; Mandsager,
1 994) . Importantly, these adverse outcomes can recur in sub­
sequent pregnancies.
I nterv i l l o u s Th rombus
This is a collection of coagulated maternal blood normally
found in the intervillous space mixed with fetal blood from a
break in a villus. Grossly, these round or oval collections vary
in size up to several centimeters. hey appear red if recent or
white-yellow if older, and they develop at any placental depth.
Intervillous thrombi are common and typically not associated
with adverse fetal sequelae. Because there is potential for a
communication between maternal and fetal circulations, large
lesions can cause elevated maternal serum alpha-fetoprotein
levels (Salaia, 1 988).
I nfa rction
Chorionic villi themselves receive oxygen solely from maternal
circulation supplied to the intervillous space. Any uteroplacen­
tal disease that diminishes or obstructs this supply can result in
infarction of an individual villus. These are common lesions in
mature placentas and are benign in limited numbers. If numer­
ous, however, placental insuiciency can develop. When they
are thick, centrally located, and randomly distributed, they may
be associated with preeclampsia or lupus anticoagulant.
H e mato m a
As depicted in Figure 6-3, the maternal-placental-fetal unit
can develop several hematoma types. These include: ( 1 ) ret­
roplacental hematoma-between the placenta and its adjacent
decidua; (2) marginal hematoma-between the chorion and
Subam nionic hematoma
Fetal thrombotic
vasculopathy
Margi nal
hematoma ___
Perivillous -fibrinoid
deposition
Retroplacental ---.
hematoma
.:. :�.-��-7--- Maternal floor
i nfarction
F I G U R E 6-3 Potential s ites of matern a l ly and feta l ly related placenta l circ u latory distu rbances. (Ada pted from Faye-Petersen, 2006.)
Placenta l A b n o r m a l ities
decidua at the placental periphery-known clinically as sub­
chorionic hemorrhage; (3) subamnionic hematoma-these are
of fetal vessel origin and found beneath the amnion but above
the chorionic plate, and (4) subchorial thrombus along the roof
of the intervillous space and beneath the chorionic plate. With
this last type, massive subchorionic hematomas are also known as
a Breus mole.
Sonographically, hematomas evolve with time and appear
hyperechoic to isoechoic in the irst week after hemorrhage,
hypoechoic at 1 to 2 weeks, and inally, anechoic after 2 weeks.
Most subchorionic hematomas visible sonographically are fairly
small and of no clinical consequence. However, extensive ret­
roplacental, marginal, and subchorial collections have been
associated with higher rates of miscarriage, stillbirth, placen­
tal abruption, and preterm delivery (Ball, 1 996; Fung, 20 1 0;
vladu, 2006; Tuuli, 20 1 1 ) . In essence, placental abruption is a
large, clinically signiicant retroplacental hematoma.
• Fetal Blood Flow Disruption
Feta l Th ro m botic Vascu lo pathy
Placental lesions that arise from fetal circulatory disturbances
are also depicted in Figure 6-3 . Deoxygenated fetal blood
lows from the two umbilical arteries into arteries within the
chorionic plate that divide and send branches out across the
placental surface. hese eventually supply individual stem villi,
and their thrombosis will obstruct fetal blood low. Distal to
the obstruction, afected portions of the villus become non­
functional. Thrombi in limited numbers are normally found
in mature placentas. If many villi are afected, which can be
seen with preeclampsia, the fetus may sufer growth restriction,
stillbirth, or nonreassuring fetal heart rate patterns (Chisholm,
20 1 5; Lepais, 20 1 4; Saleemuddin, 20 1 0) .
Vi l lo u s Vas c u l a r Lesions
here is a spectrum of villous capillary lesions. Chorangiosis
describes an increased number of capillaries within terminal
villi. Its deinition requires ::: 10 capillaries to be present in
:::10 villi in ::: 10 ields viewed through a l O x microscope lens
(Altshuler, 1 984) . Clinically, long-standing hypoperfusion or
hypoxia is thought to be causative (Stanek, 20 1 6) . It is often
associated with maternal diabetes mellitus (Ogino, 2000) . Cho­
rangiomatosis describes increased capillary number in stem villi,
but terminal villi are spared. his inding has been linked
with fetal-growth restriction and anomalies (Bagby, 20 1 1 ) .
Despite these associations, the clinical signiicance of both vas­
cular conditions remains unclear. Chorioangiomas are described
subsequently.
S u ba m n io n ic H em atoma
As indicated earlier, these hematomas lie between the chori­
onic plate and amnion. They most often are acute events during
third-stage labor when cord traction ruptures a vessel near the
cord insertion.
Large chronic antepartum lesions may cause fetomaternal
hemorrhage or fetal-growth restriction (Deans, 1 998). They
also may be confused with other placental masses such as cho­
rio angioma. In most cases, Doppler interrogation will show
absent internal blood low within a hematoma and permit dif­
ferentiation (Sepulveda, 2000) .
PLACENTAL CALCI FICATION
Calcium salts can be deposited throughout the placenta but
are most common on the basal plate. Calciication accrues
with advancing gestation, and greater degrees are associated
with smoking and increasing maternal serum calcium levels
(Bedir Findik, 20 1 5 ; Klesges, 1 998; McKenna, 2005). These
hyperechoic deposits can easily be seen sonographically, and a
grading scale from 0 to 3 relects increasing calciication with
increasing numerical grade (Grannum, 1 979) . Following this
scheme, a grade 0 placenta is homogeneous, lacks calciication,
and displays a smooth, lat chorionic plate. A grade 1 placenta
has scattered echogenicities and subtle chorionic plate undu­
lations. Grade 2 shows echogenic stippling at the basal plate.
Large, echogenic comma shapes originate from an indented
chorionic plate, bur their curve falls short of the basal plate.
Last, a grade 3 placenta has echogenic indentations extending
from the chorionic plate to the basal plate, which create discrete
components that resemble cotyledons. Basal plate densities also
increase.
As a predictor, this grading scale is not useful for neona­
tal outcome near term (Hill, 1 983; McKenna, 2005; Montan,
1 986) . However, data from two small studies link grade 3 pla­
centa prior to 32 weeks with stillbirth and some other adverse
pregnancy outcomes (Chen, 20 1 1 , 20 1 5) .
PLACENTAL TUMORS
• Chorioangioma
These benign tumors have components similar to blood ves­
sels and stroma of the chorionic villus. lso called choran­
giomas, these placental tumors occur with an incidence of
approximately 1 percent (Guschmann, 2003) . In some cases,
fetal-to-maternal hemorrhage across tumor capillaries leads to
elevated levels of maternal serum alpha-fetoprotein (MSAFP) ,
prompting sonographic evaluation. heir characteristic sono­
graphic appearance shows a well-circumscribed, rounded, pre­
dominantly hypoechoic lesion lying near the chorionic plate
and protruding into the amnionic cavity (Fig. 6-4) . Document­
ing increased blood low by color Doppler helps to distinguish
these lesions from other placental masses such as hematoma,
partial hydatidiform mole, teratoma, metastases, and leiomy­
oma (Prapas, 2000) . Although rare, chorangiocarcinoma tumors
clinically mirror chorangiomas (Huang, 20 1 5).
Small chorioangiomas are usually asymptomatic. Large
tumors, typically those measuring >4 em, can create signiicant
arteriovenous shunting within the placenta to cause high-out­
put heart failure, hydrops, and fetal death (l Wattar, 20 1 4) .
Compression o f fetal erythrocytes within tumor vessels can
lead to hemolysis and microangiopathic anemia (Bauer, 1 978) .
Hydramnios, preterm delivery, and fetal-growth restriction are
other sequelae. Rare cases include tumor vessel rupture, hemor­
rhage, and fetal death (Batukan, 200 1 ) . At the other extreme,
rare rumor infarction can lead to symptom reversal (Zalel, 2002) .
115
1 16
P lacentatio n , E m b ryogenesis, a n d Feta l Development
transfusion can treat serious anemia, amnioreduction can tem­
porize hydramnios, and digoxin therapy can assist fetal heart
failure.
• Metastatic Tumors
Maternal malignant tumors rarely metastasize to the placenta.
Of those that do, melanomas, leukemias and lymphomas, and
breast cancer are the most common (Al-Adnani, 2007) . Tumor
cells usually are confined within the intervillous space. As a
result, metastasis to the fetus is uncommon but is most often
seen with melanoma (lexander, 2003) .
Similarly, cases in which fetal malignancy metastasizes to
the placenta are rare (Reif, 20 1 4) . hese are predominantly
fetal neuroectodermal tumors, and only one case in the litera­
ture describes transplantation of tumor to the maternal uterus
(Nath, 1 995) .
AMN IOCHORION
• Chorioamnionitis
Normal genital-tract flora can colonize and infect the mem­
branes, umbilical cord, and eventually the fetus. Bacteria most
commonly ascend after prolonged membrane rupture and dur­
ing labor to cause infection. Organisms initially infect the cho­
rion and adjacent decidua in the area overlying the internal os.
Subsequently, progression leads to full-thickness involvement
of the membranes-chorioamnionitis. Organisms often then
spread along the chorioamnionic surface to colonize and rep­
licate in amnionic luid. Inlammation of the chorionic plate
and of the umbilical cord unisitis-may follow (Kim, 20 1 5 ;
Redline, 20 1 2) .
Most commonly, there i s microscopic o r occult chorioam­
nionitis, which is caused by a wide variety of microorganisms.
his is frequently cited as a possible explanation for many
otherwise unexplained cases of ruptured membranes, preterm
labor, or both as discussed in Chapter 42 (p. 8 1 0) . In some
cases, gross infection is characterized by membrane clouding
and is sometimes accompanied by a foul odor that depends on
bacterial species.
-
F I G U R E 6�4 Placenta l chorioa ngioma. A. Color Doppler i ma g i n g
displays blood flow through a large chorioa ng ioma w i t h i t s border
outli ned by wh ite a rrows. B. Grossly, the chorioa ngioma is a rou nd,
wel l-ci rcu mcised mass protrud i ng from the feta l su rface.
Gray-scale and color Doppler interrogation of the placenta
and amnionic fluid volume are used to identiy these tumors.
Diagnostic tools that can airm associated fetomaternal hem­
orrhage include MSAFP level and Kleihauer-Betke stain. With
fetal concern, echocardiography assesses cardiac function,
whereas middle cerebral artery interrogation is used to identiy
fetal anemia.
Several fetal therapies interfere with the vascular supply to
the tumor and reverse fetal heart failure. At specialized peri­
natal centers, endoscopic laser ablation of feeder vessels to the
tumor is most frequently used and is associated with favorable
fetal outcomes (Hosseinzadeh, 20 1 5) . Of other therapy, fetal
• Other Membrane Abnormalities
Amnion nodosum is a condition characterized by numerous
small, light-tan nodules on the amnion overlying the chorionic
plate. hese may be scraped of the fetal surface and contain
deposits of fetal squames and fibrin that relect prolonged and
severe oligohydramnios (Adeniran, 2007) .
Two notable bandlike structures can be formed by the fetal
membranes. Of these, amnionic band sequence is an anatomical
disruption sequence in which amnion bands tether, constrict,
or amputate fetal parts. Amnionic bands commonly cause
limb-reduction defects, facial clefts, or encephalocele (Barzilay,
20 1 5 ; Guzman-Huerta, 20 1 3) . Umbilical cord compromise is
another sequela (Barros, 20 1 4; Heifetz, 1 984b) . Severe defects
of the spine or ventral wall that accompany amnionic bands
suggest a limb-body wall complex, described in Chapter 1 0
(p. 206) .
Place nta l Abnorm a l ities
Clinically, sonography often irst identiies the sequelae of
this sequence rather than the bands themselves. As with any
fetal anomaly, targeted sonography is indicated. Identiication
of a limb-reduction defect, an encephalocele in an atypical
location, or an extremity with edema or positional deformity
should prompt careful evaluation for amnionic bands.
Management depends on the degree of anatomic deformity.
Fetoscopic laser interruption of the band may be suitable in
highly selected antepartum cases Qavadian, 20 1 3; Mathis, 20 1 5) .
In contrast, a n amnionic sheet i s formed b y normal amnio­
chorion draped over a preexisting uterine synechia. Generally,
these sheets pose little fetal risk, although slightly higher rates of
preterm membrane rupture and placental abruption have been
described (Korbin, 1 998; Nelson, 20 1 0; Tuuli, 20 1 2) .
UMBILICAL CORD
• Length
Most umbilical cords at delivery are 40 to 70 cm long, and very
few measure <30 cm or > 1 00 cm. Cord length is inluenced
positively by both amnionic luid volume and fetal mobility
(Miller, 1 982) . In retrospective studies, short cords have been
linked with congenital malformations and intrapartum distress
(Baergen, 200 1 ; Krakowiak, 2004; Yamamoto, 20 1 6) . Exces­
sively long cords are linked with cord entanglement or prolapse
and with fetal anomalies (Olaya-C, 20 1 5; Rayburn, 1 98 1 ) .
Because antenatal determination o f cord length i s technically
limited, cord diameter has been evaluated as a predictive marker
for fetal outcomes. Some have linked lean cords with poor fetal
growth and large-diameter cords with macrosomia (Proctor,
20 1 3) . However, the clinical utility of this parameter is still
unclear (Barbieri, 2008; Cromi, 2007; Raio, 1 999b, 2003) .
• Coiling
Cord coiling characteristics have been reported but are not
currently part of standard sonographic evaluation. Usually the
umbilical vessels spiral through the cord in a sinistral, that is,
let-twisting direction (Fletcher, 1 993; Lacro, 1 987) . he num­
ber of complete coils per centimeter of cord length is termed
the umbilical coiling index-Uel (Strong, 1 994) . A normal,
antepartum, sonographically derived UCI is 0.4, and this con­
trasts with a normal, postpartum, physically measured value of
0.2 (Sebire, 2007) . UCls < 1 0th percentile are considered hypo­
coile, and those > 90th percentile are hypercoiled. Clinically, the
signiicance of coiling extremes is controversial. Some studies
evaluating large, unselected cohorts ind no associations between
UCI values and poor neonatal outcome Qessop, 20 1 4; Pathak,
20 1 0) . In others, extremes are linked with various adverse out­
comes but most consistently with intrapartum fetal heart rate
abnormalities, preterm labor, or fetal-growth restriction (Chitra,
20 1 2; de Laat, 2006; Predanic, 2005; Rana, 1 995).
• Vessel Number
Counting cord vessel number is a standard component of ana­
tomical evaluation during fetal sonographic examination and
immediately after delivery ( Fig. 6-5) . Embryos initially have two
F I G U R E 6-5 Two u m bil ica l a rteries a re typica l ly documented
sonog ra p h ica l ly in the second trimester. They encircle the fetal
b l adder (asterisk) as extensions of the s u perior ves ical a rteries. I n
t h i s color Doppler sonog ra p h ic i m age, a s i ng le u m bi l ica l a rtery,
s hown in red, ru ns a long the bladder wa l l before joi n i ng the u m b i l­
ica l vei n (blue) i n the cord . Below th is, the two vessels of the cord,
seen as a l a rger red and s m a l ler b l u e circ le, a re a lso seen floati n g in
a cross section of a cord seg ment.
umbilical veins. In the irst trimester, the right vein typically atro­
phies to leave one large vein to accompany the two, thick-walled
umbilical arteries. Four-vessel cords are rare and often associated
with congenital anomalies (Puvabanditsin, 20 1 1 ) . If it is an iso­
lated inding, however, prognosis can be good (Avnet, 20 1 1 ) .
The most common aberration i s that o f a single umbilical
artery (SUA), with a cited incidence of 0.63 percent in liveborn
neonates, 1 .92 percent with perinatal deaths, and 3 percent
in twins (Heifetz, 1 984a) . Fetuses with major malformations
frequently have a single artery. Thus, its identiication often
prompts consideration for targeted sonography and possibly
fetal echocardiography. The most frequent anomalies are car­
diovascular and genitourinary (Hua, 20 1 0; Murphy-Kaulbeck,
20 1 0) . In an anomalous fetus, a single artery greatly increases
the aneuploidy risk, and amniocentesis is recommended (Dag­
klis, 20 1 0; Lubusky, 2007) .
If target sonography inds otherwise normal anatomy, an iso­
lated single artery in an otherwise low-risk pregnancy does not
significantly increase the fetal aneuploidy risk. However, as in
isolated inding, it has been associated with fetal-growth restric­
tion and perinatal death in some but not all studies (Chetty­
John, 20 1 0; Gutvirtz, 20 1 6; Hua, 20 1 0; Murphy-Kaulbeck,
20 1 0; Voskamp, 20 1 3 ) . hus, while clinical monitoring of
growth is reasonable, the value of sonographic surveillance is
unclear.
A rare anomaly is that of a fused umbilical artery with a
shared lumen. It arises from failure of the two arteries to split
during embryological development. The common lumen may
extend through the entire cord, but, if partial, it is typically
found near the placental insertion site (Yamada, 2005) . In one
report, these were associated with a higher incidence of mar­
ginal or velamentous cord insertion, but not congenital fetal
anomalies (Fuj ikura, 2003) .
117
1 18
Pl ace ntation, E m b ryogenesis, a n d Fetal Deve l o pment
Found in most placentas, the Hyrtl anastomosis is a connec­
tion between the two umbilical arteries and lies near the cord
insertion into the placenta. This anastomosis acts as a pressure­
equalizing system between the arteries (Gordon, 2007) . As
a result, redistribution of pressure gradients and blood flow
improves placental perfusion, especially during uterine contrac­
tions or during compression of one umbilical artery. Fetuses
with a single umbilical artery lack this safety valve (Raio,
1 999a, 200 1 ) .
• Remnants and Cysts
Several structures are housed in the umbilical cord during fetal
development, and their remnants may be seen when the mature
cord is viewed transversely. Indeed, J auniaux and colleagues
( 1 989) sectioned 1 000 cords, and in one fourth of the speci­
mens, they found remnants of vitelline duct, allantoic duct, and
embryonic vessels. These were not associated with congenital
malformations or perinatal complications.
Cysts occasionally are found along the course of the cord.
They are designated according to their origin. True cysts are
epithelium-lined remnants of the allantoic or vitelline ducts
and tend to be located closer to the fetal insertion site. In con­
trast, the more common pseudocysts form from local degenera­
tion of Wharton jelly and occur anywhere along the cord. Both
have a similar sonographic appearance. Single umbilical cord
cysts identified in the irst trimester tend to resolve completely,
however, multiple cysts may portend miscarriage or aneuploidy
(Ghezzi, 2003; Hannaford, 20 1 3) . Cysts persisting beyond this
time are associated wi th a risk for structural defects and chro­
mosomal anomalies (Bonilla, 20 1 0; Zangen, 20 1 0) .
• Insertion
The cord normally inserts centrally into the placental disc, but
eccentric, marginal, or velamentous insertions are variants.
Of these, eccentric insertions in general pose no identifiable
fetal risk. Marginal insertion is a common variant-sometimes
referred to as a battledore placenta-in which the cord anchors
at the placental margin. In one population-based study, the
rate was 6 percent in singleton gestations and 1 1 percent in
twins (Ebbing, 20 l 3). This common insertion variant rarely
causes problems, but it and velamentous insertion occasion­
ally result in the cord being pulled of during delivery of the
placenta (Ebbing, 20 1 5; Luo, 20 l 3) . In monochorionic twins,
this insertion may be associated with weight discordance (Kent,
20 1 1 ) .
With velamentous insertion, the umbilical vessels character­
istically travel within the membranes before reaching the pla­
cental margin (Fig. 6-6) The incidence of velamentous insertion
approximates 1 percent but is 6 percent with twins (Ebbing,
20 1 3) . It is more commonly seen with placenta previa (Papin­
niemi, 2007; Raisanen, 20 1 2) . Antenatal diagnosis is possible
sonographically, and with velamentous insertion, cord vessels
are seen traveling along the uterine wall before entering the
placental disc. Clinically, vessels are vulnerable to compression,
which may lead to fetal hypoperfusion and acidemia. Higher
associated rates of low Apgar scores, stillbirth, preterm delivery,
and small for gestational age have been noted (Ebbing, 20 1 7;
Esakof, 20 1 5 ; Heinonen, 1 996; Vahanian, 20 1 5) . Accord­
ingly, monitoring of fetal growth is reasonable either clinically
or sonographically (Vintzileos, 20 1 5) .
Last, with the very uncommon furcate insertion, umbilical
vessels lose their protective Wharton jelly shortly before they
insert. As a result, they are covered only by an amnion sheath
and prone to compression, twisting, and thrombosis.
Va sa Previa
With this condition, vessels travel within the membranes and
overlie the cervical os. here, they can be torn with cervical dila­
tation or membrane rupture, and laceration can lead to rapid fetal
exsanguination. Over the cervix, vessels can also be compressed
by a presenting fetal part. Fortunately, vasa previa is uncom­
mon and has an incidence of 2 to 6 per 1 0,000 pregnancies
F I G U R E 6-6 Vela mentous cord i n sertion. A. The u m b i l ica l cord inserts i nto the membra nes. F rom here, the cord vessels bra nch and a re
s u pported only by mem bra ne u ntil they reach the placental d isc. B. When viewed sonog ra phica l ly a n d u s i n g color Doppler, the cord ves­
sels a ppea r to l ie agai nst the myometri u m as they travel to i n sert m a rg i n a l ly i nto the placenta l d isc, which l ies at the top of this image.
Place nta l A b norm a l ities
(Ruiter, 20 1 6; Sullivan, 20 1 7) . Vasa previa is classiied as type
1 , in which vessels are part of a velamentous cord insertion,
and type 2, in which involved vessels span between portions
of a bilobate or a succenturiate placenta (Catanzarite, 200 1 ) .
Two other risks are conception with i n vitro fertilization and
second-trimester placenta previa, with or without later migra­
tion (Baulies, 2007; Schachter, 2003) .
Compared with intrapartum diagnosis, antepartum diagno­
sis greatly improves the perinatal survival rate, which ranges
from 97 to 1 00 percent (Oyelese, 2004; Rebarber, 20 14;
Swank, 20 1 6) . Thus, vasa previa is ideally identiied early,
although this is not always possible. Clinically, an examiner is
occasionally able to palpate or directly see a tubular fetal ves­
sel in the membranes overlying the presenting part. Efective
screening for vasa previa begins during scheduled midtrimes­
ter sonographic examination. In suspicious cases, transvaginal
sonography is added and shows cord vessels inserting into the
membranes-rather than directly into the placenta-and ves­
sels running above the cervical internal os ( Fig. 6-7) . Routine
color Doppler interrogation of the placental cord insertion site,
particularly in cases of placenta previa or low-lying placenta,
may aid its detection. With this, the vessel waveform relects
the fetal heart rate. In one systematic review, the median pre­
natal detection rate was 93 percent (Ruiter, 20 1 5) .
Once vasa previa i s identiied, subsequent imaging i s rea­
sonable because 6 to 1 7 percent of cases ultimately resolve
(Rebarber, 20 1 5 ; Swank, 20 1 6) . Bed rest apparently has no
added advantage. Antenatal corticosteroids can be provided as
indicated or given prophylactically at 28 to 32 weeks' gestation
to cover possible urgent preterm delivery. Antenatal hospital­
ization may be considered at 30 to 34 weeks to permit sur­
veillance and expedited delivery for labor, bleeding, or rupture
of membranes. Data supporting this is limited, and admission
may best serve women with risk factors that portend early deliv­
ery (Society for Maternal-Fetal Medicine, 20 1 5) . A few cases
F I G U R E 6-7 Vasa previa. U s i n g color Doppler, an u m bi l ica l ves­
sel (red circle) is seen overlyi n g the i nternal os. At the bottom,
the Doppler waveform seen with this vasa previa has the typica l
a ppea ra nce of an u m b i l ical a rtery, with a pu lse rate of 1 4 1 beats
per m i n ute.
of antepartum fetoscopic surgery with vessel laser ablation are
described (Hosseinzadeh, 20 1 5 ; Johnston, 20 1 4) . However,
current practice is early scheduled cesarean delivery. Rob inson
and Grobman (20 1 1 ) performed a decision analysis and recom­
mend elective cesarean delivery at 34 to 35 weeks' gestation
to balance the risks of perinatal exsanguination versus preterm
birth morbidity. he Society for Maternal-Fetal Medicine
(20 1 5) considers planned cesarean delivery at 34 to 37 weeks'
gestation reasonable.
At delivery, the fetus is expeditiously delivered after the hys­
terotomy incision in case a vessel is lacerated during uterine
entry. Delayed cord clamping is not encouraged.
In all pregnancies, otherwise unexplained vaginal bleeding
either antepartum or intrapartum should prompt consideration
of vasa previa and a lacerated fetal vessel. In many cases, bleed­
ing is rapidly fatal, and infant salvage is not possible. With less
hemorrhage, however, it may be possible to distinguish fetal ver­
sus maternal bleeding. Various tests may be used, and each relies
on the increased resistance of fetal hemoglobin to denaturing by
alkaline or acid reagents (Odunsi, 1 996; Oyelese, 1 999) .
• Knots, Strictures, and Loops
Various mechanical abnormalities in the cord can impede blood
low and sometimes cause fetal harm. Of these, true knots are
found in approximately 1 percent of births. hese form from
fetal movement, and associated risks include hydramnios and
diabetes (Hershkovitz, 200 1 ; Raisanen, 20 1 3) . Knots are espe­
cially common and dangerous in monoamnionic twins, which
are discussed in Chapter 45 (p. 874) . When true knots are
associated with singleton fetuses, the stillbirth risk is increased
four- to tenfold (Airas, 2002; S0rnes, 2000) .
Knots can be found incidentally during antepartum sonog­
raphy, and a "hanging noose" sign is suggestive (Ramon y Cajal,
2006) . hree-dimensional and color Doppler aid diagnostic
accuracy (Hasbun, 2007) . With these knots, optimal fetal sur­
veillance is unclear but may include umbilical artery Doppler
velocimetry, nonstress testing, or subjective fetal movement
monitoring (Rodriguez, 20 1 2; Scioscia, 20 1 l ) . Allowing vagi­
nal delivery is suitable, but abnormal intrapartum fetal heart
rate tracings are more often encountered. hat said, cesarean
delivery rates are not increased, and cord blood acid-base values
are usually normal (Airas, 2002; Maher, 1 996) .
In contrast, alse knots form from focal redundancy and fold­
ing of an umbilical cord vessel. hese lack clinical signiicance.
Cord strictures are focal narrowings of the diameter that
usually develop near the fetal cord insertion site (Peng, 2006) .
Characteristic pathological features include an absence of
Wharton jelly and stenosis or obliteration of cord vessels at the
narrow segment (Sun, 1 995). In most instances, the fetus is
stillborn (French, 2005). Even less common is a cord stricture
caused by an amnionic band.
Cord loops are frequently encountered and are caused by
coiling around various fetal parts during movement. A cord
around the neck-a nuchal cord-is common, and vaginal
delivery is suitable. One loop is reported in 20 to 34 percent
of deliveries; two loops in 2 . 5 to 5 percent; and three loops in
0.2 to 0.5 percent (Kan, 1 9 57; S0rnes, 1 995; Spellacy, 1 966) .
119
1 20
P lacentatio n , E m b ryogen esis, a n d Feta l Deve l o pment
During labor, up to 20 percent of fetuses with a nuchal cord
have moderate to severe variable heart rate decelerations, and
these are associated with a lower umbilical artery pH (Hankins,
1 987) . Cords wrapped around the body can have similar efects
(Kobayashi, 20 1 5) . Despite their frequency, nuchal cords are
not associated with greater rates of adverse perinatal outcome
(Henry, 20 1 3; Sheiner, 2006) .
Last, a u nic presentation describes when the umbilical cord
is the presenting part in labor. These are uncommon and most
often are associated with fetal malpresentation (Kinugasa,
2007) . A funic presentation in some cases is identiied with
placental sonography and color low Doppler (Ezra, 2003) .
Overt or occult cord prolapse can complicate labor. hus, once
identiied at term, cesarean delivery is typically recommended.
• Vascular
Cord hematomas are rare and generally follow rupture of an
umbilical vessel, usually the vein, and bleeding into the Whar­
ton jelly. Hematomas have been associated with abnormal
cord length, umbilical vessel aneurysm, trauma, entanglement,
umbilical vessel venipuncture, and funisitis (Gualandri, 2008).
Most are identiied postpartum, but hematomas are recognized
so nographically as hypoechoic masses that lack blood low
(Chou, 2003) . Sequelae include stillbirth or intrapartum abnor­
mal fetal heart rate pattern (Abraham, 20 1 5; Barbati, 2009;
Sepulveda, 2005 ; Towers, 2009) .
Umbilical cord vessel thromboses are rare in utero events and
seldom diagnosed antepartum. Approximately 70 percent are
venous, 20 percent are venous and arterial, and 1 0 percent are
arterial thromboses (Heifetz, 1 988). hese all have high associ­
ated rates of stillbirth, fetal-growth restriction, and intrapartum
fetal distress (Minakami, 200 1 ; Sato, 2006; Shilling, 20 1 4) . If
these are identiied antepartum as hypoechoic masses without
blood low, data from case reports support consideration of
prompt delivery if of viable age (Kanenishi, 20 1 3) .
n umbilical vein varix can complicate either the intraam­
nionic or fetal intraabdominal portion of the umbilical vein.
So no graphically and complemented by color Doppler, rare
intraamnionic varices show cystic dilatation of the umbilical
vein that is contiguous with a normal-caliber portion. Of com­
plications, an intraamnionic varix may compress an adjacent
umbilical artery or can rupture or thrombose. In cases without
these, White and colleagues ( 1 994) recommend fetal surveil­
lance and delivery once fetal maturity is confirmed. However,
data are limited and derived from case reports.
he rare umbilical artey aneuysm is caused by congeni­
tal thinning of the vessel wall with diminished support from
Wharton jelly. Indeed, most form at or near the cord placental
insertion site, where this support is absent. These are associ­
ated with single umbilical artery, trisomy 1 8, amnionic luid
volume extremes, fetal-growth restriction, and stillbirth (Hill,
20 1 0; Vyas, 20 1 6) . At least theoretically, these aneurysms
could cause fetal compromise and death by compression of the
umbilical vein. These aneurysms may appear sonographically as
a cyst with a hyperechoic rim. Within the aneurysm, color low
and spectral Doppler interrogation demonstrate either low­
velocity or turbulent nonpulsatile flow (Olog, 20 1 1 ; Sepulveda,
2003; Shen, 2007b) . Although not codified, management may
include fetal karyotyping, antenatal fetal surveillance, and early
delivery to prevent stillbirth (Doehrman, 20 1 4) .
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third trimesters: signiicance and prenatal approach. Ultrasound Obstet
Gynecol 36(3):296, 20 1 0
1 23
1 24
C H A PT E R 7
E m b ryog e n es i s a n d Feta l
D eve l o p m e n t
GESTATIONAL AGE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 24
EMBRYONIC DEVELOPMENT . . . . . . . . . . . . . . . . . . . . . 1 25
FETAL DEVELOPMENT AND PHYSIOLOGY. . . . . . . . . . . 1 28
ENERGY AND NUTRITION . . . . . . . . . . . . . . . . . . . . . . . . 1 37
PLACENTAL ROLE IN EMBRYOFETAL DEVELOPMENT . . . 1 39
Our knowledge concening thephysioloy oftheoetus has been
markedy enriched during recentyears; nevertheless, when com­
pared with the adult, it oers many points concening which
we are but slighty inormed or prooundy ignorant.
- J . Whitridge Williams ( 1 903)
Since these words were written by Williams in 1 903, great strides
in the understanding of fetal organogenesis and physiology have
been gained. Contemporary obstetrics incorporates physiol­
ogy and pathophysiology of the fetus, its development, and its
environment. An important result is that fetal status has been
elevated to that of a patient who, in large measure, can be given
the same meticulous care that obstetricians provide for gravidas.
In our 2yh edition, the entirety of Section 5 is dedicated to the
fetal patient, as are individual chapters in other sections. Indeed,
virtually every aspect of obstetrics can afect the developing fetus.
GESTATIONAL AGE
Several terms define pregnancy duration and thus fetal age
(Fig. 7-1 ) . Gestational age or menstrual age is the time elapsed
since the first day of the last menstrual period (LMP), a time that
actully precedes conception. This starting time, which is usually
approximately 2 weeks before ovulation and fertilization and nearly
3 weeks before blastocyst implantation, has traditionally been used
because most women know their approximate last period. Embry­
ologists describe embryofetal development in ovuation age, or the
time in days or weeks from ovulation. Another term is postconcep­
tional age, which is nearly identical to ovulation age.
Until recently, clinicians customarily calculated menstrual
age with term pregnancy averaging approximately 280 days,
or 40 weeks between the first day of the LMP and birth. This
corresponds to 9 and 1 13 calendar months. However, men­
strual cycle length variability among women renders many of
these calculations inaccurate. This realization, combined with
the frequent use of first-trimester sonography, has led to more
accurate gestational age determination (Duryea, 20 1 5) . Much
of this change hinges on the accuracy of early sonographic
measurement. As a result, the American College of Obstetri­
cians and Gynecologists, the American Institute of Ultrasound
in Medicine, and the Society for Maternal-Fetal Medicine
(Reddy, 20 1 4) together recommend the following:
1 . First-trimester sonography is the most accurate method to
establish or reairm gestational age.
2. In conceptions achieved with assisted-reproductive technol­
ogy, this gestational age is used.
•
2
I MensesI
•
weeks
3
weeks
IOvulationl Fertilization Ilmplantationl
•
•
}
Gestational age 40 weeks •
Menstrual age (280 days)
Ovulation age
Postconceptional age
F I G U R E 7-1 Termi nology u sed to descri be preg na ncy d u ration.
E m bryogenesis a n d Feta l Devel o p m e n t
3. If available, the gestational ages calculated from the LMP
and from first-trimester sonography are compared, and the
estimated date of coninement (EDC) recorded and dis­
cussed with the patient.
4. The best obstetrical estimate of gestational age at delivery is
recorded on the birth certiicate.
and gestational age. For example, the American College ofObstetri­
cians and Gynecologists (20 1 6) has developed a calculator applica­
tion that incorporates sonographic criteria and the LMP or embryo
transfer date. This is discussed further in Chapter 1 0 (p. 1 83).
he embryofetal crown-rump length in the first trimester
is accurate ±5 to 7 days. hus, if sonographic assessment of
gestational age difers by more than 5 days prior to 9 weeks'
gestation, or by more than 7 days later in the irst trimester, the
estimated delivery date is changed.
The complexity of embryofetal development is almost b eyond
comprehension. Figure 7-2 shows a developmental sequence of
various organ systems. New information regarding organ devel­
opment continues to accrue. For example, imaging techn iques
help unravel the contributions of gene regulation and tissue
interaction to eventual three-dimensional organ morphology
(Anderson, 20 1 6; Mohun, 20 1 1 ) . Others have described the
sequence of gene activation that underlies cardiac development.
EMBRYONIC DEVELOPMENT
• Naegele Rule
An EDC based on LMP can be quickly estimated as follows:
add 7 days to the irst day of the LMP and subtract 3 months.
For example, if the irst day of the LMP was October 5, the
due date is 1 0-05 minus 3 (months) plus 7 (days) = 7-1 2, or
July 12 of the following year. This calculation has been termed
the Naegele rule. The period of gestation can also be divided
into three units of approximately 14 weeks each. These three
trimesters are important obstetrical milestones.
In addition to estimating the EDC with either Naegele rule
or pregnancy "wheels," calculator tools in the electronic medical
record and smartphone applications can provide a calculated EDC
Period:
Weeks
Crown-rump
length (cm)
1 1 2
3
Implantation
I
I
4
I
6
Embryonic Period
(Organogenesis)
5
7
I
Weight (g)
• Zygote and Blastocyst Development
During the irst 2 weeks after ovulation and then fertilization,
the zygote-or preembryo-develops to the blastocyst stage.
The blastocyst implants 6 or 7 days following fertilization . The
5 8-cell blastocyst diferentiates into ive embryo-prod ucing
cells-the inner cel mass-and the remaining 53 cells form pla­
cental trophoblast. Details of implantation and early develop­
ment of the blastocyst and placenta are described in Chapter 5
(p. 87) .
9 1 I 11 21 I I 11 61 I 1 1201 I I 1241 I 1 1281 I I 1321 I 1 1361 138
28
6-7
25
12
16
21
32
2500
110
6 30
1 1 00
320
1 700
8
I
Fetal Period (Growth)
Hemispheres. cerebellum,
Brain
II
Neural tube
Face
Ears
I
Lungs
I
I
Transverse septum, diaphragm
Tracheoesophageal septum, bronchi, lobes
I
Heart
:
Canals, ccchlea. inner ears. ossicles
I
Primitive tube, great vessels, valves. chambers
I
I
I
I
Pinnae
Diaphragm
I
OptiC cups, lens, optic nerves, eyelids
I
!
Temporal lobe, sulci, gyri, cellular migration, myelinization
I
Lips , tongue, palate, cavitatio
I
Eyes
r, fusion
ventricles, choroid plexus
I
I
I
�
I
l
I
Canal
Brows
I
I
I
Pinnae
kuli
I
Eyes op�n
I
Terminal sacs
1
I
I
!
Abdominc I wall,
Intestines
Foregut, liver, pancreas, midgut
I
Urinary tract
Genitalia
Mesonephric duct
I
I
I
gut rota ion
I
Metanephric duct collecting sytem
I
I
Axial skeleton
Limbs
Skin
I
Genital folds, phallus, labioscrotal swelling
I
I
I
! Peni
I
I
I
, urethra, scrotum
� Clit( ris, labia
Vertebral cartilage, ossification centers
Buds, rays, webs, separate digits
I
I
I
I
I
I
Fingernails
I
I
I
I
Glomeruli
:
!I
I
I
!
:
Vernix
I
I
i
Lanugo h a i r
I
I
F I G U R E 7-2 Embryofeta l developm ent according to gestational age determ ined by the first day of the last menses. Times are approxi mate.
1 25
1 26
Placentation, E m b ryoge nesis, a n d Feta l Development
-- Yolk
A
�
'I
sac
.
Yolk ­
sac
Embryo
Developing
neural groove
- Amnion
Developi ng villi
c
B
F I G U R E 7-3 Early h u ma n e m b ryos. Ovu l ation ages: A. 1 9 days (presom ite). B. 2 1 days (7 somites). C. 22 days ( 1 7 somites). (After d rawi ngs
a n d models i n the Carneg ie I n stitute.)
• Embryonic Period
gonadotropin (hCG) become positive by this time. As shown
in Figure 7-3, the body stalk is now diferentiated. There are
villous cores in which angioblastic chorionic mesoderm can be
distinguished and a true intervillous space that contains mater­
nal blood.
During the third week, fetal blood vessels in the chorionic
villi appear. In the fourth week, a cardiovascular system has
formed (Fig. 7-4) . hereby, a true circulation is established
he conceptus is termed an embryo at the beginning of the
third week after ovulation and fertilization. Primitive chorionic
villi form, and this coincides with the expected day of menses.
he embryonic period, during which time organogenesis takes
place, lasts 6 weeks. It begins the third week from the LMP
through the eighth week. The embryonic disc is well deined,
and most pregnancy tests that measure human chorionic
- Neural
...-Rostral
Neural fold
.--Neural
rr---Rostral
groove
neuropore
--Somites
.-- - Neural
Somites
---Caudal neuropore
f..
-- _ Caudal
,.--
___
Th i rd
� branchial arch
-- "
�
arch
---
Heart
prom i nence
---:
c
D
neuropore
pit
-:- Lens
arch
Mandibular
arch
� Arm bud
Som ites
tube
---Otic
Otic pit
__ Hyoid
Y --- Mandibular
fold
neuropore
placode
Arm bud
Leg bud
E
--� Leg
bud
FIGURE 7-4 Th ree- to four-week-old embryos. A, B. Dorsal views of embryos d u ri ng 22 to 23 days of development showi ng 8 a nd 1 2 som ites,
respectively. (-E. Latera l views of embryos d u ring 24 to 28 days, showin g 1 6, 27, and 33 somites, respectively. (Redrawn from Moore KL: The
Developing H u man: Clin ically Oriented E m b ryology, 4th ed. Philadel p h ia, Sa u nders, 1 988.)
E m bryogenesis a n d Feta l Develop m e nt
FIGURE 7-5 E m byro photo g ra phs. A. Dorsa l view of a n embryo at 24 to 26 days a nd correspon d i ng to F ig u re 7-4C. B. Lateral view of a n
em bryo at 2 8 days a n d correspond i n g to Fig u re 7-40. C . Latera l view o f e m b ryofetus at 5 6 days, which m a rks the end o f the e m bryo n i c
period a n d t h e beg i n n ing of t h e feta l period. The l iver is with i n the wh ite, halo circle. (From Werth B , Tsiara s A : F rom Conceptio n t o Bi rth:
A Life U nfolds. New York, Dou bleday, 2002.)
both within the embryo and between the embryo and the cho­
rionic villi. Partitioning of the primitive heart begins. Also in
the fourth week, the neural plate forms, and it subsequently
folds to form the neural tube. By the end of the ifth men­
strual week, the chorionic sac measures approximately 1 cm
in diameter. he embryo is 3 mm long and can be measured
sonographically. Arm and leg buds have developed, and the
amnion is beginning to ensheathe the body stalk, which there­
after becomes the umbilical cord. At the end of the sixth week,
FIGURE 7-6 A. Th is image of a 6-week, 4-day embryo depicts
measurement of the crown-ru m p l e n gth, which is 7.4 mm at this
gestational age. B. Despite the ea rly gestational age, M-mode
imaging rea d i ly demonstrates e m b ryonic cardiac activity. The hea rt
rate in this i mage is 1 24 beats per m i n ute.
the embryo measures approximately 9 mm long, and the neural
tube has closed (Fig. 7-5) . Cardiac motion is almost always dis­
cern able sonographically (Fig. 7-6) . The cranial end of the neu­
ral tube closes by 38 days from the LMP, and the caudal end
closes by 40 days. Thus, the neural tube has closed by the end of
the sixth week. And by the end of the eighth week, the crown­
rump length approximates 22 mm. Fingers and toes are present,
and the arms bend at the elbows. The upper lip is complete, and
the external ears form definitive elevations on either side of the
1 27
1 28
P l acentation, E m b ryogenes i s, and Feta l Deve lop ment
head. hree-dimensional images and videos of human embryos
from the MultiDimensional H uman Embryo project are found
at: http://embryo.soad. umich.edu/index.html.
F ETAL DEVELOPMENT A N D PHYSIOLOGY
• Fetal Period Epochs
Transition from the embryonic period to the fetal period occurs
at 7 weeks after fertilization, corresponding to 9 weeks after
onset of the last menses. At this time, the fetus approximates
24 mm in length, most organ systems have developed, and the
fetus enters a period of growth and maturation. These phases
are outlined in Figure 7-2.
1 2 G estational Wee ks
The uterus usually is just palpable above the symphysis pubis.
Fetal growth is rapid, and the fetal crown-rump length is 5 to 6
cm (Fig. 7-7) . Centers of ossiication have appeared in most fetal
bones, and the fingers and toes have become diferentiated. Skin
and nails develop, and scattered rudiments of hair appear. he
external genitalia are beginning to show deinitive signs of male or
female gender. he fetus begins to make spontaneous movements.
1 6 Gestationa l Weeks
Fetal growth slows at this time. The crown-rump length is 1 2
cm, and the fetal weight approximates 1 50 g (Hadlock, 1 99 1 ) .
Practically speaing, the sonographic crown-rump length is not
measured beyond 1 3 weeks, which corresponds to approxi­
mately 8 .4 cm. Instead, biparietal diameter, head circumference,
abdominal circumference, and femur length are measured. Fetal
weight in the second and third trimesters is estimated from a
combination of these measurements (Chap. 1 0, p. 1 84) .
Eye movements begin at 1 6 to 1 8 weeks, coinciding with
midbrain maturation. By 1 8 weeks in the female fetus, the
uterus is formed and vaginal canalization begins. By 20 weeks
in the male, testicles start to descend.
20 Gestationa l Weeks
This is the midpoint of pregnancy as estimated from the LMP.
The fetus now weighs somewhat more than 300 g, and weight
increases substantially in a linear manner. From this point
onward, the fetus moves approximately every minute and is
active 1 0 to 30 percent of the day (DiPietro, 2005) . Brown
fat forms, and the fetal skin becomes less transparent. Downy
lanugo covers its entire body, and some scalp hair can be seen.
Cochlear function develops between 22 and 25 weeks, and its
maturation continues for 6 months after delivery.
24 Gestational Weeks
The fetus now weighs almost 700 g (Duryea, 20 1 4) . he skin is
characteristically wrinkled, and fat deposition begins. The head
is still comparatively large, and eyebrows and eyelashes are usu­
ally recognizable. By 24 weeks, the secretory type II pneumo­
cytes have initiated surfactant secretion (Chap. 32, p. 607) . The
canalicular period of lung development, during which the bron­
chi and bronchioles enlarge and alveolar ducts develop, is nearly
completed. Despite this, a fetus born at this time will attempt
to breathe, but many will die because the terminal sacs, required
for gas exchange, have not yet formed. The overall survival rate
at 24 weeks is barely above 50 percent, and only approximately
30 percent survive without severe morbidity (Rysavy, 20 1 5) . By
26 weeks, the eyes open. Nociceptors are present over all the
body, and the neural pain system is developed (Kadic, 20 1 2) .
The fetal liver and spleen are important sites for hemopoiesis.
28 Gestationa l Weeks
The crown-rump length approximates 25 cm, and the fetus
weighs about 1 1 00 g. The thin skin is red and covered with
vernix caseosa. The pupillary membrane has j ust disappeared
from the eyes. Isolated eye blinking peaks at 28 weeks. The
bone marrow becomes the major site of hemopoiesis. he oth­
erwise normal neonate born at this age has a 90-percent chance
of survival . without physical or neurological impairment.
32 a n d 36 Gestational Wee ks
At 32 weeks, the fetus has attained a crown-rump length
approximating 28 cm and a weight of about 1 800 g. he skin
surface is still red and wrinkled. In contrast, by 36 weeks, the
fetal crown-rump length averages about 32 cm, and the weight
approximates 2800 g (Duryea, 20 1 4) . Because of subcutaneous
fat deposition, the body has become more rotund, and the pre­
vious wrinkled facies is now fuller. Normal fetuses have nearly
1 00-percent survival rate.
40 Gestational Weeks
This is considered term, and the fetus is now fully developed.
The average crown-rump length measures about 36 cm, and the
average weight approximates 3 500 g.
• Central Nervous System Development
F I G U R E 7-7 This image of a 1 2-week, 3-day e m b ryo depicts mea­
s u rement of the crown-ru m p length. The feta l profi le, cra n i u m , a n d
a h a n d a n d foot a re a l so visible i n this i mage.
Bra i n Development
The cranial end of the neural tube closes by 3 8 days from
the LMP , and the caudal end closes by 40 days. Hence, folic
E m b ryogenesis a nd Feta l Develop m ent
acid supplementation to prevent neural-tube defects must
be in place before this point to be eicacious (Chap. 9,
p . 1 69 ) . The walls of the neural tube form the brain and
spinal cord. The lumen becomes the ventricular system of
the brain and the central canal of the spinal cord. D uring
the sixth week, the cranial end of the neural tube forms three
primary vesicles. In the seventh week, five secondary vesicles
develop : the telencephalon-future cerebral hemispheres;
diencephalon-thalami ; mesencephalon-midbrain; met­
encephalon-pons and cerebellum; and myelencephalon­
medulla. Meanwhile, lexures develop and fold the brain into
its typical configuration. The end of the embryonic period
signiies completion of primary and secondary neuralization.
At 3 to 4 months' gestation, neuronal proleration peaks.
As expected, disorders in this cerebral development phase pro­
foundly worsen function (Volpe, 2008) . Neuronal migration
occurs almost simultaneously and peaks at 3 to 5 months. This
process is characterized by movement of millions of neuronal
cells from their ventricular and subventricular zones to areas of
the brain in which they reside for life (Fig. 7-8) . U pregulation
of gene expression for neuronal migration has been described
(Iruretagoyena, 20 1 4) . Noninvasive methods to study fetal
neurodevelopment have also been reported (Goetzl, 20 1 6) .
As gestation progresses, the fetal brain appearance steadily
changes. Thus, it is possible to identiY fetal age from its exter­
nal appearance (Volpe, 2008) . Neuronal proliferation and
migration proceed along with gyral growth and maturation (see
Fig. 7-8). Sequential maturation studies by Manganaro (2007)
and Dubois (20 1 4) and their colleagues have characterized the
developing fetal brain image using magnetic resonance (MR)
imaging. Other recent investigations that also used MR imag­
ing have quantiied development of subcortical brain structures
from 1 2 to 22 weeks (Meng, 20 1 2) .
Myelination o f the ventral roots o f the cerebrospinal nerves
and brainstem begins at approximately 6 months, but most
A
B
c
�.
. �.
'''
FIGURE 7-8 Neuro n a l prol iferation a n d migration a re com p l ete at
20 to 24 weeks. During the second h a lf of gestation, organ ization a l
events proceed with gyral formation a nd proliferation, d ife rentia­
tion, and m i g ration of cel l u l a r elements. Approximate gestation a l
ages a re shown. A . 20 weeks. B . 35 weeks. C. 4 0 weeks.
myelination progresses after birth. This lack of myeli n and
incomplete skull ossiication permit fetal brain structure to be
seen sonographically throughout gestation.
S p i n a l Cord
Whereas the superior two thirds of the neural tube give rise
to the brain, the inferior third forms the spinal cord. In the
embryo, the spinal cord extends along the entire vertebral
column length, but after that it lags behind vertebral growth.
Ossiication of the entire sacrum is visible sonographically by
approximately 2 1 weeks (Chap. 1 0, p. 1 9 1 ) . By 24 weeks, the
spinal cord extends to S I at birth to L3, and in the adult to LI .
'
Spinal cord myelination begins at midgestation and con tinues
through the irst year of life. Synaptic function is suiciently
developed by the eighth week to demonstrate flexion of the
neck and trunk (Temiras, 1 968) . During the third trimester,
integration of nervous and muscular function proceeds rapidly.
• Cardiovascular System
The embryology of the heart is complex. At its earliest stages of
formation, the fetal heart undergoes molecular programming,
and more than a hundred genes and molecular factors are inte­
gral to its morphogenesis. To summarize, the straight cardiac
tube is formed by the 23rd day during an intricate morphoge­
netic sequence, during which each segment arises at a unique
time. The tube then undergoes looping, and the chambers then
fuse and form septa (Manner, 2009) . The valves develop, and
the aortic arch forms by vasculogenesis. For a complete descrip­
tion, refer to Chapter 9 in Hurst s he Heart (Keller, 20 1 3) .
Feta l C i rcu lation
his unique circulation is substantially diferent from that of
the adult and functions until birth, when it changes dramati­
cally. For example, because fetal blood does not need to enter
the pulmonary vasculature to be oxygenated, most of the right
ventricular output bypasses the lungs. In addition, the fetal
heart chambers work in parallel, not in series, which efectively
supplies the brain and heart with more highly oxygenated
blood than the rest of the body.
Oxygen and nutrient materials required for fetal growth
and maturation are delivered from the placenta by the single
umbilical vein (Fig. 7-9) . The vein then divides into the ductus
venosus and the portal sinus. The ductus venosus is the major
branch of the umbilical vein and traverses the liver to enter the
inferior vena cava directly. Because it does not supply oxygen to
the intervening tissues, it carries well-oxygenated blood directly
to the heart. In contrast, the portal sinus carries blood to the
hepatic veins primarily on the left side of the liver, and oxygen
is extracted. The relatively deoxygenated blood from the liver
then lows back into the inferior vena cava, which also receives
more deoxygenated blood returning from the lower body. Blood
flowing to the fetal heart from the inferior vena cava, therefore,
consists of an admixture of arterial-like blood that passes directly
through the ductus venosus and less well-oxygenated blood that
returns from most of the veins below the level of the diaphragm.
The oxygen content of blood delivered to the heart from the
inferior vena cava is thus lower than that leaving the placenta.
1 29
1 30
P lacentati on, E m bryog enesis, a n d Feta l Deve l o p ment
Ductus
/
/
Foramen
ovale
Aorta
Umbilical v.
Hypogastric
aa.
_
_
Oxygenated
Mixed
Deoxygenated
F I G U R E 7-9 The i ntricate natu re of the feta l circ u l ation is evident. The deg ree of blood oxygenation in va rious vesse l s d iffers apprecia bly
from t hat i n the postnata l state. aa a rteries; LA left atri u m; LV left ventricle; RA right atri u m; RV right ventricle; v vei n.
=
=
=
As discussed, the ventricles of the fetal heart work in paral­
lel, not in series. Well-oxygenated blood enters the left ven­
tricle, which supplies the heart and brain, and less oxygenated
blood enters the right ventricle, which supplies the rest of the
body. These two separate circulations are maintained by the
right atrial structure, which efectively directs entering blood
to either the left atrium or the right ventricle, depending on
its oxygen content. his separation of blood according to its
=
=
=
oxygen content is aided by the pattern of blood flow in the
inferior vena cava. The well-oxygenated blood tends to course
along the medial aspect of the inferior vena cava and the less
oxygenated blood flows along the lateral vessel wall. This aids
their shunting into opposite sides of the heart. Once this blood
enters the right atrium, the configuration of the upper inter­
atrial septum-the crista dividens-preferentially shunts the
well-oxygenated blood from the medial side of the inferior
E m b ryogenesis and Feta l Deve l o pment
vena cava and the ductus venosus through the foramen ovale
into the left heart and then to the heart and brain (Dawes,
1 962) . After these tissues have extracted needed oxygen, the
resulting less oxygenated blood returns to the right atrium
through the superior vena cava.
The less oxygenated blood coursing along the lateral
wall of the inferior vena cava enters the right atrium and is
deflected through the tricuspid valve to the right ventricle.
The superior vena cava courses inferiorly and anteriorly as
it enters the right atrium, ensuring that less well-oxygenated
blood returning from the brain and upper body also will be
shunted directly to the right ventricle. Similarly, the ostium
of the coronary sinus lies j ust superior to the tricuspid valve
so that less oxygenated blood from the heart also returns to
the right ventricle. As a result of this blood flow pattern,
blood in the right ventricle is 1 5 to 20 percent less saturated
than blood in the left ventricle.
lmost 90 percent of blood exiting the right ventricle is
shunted through the ductus arteriosus to the descending aorta.
High pulmonary vascular resistance and comparatively lower
resistance in the ductus arteriosus and the umbilical-placental
vasculature ensure that only about 8 percent of right ventricular
output goes to the lungs (Fineman, 20 1 4) . Thus, one third of
the blood passing through the ductus arteriosus is delivered to
the body. The remaining right ventricular output returns to the
placenta through the two hypogastric arteries. These two arter­
ies course from the level of the bladder along the abdominal
wall to the umbilical ring and into the cord as the umbilical
arteries. In the placenta, this blood picks up oxygen and other
nutrients and is recirculated through the umbilical vein.
Ci rc u l atory C h a n g es at B i rth
After birth, the umbilical vessels, ductus arteriosus, foramen
ovale, and ductus venosus normally constrict or collapse. With
the functional closure of the ductus arteriosus and the expan­
sion of the lungs, blood leaving the right ventricle preferentially
enters the pulmonary vasculature to become oxygenated before
it returns to the left heart (Hillman, 20 1 2) . Virtually instanta­
neously, the ventricles, which had worked in parallel in fetal
life, now efectively work in series. The more distal portions
of the hypogastric arteries undergo atrophy and obliteration
within 3 to 4 days after birth. hese become the umbilical liga­
ments, whereas the intraabdominal remnants of the umbilical
vein form the ligamentum teres. The ductus venosus constricts
by 1 0 to 96 hours after birth and is anatomically closed by 2
to 3 weeks. This ultimately forms the ligamentum venosum
(Fineman, 20 1 4) .
Feto pl a centa l Blood Vo l u me
Although precise measurements of human fetoplacental blood
volume are lacking, Usher and associates ( 1 963) reported values
in term normal newborns to average 78 mLlkg when immedi­
ate cord clamping was conducted. Gruenwald ( 1 967) found
the fetal blood volume contained in the placenta after prompt
cord clamping to average 45 mLlkg of fetal weight. Thus, feto­
placental blood volume at term is approximately 1 2 5 mLlkg of
fetal weight. This is important when assessing the magnitude of
fetomaternal hemorrhage as discussed in Chapter 1 5 (p. 307) .
• Hemopoiesis
In the early embryo, h emopoiesis is demonstrable first in the
yolk sac, followed by the liver, and inally spleen and bone
marrow. Both myeloid and erythroid cells are continually pro­
duced by progenitors that are from h ematopoietic stem cells
(Golub, 20 1 3; Heinig, 20 1 5) . The first erythrocytes released
into the fetal circulation are nucleated and macrocytic. The
mean cell volume is at least 1 80 L in the embryo and decreases
to 1 05 to 1 1 5 L at term. The erythrocytes of aneuploid fetuses
generally do not undergo this maturation and maintain high
mean cell volumes- 1 30 L on average (Sipes, 1 99 1 ) . As fetal
development progresses, more and more of the circulating
erythrocytes are smaller and nonnucleated. With fetal growth,
both the blood volume in the common fetoplacental circu­
lation and hemoglobin concentration increase. As shown in
Figure 7- 1 0, fetal hemoglobin concentrations rise across preg­
nancy. The Society for Maternal-Fetal Medicine (20 1 5) rec­
ommends a cutof hematocrit value of 30 percent to define
anemia.
Because of their large size, fetal erythrocytes have a short
life span, which progressively lengthens to approximately 90
days at term (Pearson, 1 966). As a consequence, red blood cell
production rises. Reticulocytes are initially present at high lev­
els, but decrease to 4 to 5 percent of the total at term. Fetal
erythrocytes difer structurally and metabolically from those
in the adult (Baron, 20 1 2) . They are more deformable, which
serves to ofset their higher viscosity. They also contain several
enzymes with appreciably diferent activities.
Erythropoiesis is controlled primarily by fetal erythro­
poietin because maternal erythropoietin does not cross the
placenta. Fetal hormone production is influenced by testos­
terone, estrogen, prostaglandins, thyroid hormone, and lipo­
proteins (Stockman, 1 992). Serum erythropoietin levels rise
with fetal maturity. Although the exact production site is dis­
puted, the fetal liver appears to be an important source until
renal production begins. There is a close correlation between
the erythropoietin concentration in amnionic fl u id and that
in umbilical venous blood obtained by cordocentesis. After
birth, erythropoietin normally may not be detectable for up
to 3 months.
In contrast, platelet production reaches stable levels by mid­
pregnancy, although there is some variation across gestation
(Fig. 7- 1 1 ) . The fetal and neonatal platelet count is subject to
various agents as discussed in Chapter 1 5 (p. 307) .
Feta l H e m o g l o b i n
This tetrameric protein is composed of two copies of two
diferent peptide chains, which determine the type of hemo­
globin produced. Normal adult hemoglobin A is made of
a and 3 chains. During embryonic and fetal life, various
a and 3 chain precursors are produced. This results in the
serial production of several diferent embryonic hemoglobins.
Genes for 3-type chains are on chromosome 1 1 , and those
for a-type chains on chromosome 1 6. Each of these genes is
turned on and then of during fetal life, until a and 3 genes,
which direct the production of adult hemoglobin A, are per­
manently activated.
131
1 32
P l acentation, E m b ryogenesis, a nd Feta l Deve l o pm e nt
18
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Moderate anemia
32
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34
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Gestational age (weeks)
F I G U R E 7- 1 0 Relations h i p between feta l hemog lobin across gestational age. B l ue d ots ind icate fetuses with hyd rops. (Reprod uced with
perm ission from Mari G, Deter R L, Ca rpenter R L, et a l : Noni nvasive d iag nosis by Doppler u ltrasonog ra phy of feta l a n e m ia due to maternal
red-ce l l a l lo i m m u n ization. Col l a borative Gro u p for Doppler Assessment of the Blood Velocity in Anemic Fetuses (Level I I-I), N Eng l J Med
2000 J a n 6;342( 1 ):9- 1 4.)
The timing of production of each of these early hemoglobins
corresponds to the site of hemoglobin production. Fetal blood
is fi r st produced in the yolk sac, where hemoglobins Gower 1 ,
Gower 2, and Portland are made. Erythropoiesis then moves to
the liver, where fetal hemoglobin F is produced. When hemopoi­
esis finally moves to the bone marrow, adult-type hemoglobin
A appears in fetal red blood cells and is present in progressively
greater amounts as the fetus matures (Pataryas, 1 972) .
he final adult version of the . chain is produced exclu­
sively by 6 weeks. Mter this, there are no functional alternative
400,000
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24 26 28 30 3 2 3 4 36 38 40 4 2
G estational a g e (weeks)
FIGURE 7-1 1 Platelet cou nts by gestational age obta i ned the first
day of l ife. Mea n va l ues a n d 5th a nd 95th percenti les a re shown.
(Data from C h ristensen RD, Hen ry E, Antonio DV: Throm bocytosis
and throm bocytopenia in the N ICU: incidence, mechanisms and
treatments, J Matern Feta l Neonata l Med 201 2 Oct;25 SuppI 4: 1 5- 1 7)
versions. If an a-gene mutation or deletion occurs, no alternate
a-type chain can be substituted to form functional hemoglo­
bin. In contrast, at least two versions of the � chain-6 and
,-remain in production throughout fetal life and beyond. In
the case of a �-gene mutation or deletion, these two other ver­
sions of the � chain often continue to be produced, resulting
in hemoglobin A2 or hemoglobin F, which substitute for the
abnormal or missing hemoglobin.
Genes are turned of by methylation of their control region,
which is discussed in Chapter 1 3 (p. 267). In some situations,
methylation does not occur. For example, in newborns of diabetic
women, hemoglobin F may persist due to hypomethylation of
the , gene (Perrine, 1 988). With sickle cell anemia, the , gene
remains unmethylated, and large quantities of fetal hemoglobin
continue to be produced. s discussed in Chapter 56 (p. 1 08 1 ),
elevated hemoglobin F levels are associated with fewer sickle-cell
disease symptoms, and pharmacological modiication of these lev­
els by hemoglobin F-inducing drugs is one approach to treatment.
As discussed on page 1 40, there is a functional diference
between hemoglobins A and F. At any given oxygen tension and
at identical pH, fetal erythrocytes that contain mostly hemoglo­
bin F bind more oxygen than do those that contain nearly all
hemoglobin A (Fig. 47-2, p. 920) . his is because hemoglobin
A binds 2,3-diphosphoglycerate (2,3-DPG) more avidly than
does hemoglobin F, thus lowering the ainity of hemoglobin
A for oxygen. During pregnancy, maternal 2,3-DPG levels are
greater, and because fetal erythrocytes have lower concentra­
tions of 2,3-DPG, the latter has increased oxygen ainity.
he amount of hemoglobin F in fetal erythrocytes begins
to decrease in the last weeks of pregnancy. At term, approxi­
mately three fourths of total hemoglobin levels are hemoglobin
E m b ryogenesis a n d Feta l Development
F. During the irst 6 to 1 2 months of life, the hemoglobin F
proportion continues to decline and eventually reaches the low
levels found in adult erythrocytes.
Coa g u lation Factors
With the exception of fi b rinogen, there are no embryonic
forms of the various hemostatic proteins. he fetus starts pro­
ducing normal, adult-type procoagulant, ibrinolytic, and anti­
coagulant proteins by 1 2 weeks. Because they do not cross the
placenta, their concentrations at birth are markedly below the
levels that develop within a few weeks of life (Corrigan, 1 992) .
In normal neonates, the levels of factors II, VII, IX, X, XI,
and of protein S, protein C, antithrombin, and plasminogen
all approximate 50 percent of adult levels. In contrast, levels of
factors V, VIII, XIII, and ibrinogen are closer to adult values
(Saracco, 2009) . Without prophylactic treatment, the levels
of vitamin K-dependent coagulation factors usually decrease
even further during the irst few days after birth. his decline is
ampliied in breastfed infants and may lead to newborn hemor­
rhage (Chap. 33, p. 626).
Fetal ibrinogen, which appears as early as 5 weeks, has the
same amino acid composition as adult ibrinogen, however,
it has diferent properties (Klagsbrun, 1 988). It forms a less
compressible clot, and the ibrin monomer has a lower degree
of aggregation (Heimark, 1 988) . Although plasma ibrinogen
levels at birth are less than those in nonpregnant adults, the
protein is functionally more active than adult ibrinogen (Ign­
jatovic, 20 1 1 ) .
Levels o f functional fetal factor XIII-ibrin stabilizing fac­
tor-are signiicantly reduced compared with those in adults
(Henriksson, 1 974) . Nielsen ( 1 969) described low levels of
plasminogen and elevated ibrinolytic activity in cord plasma
compared with that of maternal plasma. Platelet counts in
cord blood are in the normal range for nonpregnant adults (see
Fig. 7- 1 1 ) .
Despite this relative reduction i n procoagulants, the fetus
appears to be protected from hemorrhage, and fetal bleeding is
rare. Even after invasive fetal procedures such as cordocentesis,
excessive bleeding is uncommon. Ney and coworkers ( 1 989)
have shown that amnionic luid thromboplastins and a factor(s)
in Wharton jelly combine to aid coagulation at the umbilical
cord puncture site.
Various thrombophilias may cause thromboses and preg­
nancy complications in adults (Chap. 52, p. 1 008). If the fetus
inherits one of these mutations, thrombosis and infarction can
develop in the placenta or fetal organs. his is usually seen with
homozygous inheritance. One example is homozygous protein
C mutation, which causes purpura fulminans.
Plasma Prote i n s
Liver enzymes and other plasma proteins are produced b y the
fetus, and these levels do not correlate with maternal levels
(Weiner, 1 992) . Concentrations of plasma proteins, which
include albumin, lactic dehydrogenase, aspartate aminotrans­
ferase, 1-glutamyl transpeptidase, and alanine transferase, all
rise. Conversely, prealbumin levels decline with gestational age
(Fryer, 1 993) . At birth, mean total plasma protein and albumin
concentrations in fetal blood are similar to maternal levels. This
is important because albumin binds unconjugated bilirubin to
prevent kernicterus in the newborn (Chap. 33, p. 626) .
• Respiratory System
Lung maturation and biochemical indices of functional fetal
lung maturity are important predictors of early neonatal out­
come. Morphological or functional immaturity at birth leads
to the development of the respiratoy distress syndrome (Chap.
34, p. 636) . A suicient amount of surface-active materials­
collectively referred to as suactant-in the amnionic fl u id is
evidence of fetal lung maturity. As Liggins ( 1 994) emphasized,
however, the structural and morphological maturation of fetal
lung also is extraordinarily important to proper lung function.
A n ato m ic a l Maturation
The limits of viability appear to be determined by the usual
process of pulmonary growth. Like the branching of a tree,
lung development proceeds along an established timetable that
apparently cannot be hastened by antenatal or neonatal ther­
apy. Within this framework, four essential lung development
stages are described by Moore (2000) . First, the pseudoglan­
dular stage entails growth of the intrasegmental bronchial tree
between the 5 th and 1 7th weeks. During this period, the lung
looks microscopically like a gland. Second, during the canalicu­
lar stage, from 1 6 to 25 weeks, the bronchial cartilage plates
extend peripherally. Each terminal bronchiole gives rise to sev­
eral respiratory bronchioles, and each of these in turn divides
into multiple saccular ducts. Third, the terminal sac stage begins
after 25 weeks. During this stage, alveoli give rise to primitive
pulmonary alveoli, that is, the terminal sacs. Simultaneously,
an extracellular matrix develops from proximal to distal lung
segments until term. Finally, the alveolar stage begins during
the late fetal period and continues well into childhood. An
extensive capillary network is built, the lymph system forms,
and type II pneumocytes begin to produce surfactant. At birth,
only approximately 1 5 percent of the adult number of alveoli is
present. hus, the lung continues to grow, adding more alveoli
for up to 8 years.
Various insults can upset this process, and their timing
determines the sequelae. One example is fetal renal agenesis, in
which amnionic luid is absent at the beginning of lung growth,
and major defects occur in all four developmental stages. In
another instance, the fetus with membrane rupture and sub­
sequent oligohydramnios before 20 weeks usually exhibits
nearly normal bronchial branching and cartilage development
but has immature alveoli. In contrast, membrane rupture after
24 weeks may have minimal long-term efect on pulmonary
structure. In another example, various growth factors are
expressed abnormally in the fetus with a diaphragmatic her­
nia (Candilira, 20 1 5) . Finally, vitamin D is thought to be
important for several aspects of lung development (Hart, 20 1 5 ;
Lykkedegn, 20 1 5).
Pul m o n a ry S u rfactant
After the irst breath, the terminal sacs must remain expanded
despite the pressure imparted by the tissue-to-air interface, and
surfactant keeps them from collapsing. Surfactant is formed
1 33
1 34
P l acentation, E m b ryog enesis, a n d Feta l Deve l opment
in type II pneumonocytes that line the alveoli. These cells are
characterized by multivesicular bodies that produce the lamel­
lar bodies in which surfactant is assembled. During late fetal
life, at a time when the alveolus is characterized by a water­
to-tissue interface, the intact lamellar bodies are secreted from
the lung and swept into the amnionic fluid during respiratory­
like movements that are termed fetal breathing. At birth, with
the first breath, an air-to-tissue interface is established in the
lung alveolus. Surfactant uncoils from the lamellar bodies and
spreads to line the alveolus to prevent alveolar collapse during
expiration. hus, the fetal lungs' capacity to produce surfactant
establishes lung maturity.
Su rfactant Com position. Gluck ( 1 972) and Hallman ( 1 976)
and their coworkers approximated that 90 percent of surfac­
tant's dry weight is lipid, speciically glycerophospholipids.
Proteins account for the other 1 0 percent. Nearly 80 percent of
the glycerophospholipids are phosphatidylcholines (lecithins) .
The principal active component that constitutes half of surfac­
tant is a speciic lecithin, which is dipalmitoylphosphatidylcho­
line (DPPC or PC) . Phosphatidylglycerol (PG) accounts for
another 8 to 1 5 percent. Its precise role is unclear because new­
borns without PG usually do well. he other major constituent
is phosphatidylinositol (PI) . The relative contributions of each
component are shown in Figure 7- 1 2.
Su rfactant Synthesis. Biosynthesis takes place in the type II
pneumocytes. he apoproteins are produced in the endoplas­
mic reticulum, and the glycerophospholipids are synthesized
by cooperative interactions of several cellular organelles. Phos­
pholipid is the primary surface tension-lowering component of
surfactant, whereas the apoproteins aid the forming and reform­
ing of a surface ilm.
The major apoprotein is surfactant A (SP-A) , which is a gly­
coprotein with a molecular weight of 28,000 to 3 5 ,000 Da
(Whitsett, 1 992) . It is synthesized in the type II cells, and its
content in amnionic fluid increases with gestational age and
fetal lung maturity. SP-A gene expression is demonstrable by
29 weeks (Mendelson, 2005) . Specifically, SP-Ai and SP-A2
20
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Gestational age (weeks)
F I G U R E 7-1 2 Relatio n s h i p between the leve l s of l ecit h i n­
d i pa l mitoyl phosphatidylcholine (PC), phosphatidyl i n ositol (PI), and
phosphatidylg lycerol (PG) i n a m n ionic fl uid.
are two separate genes on chromosome 1 0, but their regulation
is distinctive and diferent (McCormick, 1 994) .
Several smaller apoproteins such as SP-B and SP-C are
likely important in optimizing the action of surfactant. For
example, deletions. in SP-B gene are incompatible with survival
despite production of large amounts of surfactant (Hallman,
20 1 3) .
Corticosteroids and Feta l Lung Matu ration. Since Liggins
( 1 969) observed accelerated lung maturation in lamb fetuses
given glucocorticosteroids prior to preterm delivery, many
suggested that fetal cortisol stimulates lung maturation and
surfactant synthesis. It is unlikely that corticosteroids are the
only stimulus for augmented surfactant formation. However,
when these are administered at certain critical times, they may
improve preterm fetal lung maturation. As fetal lung therapy,
antenatal betamethasone and dexamethasone use and neonatal
replacement surfactant therapy are discussed in Chapter 34
(p. 637) .
Breath i ng
Fetal respiratory muscles develop early, and chest wall move­
ments are detected sonographically as early as 1 1 weeks (Koos,
20 1 4) . From the beginning of the fourth month, the fetus
engages in respiratory movement suiciently intense to move
amnionic luid in and out of the respiratory tract. Some extra­
uterine events have efects on fetal breathing, for example,
maternal exercise stimulates it (Sussman, 20 1 6) .
• Digestive System
After its embryogenic formation from the yolk sac as the pri­
mordial gut, the digestive system forms the intestines and vari­
ous appendages. The foregut gives rise to the pharynx, lower
respiratory system, esophagus, stomach, proximal duodenum,
liver, pancreas, and biliary tree. The midgut gives rise to the
distal duodenum, jejunum, ileum, cecum, appendix, and the
right colon. The hindgut develops into the left colon, rectum,
and the superior portion of the anal canal. Numerous malfor­
mations develop in these structures from improper rotation,
ixation, and partitioning.
Swallowing begins at 1 0 to 1 2 weeks, coincident with the
ability of the small intestine to undergo peristalsis and actively
transport glucose (Koldovsky, 1 965). As a correlate, neo­
nates born preterm may have swallowing diiculties because
of immature gut motility (Singendonk, 20 1 4) . Much of the
water in swallowed luid is absorbed, and unabsorbed matter
is propelled to the lower colon. Gitlin ( 1 974) demonstrated
that late in pregnancy, approximately 800 mg of soluble pro­
tein is ingested daily by the fetus. he stimulus for swallow­
ing is unclear, but the fetal neural analogue of thirst, gastric
emptying, and change in the amnionic fluid composition are
potential factors (Boyle, 1 992) . The fetal taste buds may play
a role because saccharin injected into amnionic fluid increases
swallowing, whereas injection of a noxious chemical inhibits it
(Liley, 1 972) .
Fetal swallowing appears to have little efect on amnionic
fluid volume early in pregnancy because the volume swallowed
is small compared with the total. However, term fetuses swallow
E m b ryogenesis a nd Feta l Developm ent
between 200 and 760 mL per day-an amount comparable
to that of the term neonate (Pritchard, 1 966) . hus at term,
amnionic fl u id volume regulation can be substantially altered
by fetal swallowing. For example, as discussed in Chapter 1 1
(p. 227) , if swallowing is inhibited, hydramnios is common.
Hydrochloric acid and some digestive enzymes are pres­
ent in the stomach and small intestine in minimal amounts
in the early fetus. Intrinsic factor is detectable by 1 1 weeks,
and pepsinogen by 1 6 weeks. The preterm neonate, depending
on its gestational age, may have transient defi c iencies of these
enzymes (Lebenthal, 1 983) .
Stomach emptying appears to be stimulated primarily by
volume. Movement of amnionic luid through the gastroin­
testinal system may enhance growth and development of the
alimentary canal. That said, other regulatory factors likely are
involved. For example, anencephalic fetuses, in which swallow­
ing is limited, often have normal amnionic fluid volume and
normal-appearing gastrointestinal tract.
Mecon i u m
Fetal bowel contents consist o f various products o f secretion,
such as glycerophospholipids from the lung, desquamated fetal
cells, lanugo, scalp hair, and vernix. It also contains undigested
debris from swallowed amnionic fluid. The dark greenish-black
color forms from bile pigments, especially biliverdin. Meconium
can pass from normal bowel peristalsis in the mature fetus or
from vagal stimulation. It can also pass when hypoxia stimulates
arginine vasopressin (AVP) release from the fetal pituitary gland.
AVP stimulates colonic smooth muscle to contract, resulting in
intraamnionic defecation (deVane, 1 982; Rosenfeld, 1 985).
Meconium is toxic to the respiratory system, and its inhalation
can result in meconium aspiration syndrome (Chap. 33, p. 620) .
Liver
The hepatic diverticulum is an outgrowth of the endodermal
lining of the foregut. Epithelial liver cords and primordial cells
diferentiate into hepatic parenchyma. Serum liver enzyme
levels increase with gestational age. Still, the fetal liver has a
gestational-age-related diminished capacity for converting free
unconjugated bilirubin to conjugated bilirubin (Morioka,
2 0 1 5). Because of hepatic immaturity, the preterm new­
born is at particular risk for hyperbilirubinemia (Chap. 33,
p. 626) . And because the life span of normal fetal macrocytic
erythrocytes is shorter than that of the adult, relatively more
unconjugated bilirubin is produced. As j ust noted, the fetal
liver conjugates only a small fraction, and this is excreted into
the intestine and ultimately oxidized to biliverdin. Most of
the unconj ugated bilirubin is excreted into the amnionic luid
after 12 weeks and transferred across the placenta (Bashore,
1 969) .
Importantly, placental bilirubin transfer is bidirectional.
Thus, a woman with severe hemolysis from any cause has
excess unconjugated bilirubin that readily passes to the fetus
and then into the amnionic fluid. Conversely, conjugated
bilirubin is not exchanged to any signifi c ant degree between
mother and fetus.
Most fetal cholesterol derives from hepatic synthesis, which
satisies the large demand for low-density lipoprotein (LDL)
cholesterol by the fetal adrenal glands. Hepatic glycogen is pres­
ent in low concentration during the second trimester, but near
term, levels rise rapidly and markedly to reach concentrations
that are two- to threefold higher than those in the adult liver.
After birth, glycogen content falls precipitously.
Pa n crea s
This organ arises from dorsal and ventral pancreatic buds
from the endoderm of the foregut. Gene regulation of its
development was recently reviewed Qennings, 20 1 5) . Insu­
lin-containing granules can be identiied by 9 to 10 weeks,
and insulin is detectable in fetal plasma at 12 weeks (Adam,
1 969) . The pancreas responds to hyperglycemia by secreting
insulin (Obenshain, 1 970) . Glucagon has been identified in
the fetal pancreas at 8 weeks. Although hypoglycemia does
not cause an increase in fetal glucagon levels, similar stimuli
do so by 12 hours after birth (Chez, 1 975) . At the same time,
however, fetal pancreatic a cells do respond to L-dopa infu­
sions (Epstein, 1 977) . Therefore, unresponsiveness to hypo­
glycemia is likely the consequence of failed glucagon release
rather than inadequate production. This is consistent with
developmental expression of pancreatic genes in the fetus
(Mally, 1 994) .
Most pancreatic enzymes are present by 1 6 weeks. T ryp­
sin, chymotrypsin, phospholipase A, and lipase are found in
the 1 4-week fetus, and their concentrations increase with ges­
tational age (Wedin, 1 992) . Amylase has been identiied in
amnionic luid at 1 4 weeks (Davis, 1 986) . The exocrine func­
tion of the fetal pancreas is limited. Physiologically important
secretion occurs only after stimulation by a secretagogue such
as acetylcholine, which is released locally after vagal stimula­
tion (Werlin, 1 992). Cholecystokinin normally is released only
after protein ingestion and thus ordinarily would not be found
in the fetus.
• Urinary System
Renal development involves interaction between pluripotential
stem cells, undiferentiated mesenchymal cells, and epithelial
components (Fanos, 20 1 5) . Two primitive urinary systems­
the pronephros and the mesonephros-precede development
of the metanephros, which forms the inal kidney (Chap. 3,
p. 33) . The pronephros involutes by 2 weeks, and the meso­
nephros produces urine at 5 weeks and degenerates by 1 1 to
1 2 weeks. Failure of these two structures either to form or to
regress may result in anomalous urinary system development.
Between 9 and 12 weeks, the ureteric bud and the nephrogenic
blastema interact to produce the metanephros. he kidney and
ureter develop from intermediate mesoderm. The bladder and
urethra develop from the urogenital sinus. The bladder also
develops in part from the allantois.
By week 1 4, the loop of Henle is functional and reabsorp­
tion occurs (Smith, 1 992) . New nephrons continue to be
formed until 36 weeks. In preterm neonates, their formation
continues after birth. Although the fetal kidneys produce urine,
their ability to concentrate and modiy the pH is limited even
in the mature fetus. Fetal urine is hypotonic with respect to
fetal plasma and has low electrolyte concentrations.
1 35
1 36
Place ntati on, Em b ryogenesis, and Feta l Development
Renal vascular resistance is high, and the filtration fraction
is low compared with adult values (Smith, 1 992) . Fetal renal
blood low and thus urine pro d uction are controlled or inlu­
enced by the renin-angiotensin system, the sympathetic ner­
vous system, prostaglandins, kallikrein, and atrial natriuretic
peptide. The glomerular fi l tration rate increases with gesta­
tional age from less than 0. 1 mLimin at 1 2 weeks to 0.3 mLi
min at 20 weeks. In later gestation, the rate remains constant
when corrected for fetal weight (Smith, 1 992) . Hemorrhage
or hypoxia generally results in a decrease in renal blood flow,
glomerular filtration rate, and urine output.
Urine usually is found in the bladder even in small fetuses.
The fetal kidneys start producing urine at 1 2 weeks. By 1 8 weeks,
they are producing 7 to 14 mLi day, and at term, this increases
to 650 mLiday (Wladimirof, 1 974) . Maternally administered
furosemide increases fetal urine formation, whereas uteropla­
cental insuiciency, fetal growth restriction, and other fetal
disorders can lower it. Obstruction of the urethra, bladder,
ureters, or renal pelves can damage renal parenchyma and dis­
tort fetal anatomy (Muller Brochut, 2 0 1 4) . Kidneys are not
essential for survival in utero but inluence control of amnionic
luid composition and volume. hus, abnormalities that cause
chronic fetal anuria are usually accompanied by oligohydram­
nios and pulmonary hypoplasia. Pathological correlates and
prenatal therapy of urinary tract obstruction are discussed in
Chapter 1 6 (p. 325).
• Endocrine Gland Development
Pitu ita ry G l a nd
The fetal endocrine system is functional for some time before
the central nervous system reaches maturity (Mulchahey, 1 987) .
he anterior pituitary gland develops from oral ectoderm­
Rathke pouch, whereas the posterior pituitary gland derives
from neuroectoderm. As with other organ systems, embryonic
development involves a complex and highly spatiotemporally
regulated network of signaling molecules and transcription fac­
tors (Bancalari, 20 1 2; de Moraes, 20 1 2) .
Anterior a n d Intermediate Lobes. The adenohypophysis, or
anterior pituitary, diferentiates into five cell types that secrete
six protein hormones. Of these types, lactotropes produce pro­
lactin (PRL) , somatotropes produce growth hormone (GH),
corticotropes produce adrenocorticotropic hormone (ACTH) ,
thyrotropes produce thyroid-stimulating hormone (TSH), and
gonadotropes produce luteinizing hormone (LH) and follicle­
stimulating hormone (FSH).
ACTH is irst detected in the fetal pituitary gland at
7 weeks, and GH and LH have been identifi e d by 1 3 weeks.
By the end of the 1 7th week, the fetal pituitary gland synthe­
sizes and stores all pituitary hormones. Moreover, the fetal
pituitary is responsive to tropic hormones and is capable of
secreting these early in gestation (Grumbach, 1 974) . he
fetal pituitary secretes �-endorphin, and cord blood levels of
�-endorphin and �-lipotrophin rise with fetal PC0 2 (Brown­
ing, 1 983) .
The intermediate lobe in the fetal pituitary gland is well
developed. The cells of this structure begin to disappear before
term and are absent from the adult pituitary. he principal secre­
tory products of the intermediate lobe cells are .-melanocyte­
stimulating hormone (.-MSH) and �-endorphin.
Neurohypop hysis. The posterior pituitary gland or neurohy­
pophysis is well developed by 1 0 to 1 2 weeks, and oxytocin and
arginine vasopressin are demonstrable. Both hormones probably
unction in the fetus to conserve water by actions directed largely
at the lung and placenta rather than kidney. Vasopressin levels
in umbilical cord plasma are increased strikingly compared with
maternal levels (Chard, 1 97 1 ) .
Thyroid G l a n d
This gland arises from the endoderm o f the second pharyn­
geal pouch. he thyroid migrates to its inal position and the
obliterated thyroglossal duct connects to the foramen cecum of
the tongue. he pituitary-thyroid system is functional by the
end of the first trimester. The thyroid gland is able to synthe­
size hormones by 1 0 to 1 2 weeks, and thyrotropin, thyroxine,
and thyroid-binding globulin (TBG) have been detected in
fetal serum as early as 1 1 weeks (Bernal, 2007) . he placenta
actively concentrates iodide on the fetal side, and by 1 2 weeks
and throughout pregnancy, the fetal thyroid concentrates
iodide more avidly than does the maternal thyroid. hus,
maternal administration of either radioiodide or appreciable
amounts of ordinary iodide is hazardous after this time (Chap.
58, p. 1 1 2 1 ) . Normal fetal levels of free thyroxine (T4) , free
triiodothyronine (T3)' and thyroxin-binding globulin increase
steadily throughout gestation (Ballabio, 1 989). Compared
with adult levels, by 36 weeks, fetal serum concentrations of
TSH are higher, total and free T3 concentrations are lower,
and T4 is similar. This suggests that the fetal pituitary may
not become sensitive to feedback until late pregnancy (horpe­
Beeston, 1 99 1 ) .
Fetal thyroid hormone plays a role in the normal develop­
ment of virtually all fetal tissues, especially the brain (Forhead,
20 1 4 ; Rovet, 20 1 4) . Its inluence is illustrated by congenital
hyperthyroidism, which develops when maternal thyroid­
stimulating antibody crosses the placenta to stimulate the fetal
gland to secrete thyroxine (Donnelley, 20 1 5) . These fetuses
develop large goiters as shown in Figure 58-3 (p. 1 1 2 1 ) . They
also display tachycardia, hepatosplenomegaly, hematological
abnormalities, craniosynostosis, and growth restriction. As chil­
dren, they have perceptual motor diiculties, hyperactivity, and
reduced growth (Wenstrom, 1 990) . Fetal thyroid disease and
its treatment are discussed in Chapter 1 6 (p. 3 1 8) . Neonatal
efects of fetal thyroid deficiency are discussed in Chapter 58
(p. 1 1 26) .
The placenta prevents substantial passage of maternal thy­
roid hormones to the fetus by rapidly deiodinating maternal T4
and T3 to form reverse T 3' a relatively inactive thyroid hormone
(Vulsma, 1 989) . Several antithyroid antibodies cross the pla­
centa when present in high concentrations (Pelag, 2002) . Those
include the long-acting thyroid stimulators (LATS) , LATS­
protector (LATS-P) , and thyroid-stimulating immunoglobulin
(TSI) . It was previously believed that normal fetal growth and
development, which occurred despite fetal hypothyroidism,
provided evidence that T4 was not essential for fetal growth. It
E m b ryog enesis a n d Feta l Deve l opment
is now known, however, that growth proceeds normally because
small quantities of maternal T4 prevent antenatal cretinism in
fetuses with thyroid agenesis (Forhead, 20 1 4; Vulsma, 1 989).
The fetus with congenital hypothyroidism typically does not
develop stigmata of cretinism until after birth (Abduljabbar,
20 1 2) . Because administration of thyroid hormone will prevent
this, by state law, all newborns are tested for high serum levels
of TSH (Chap. 32, p. 6 1 4) .
Immediately after birth, thyroid function and metabolism
undergo major change. Cooling to room temperature evokes
sudden and marked increase in TSH secretion. his in turn
causes a progressive increase in serum T4 levels that are maximal
24 to 36 hours after birth. here are nearly simultaneous eleva­
tions of serum T3 levels.
Ad re n a l G l a n d s
These glands develop from two separate tissues. The medulla
derives from neural crest ectoderm, whereas the fetal and adult
cortex arise from intermediate mesoderm. The gland grows rap­
idly through cell proliferation and angiogenesis, cellular migra­
tion, hypertrophy, and apoptosis (Ishimoto, 20 1 1 ) . Fetal glands
are much larger in relation to total body size than in adults. he
bulk is made up of the inner or fetal zone of the adrenal cortex
and involutes rapidly after birth. his zone is scant to absent in
rare instances in which the fetal pituitary gland is congenitally
absent. he function of the fetal adrenal glands is discussed in
detail in Chapter 5 (p. 1 04) .
• Immunological System
Infections in utero have provided an opportunity to examine
mechanisms of the fetal immune response. Evidence of immu­
nological competence has been reported as early as 1 3 weeks
(Kohler, 1 973; Stabile, 1 988) . In cord blood at or near term,
the average level for most components is approximately half
that of the adult values (Adinolfi, 1 977) .
B cells diferentiate from pluripotent hemopoietic stem
cells that migrate to the liver (Melchers, 20 1 5 ; Muzzio, 20 1 3) .
Despite this, i n the absence o f a direct antigenic stimulus such
as infection, fetal plasma immunoglobulins consist almost
totally of transferred maternal immunoglobulin G (IgG) .
hus, antibodies in the newborn are most often relective
of maternal immunological experiences (American College
of Obstetricians and Gynecologists, 20 1 7) . he interaction
between maternal and fetal T cells is described in detail in
Chapter 5 (p. 95).
I m m u n og lo b u l i n G
Maternal IgG transport to the fetus begins at approximately
1 6 weeks and increases thereafter. he bulk of IgG is acquired
during the last 4 weeks of pregnancy (Gitlin, 1 97 1 ) . Accord­
ingly, preterm neonates are poorly endowed with protective
maternal antibodies. Newborns begin to slowly produce IgG,
and adult values are not attained until age 3 years. In certain
situations, the transfer of IgG antibodies from mother to fetus
can be harmful rather than protective to the fetus. The classic
example is hemolytic disease of the fetus and newborn resulting
from Rh-antigen alloimmunization (Chap. 1 5 , p. 30 1 ) .
I m m u n og lo b u l i n s M a nd A
In the adult, production of immunoglobulin M (IgM) in
response to an antigenic stimulus is superseded in a week or
so predominantly by IgG production. In contrast, very little
IgM is produced by normal fetuses. With infection, the IgM
response is dominant in the fetus and remains so for weeks
to months in the newborn. And, because IgM is not trans­
ported from the mother, any IgM in the fetus or newborn is
that which it produced. hus, specific IgM levels in umbilical
cord blood may be useful in fetal infection diagnosis. Accord­
ing to the American College of Obstetricians and Gynecologists
(20 1 7) , elevated levels of IgM are usually found in newborns
with congenital infection such as rubella, cytomegalovirus
infection, or toxoplasmosis. In infants, adult levels of IgM are
normally attained by age 9 months.
Immunoglobulin A (IgA) ingested in colostrum provides
mucosal protection against enteric infections. This may explain
the small amount of fetal secretory IgA found in amnionic luid
(Quan, 1 999) .
Lym p h ocytes a n d Monocytes
he immune system develops early, and B lymphocytes appear
in fetal liver by 9 weeks and in blood and spleen by 1 2 weeks.
T lymphocytes begin to leave the thymus at approximately 1 4
weeks. Despite this, the newborn responds poorly t o immuniza­
tion, and especially poorly to bacterial capsular polysaccharides.
his immature response may stem from a deicient response of
newborn B cells to polyclonal activators or from a lack of T
cells that proliferate in response to specific stimuli (Hayward,
1 983). In the newborn, monocytes are able to process and pres­
ent antigen when tested with maternal antigen-speciic T cells.
DNA methylation patterns are developmentally regulated dur­
ing monocyte-macrophage diferentiation and contribute to
the antiinlammatory phenotype in macro phages (Kim, 2 0 1 2) .
• Musculoskeletal System
The origin of most muscles and bones is mesodermal. he skel­
eton arises from condensed mesenchyme-embryonic connec­
tive tissue-which eventually forms hyaline cartilage models of
the bones. By the end of the embryonic period, ossifi c ation cen­
ters have developed, and bones harden by endochondral ossifi­
cation. The limb buds appear by the fourth week. Most skeletal
muscle derives from myogenic precursor cells in the somites.
EN ERGY AND NUTRITION
Because of the small amount of yolk in the human ovum, growth
of the embryofetus is dependent on maternal nutrients during
the irst 2 months. During the fi r st few days after implantation,
blastocyst nutrition comes from the interstitial fl u id of the endo­
metrium and the surrounding maternal tissue.
Maternal adaptations to store and transfer nutrients to
the fetus are discussed in Chapter 4 and summarized here. Three
major maternal storage depots are the liver, muscle, and adipose
tissue. These maternal depots and the storage hormone insu­
lin are intimately involved in the metabolism of the nutrients
absorbed from the gut. Maternal insulin secretion is sustained
1 37
1 38
Pl ace ntation, E m b ryogenes is, a n d Feta l Deve l o p m ent
by increased serum levels of glucose and amino acids. he net
efect is maternal storage of glucose as glycogen primarily in
liver and muscle, retention of some amino acids as protein, and
storage of the excess as fat. Storage of maternal fat peaks in the
second trimester and then declines as fetal energy demands rise
in the third trimester (Pipe, 1 979) . Interestingly, the placenta
appears to act as a nutrient sensor, altering transport based on
the maternal supply and environmental stimuli (Fowden, 2006;
Jansson, 2006b) .
During times of fasting, glucose is released from glyco­
gen, but maternal glycogen stores cannot provide an adequate
amount of glucose to meet requirements for maternal energy
and fetal growth. Augmentation is provided by cleavage of tria­
cylglycerols, stored in adipose tissue, which result in free fatty
acids and activation of lipolysis.
• Glucose and Fetal Growth
Although dependent on the mother for nutrition, the fetus also
actively participates in providing its own nutrition. At mid­
pregnancy, fetal glucose concentration is independent of mater­
nal levels and may exceed them (Bozzetti, 1 988). Glucose is the
major nutrient for fetal growth and energy. Logically, mecha­
nisms exist during pregnancy to minimize maternal glucose use
so that the limited maternal supply is available to the fetus.
Human placental lactogen (hPL), a hormone normally abun­
dant in the mother bur not the fetus, has an insulin antagonist
efect. It blocks the peripheral uptake and use of glucose, while
promoting mobilization and use of free fatty acids by maternal
tissues (Chap. 5, p. 1 00) . his hormone is also diabetogenic as
discussed in Chapter 57 (p. 1 1 07) .
G l u cose Tra nsport
he transfer of D-glucose across cell membranes is accomplished
by a carrier-mediated, stereospecific, nonconcentrating process
of facilitated difusion. There are 14 glucose transport proteins
(GLUTs) encoded by the SLC2A gene family and characterized
by tissue-speciic distribution (Leonce, 2006) . GLUT- 1 and
GLUT-3 primarily facilitate glucose uptake by the placenta and
are located in the plasma membrane of the syncytiotrophoblast
microvilli (Acosta, 20 1 5) . DNA methylation regulates expres­
sion of placental GL UT genes, with epigenetic modiication
across gestation (Novakovic, 20 1 3) . It increases as pregnancy
advances and is induced by almost all growth factors (Frolova,
20 1 1 ) . GLUT-3 expression is upregulated with fetal growth
restriction a anzen, 20 1 3) .
Lactate i s a product o f glucose metabolism and transported
across the placenta also by facilitated difusion. By way of
cotransport with hydrogen ions, lactate is probably transported
as lactic acid.
Feta l Macrosom i a
The precise biomolecular events in the pathophysiology of
fetal macrosomia are not deined. Nonetheless, fetal hyperin­
sulinemia is clearly one driving force (Luo, 20 1 2) . As discussed
in Chapter 44 (p. 845), insulin-like growth factor, fibroblast
growth factor, and corticotropin-releasing hormone (CRH)
and are important regulators of placental development and
function (Gao, 20 1 2 ; Giudice, 1 995). Maternal obesity begets
fetal macrosomia (Chap. 44, p. 857). In addition, it is hypoth­
esized that maternal obesity afects fetal cardiomyocyte growth
that may result in fetal cardiomyopathy or even congenital
heart disease (Roberts, 20 1 5) .
• Leptin
This polypeptide hormone was originally identified as a prod­
uct of adipocytes and a regulator of energy homeostasis by
curbing appetite. It also contributes to angiogenesis, hemopoi­
esis, osteogenesis, pulmonary maturation, and neuroendocrine,
immune, and reproductive functions (Brifa, 20 1 5 ; Maymo,
2009). Leptin is produced by the mother, fetus, and placenta.
It is expressed in syncytiotrophoblast and fetal vascular endo­
thelial cells. Of placental production, 5 percent enters the fetal
circulation, whereas 95 percent is transferred to the mother
(Hauguel-de vlouzon, 2006) . Leptin concentrations peak in
amnionic fluid at midpregnancy (Scott-Finley, 20 1 5) .
Fetal leptin levels begin rising a t approximately 3 4 weeks and
are correlated with fetal weight. This hormone is involved in the
development and maturation of the heart, brain, kidneys, and
pancreas, and its levels are decreased with fetal growth restric­
tion (Brifa, 20 1 5) . Abnormal levels have been associated with
fetal growth disorders, gestational diabetes, and preeclampsia
(Fasshauer, 20 1 4) . Postpartum, leptin levels decline in both the
newborn and mother. Perinatal leptin is associated with the
development of metabolic syndromes later in life (Brifa, 20 1 5 ;
Granado, 20 1 2) .
• Free Fatty Acids a n d Triglycerides
The newborn has a large proportion of fat, which averages 1 5
percent of body weight (Kimura, 1 99 1 ) . Thus, late in pregnancy,
a substantial part of the substrate transferred to the human fetus
is stored as fat. Although maternal obesity raises placental fatty
acid uptake and fetal fat deposition, it does not appear to afect
fetal organ growth (Dube, 20 1 2) . Neutral fat in the form of tri­
glycerides does not cross the placenta, but glycerol does. Despite
this, evidence supports that abnormal maternal concentrations
of triglycerides-both low and high levels-are associated with
major congenital anomalies (Nederlof, 20 1 5) .
There i s preferential placental-fetal transfer o f long-chain
polyunsaturated fatty acids (Gil-Sanchez, 20 1 2) . Lipoprotein
lipase is present on the maternal but not on the fetal side of the
placenta. his arrangement favors hydrolysis of triacylglycerols
in the maternal intervillous space yet preserves these neutral
lipids in fetal blood. Fatty acids transferred to the fetus can be
converted to triglycerides in the fetal liver.
The placental uptake and use of LDL is an alternative mech­
anism for fetal assimilation of essential fatty acids and amino
acids (Chap. 5, p. 1 03). LDL binds to specific receptors in the
coated-pit regions of the syncytiotrophoblast microvilli. The
large LDL particle, measuring about 250,000 Da, is taken up
by a process of receptor-mediated endocytosis. The apopro­
tein and cholesterol esters of LD L are hydrolyzed by lysosomal
enzymes in the syncytium to yield: ( 1 ) cholesterol for proges­
terone synthesis; (2) free amino acids, including essential amino
acids; and (3) essential fatty acids, primarily linoleic acid.
E m b ryogenesis a n d Feta l Develop ment
• Amino Acids
he placenta concentrates many amino acids in the syncytiotro­
phoblast, which are then transferred to the fetal side by difusion.
Based on data from cordocentesis blood samples, the amino acid
concentration in umbilical cord plasma is greater than in mater­
nal venous or arterial plasma (Morriss, 1 994) . Transport system
activity is influenced by gestational age and environmental fac­
tors. hese include heat stress, hypoxia, under- and overnutri­
tion, and hormones such as glucocorticoids, growth hormone,
and leptin (Brifa, 20 1 5; Fowden, 2006) . Trophoblastic mam­
malian target of rapamycin complex 1 (mTORC 1 ) regulates
placental amino acid transporters and modulates transfer across
the placenta Qansson, 20 1 2) . In vivo studies suggest an upregu­
lation of transport for certain amino acids and a greater delivery
rate of these to the fetuses of women with gestational diabetes
associated with fetal overgrowth Oansson, 2006a) .
• Proteins
Placental transfer of larger proteins is limited, but there are
exceptions. IgG crosses the placenta in large amounts via endo­
cytosis and trophoblast Fc receptors. IgG transfer depends on
maternal levels of total IgG, gestational age, placental integrity,
IgG subclass, and antigenic potential (Palmeira, 20 1 2) . Con­
versely, the larger immunoglobulins-IgA and IgM-of mater­
nal origin are efectively excluded from the fetus.
• Ions and Trace Metals
Calcium and phosphorus are actively transported from mother
to fetus. Calcium is transferred for fetal skeletal mineralization
(Olausson, 20 1 2) . A calcium-binding protein is produced in
placenta. Parathyroid hormone-related protein (PTH-rP) , as
the name implies, acts as a surrogate PTH in many systems
(Chap. 5, p. 1 02) . PTH is not found in fetal plasma, but PTH­
rP is present, suggesting that PTH-rP is the fetal parathormone.
The expression of PTH-rP in cytotrophoblasts is modulated
by the extracellular concentration of Ca2 + (Hellman, 1 992) . It
seems possible, therefore, that PTH-rP synthesized in decidua,
placenta, and other fetal tissues is important in fetal Ca2 + trans­
fer and homeostasis.
Iodide transport is clearly attributable to a carrier-mediated,
energy-requiring active process. And indeed, the placenta con­
centrates iodide. he concentrations of zinc in the fetal plasma
also are greater than those in maternal plasma. Conversely, cop­
per levels in fetal plasma are less than those in maternal plasma.
his fact is of particular interest because important copper­
requiring enzymes are necessary for fetal development.
Placenta l Seq uestration of H eavy Meta l s
h e heavy metal-binding protein metallothionein- 1 i s expressed
in human syncytiotrophoblast. his protein binds and seques­
ters a host of heavy metals, including zinc, copper, lead, and
cadmium. Despite this, fetal exposure is variable (Caserta,
20 1 3) . For example, lead enters the fetal environment at a level
90 percent of maternal concentrations. In contrast, placental
transfer of cadmium is limited (Kopp, 20 1 2) . he most com­
mon source of environmental cadmium is cigarette smoke.
Metallothionein also binds and sequesters copper (Cu2 +) in
placental tissue. This accounts for the low levels of Cu2+ in cord
blood (Iyengar, 200 1 ) . It is possible that cadmium provokes
metallothionein synthesis in the amnion. his may cause Cu2 +
sequestration, a pseudo-copper deficiency, and in turn, dimin­
ished tensile strength of the amnion.
• Vitamins
he concentration of vitamin A (retinol) is greater in fetal than
in maternal plasma and is bound to retinol-binding protein
and to prealbumin. Retinol-binding protein is transferred from
the maternal compartment across the syncytiotrophoblast. The
transport of vitamin C-ascorbic acid-from mother to fetus
is accomplished by an energy-dependent, carrier-mediated
process. Levels of principal vitamin D metabolites, including
1 ,25-dihydroxycholecalciferol, are greater in maternal plasma
than in fetal plasma. The 1 3-hydroxylation of 25-hydroxyvi­
tamin D3 is known to take place in placenta and in decidua.
PLACENTAL ROLE IN EM BRYOFETAL
DEVELOPMENT
The placenta is the organ of transfer between mother and fetus.
Within this maternal-fetal interface, oxygen and nutrients
transfer from the mother to the fetus, whereas CO 2 and meta­
bolic wastes are directed from fetus to mother. Fetal blood,
which is contained in the fetal capillaries of the chorionic villi,
has no direct contact with maternal blood, which remains in
the intervillous space. Instead, bidirectional transfer depends
on processes that allow or aid the transport through the syncy­
tiotrophoblast that lines chorionic villi.
Over the past few years, it has become apparent that breaks
in the chorionic villi permit escape of fetal cells and other blood­
borne material into the maternal circulation. This leakage is the
mechanism by which some D-negative women become sensi­
tized by the erythrocytes of their D-positive fetus (Chap. 1 5,
p. 30 1 ) . In fact, after 1 0 weeks, 1 0 to 1 5 percent of cell-free
DNA (cDNA) in maternal plasma is placental in origin, that
is, trophoblastic DNA (Norton, 20 1 2) . he escape of fetal cells
can also lead to fetal microchimerism from entrance of alloge­
neic fetal cells, including trophoblast, into maternal blood and
other organs (Rijnik, 20 1 5) . Volumes are estimated to range
from 1 to 6 cells/ mL at midpregnancy. Some fetal cells become
"immortal" in that they persist in the maternal circulation
and organs following pregnancy. As discussed in Chapter 59
(p. 1 1 39) , the clinical corollary is that some maternal autoim­
mune diseases may be provoked by such microchimerism.
• The I ntervillous Space
v Iaternal blood within the intervillous space is the primary
source of maternal-fetal transfer. Blood from the maternal spiral
arteries directly bathes the trophoblast layer that surrounds the
villi. Substances transferred from mother to fetus irst enter the
intervillous space and are then transported to the syncytiotro­
phoblast. As such, the chorionic villi and intervillous space func­
tion together as the fetal lung, gastrointestinal tract, and kidney.
1 39
1 40
P l acentation, E m b ryoge n es i s, a n d Feta l Deve l opment
Circulation within the intervillous space is described in
Chapter 5 (p. 94) . Intervillous and uteroplacental blood flow
increases throughout the irst trimester of normal pregnancies
(Merce, 2009) . At term, the residual volume of the intervillous
space approximates 1 40 mL. Moreover, utero placental blood
flow near term is estimated to be 700 to 900 mLl min, and most
of this blood apparently goes to the intervillous space (Pates,
20 1 0) .
Active labor contractions reduce blood low into the inter­
villous space to a degree that depends on contraction intensity.
Blood pressure within the intervillous space is signifi c antly less
than uterine arterial pressure, but somewhat greater than venous
pressure. he latter, in turn, varies depending on several factors,
including maternal position (Nelson, 20 1 5) . When supine, for
example, pressure in the lower part of the inferior vena cava is
elevated, and consequently, pressure in the uterine and ovarian
veins, and in turn in the intervillous space, is increased.
• Placental Transfer
Substances that pass from maternal to fetal blood must irst
traverse the syncytiotrophoblast, the attenuated cytotropho­
blast layer, the villous stroma, and inally, the fetal capillary
wall. Although this histological barrier separates maternal
and fetal circulations, it is not a simple physical barrier. First,
throughout pregnancy, syncytiotrophoblast actively or pas­
sively permits, facilitates, and adjusts the amount and rate of
substance transfer to the fetus. The maternal-facing syncytio­
trophoblast surface is characterized by a complex microvillous
structure. he fetal-facing basal cell membrane is the site of
transfer to the intravillous space. Finally, the villous capillaries
are an additional site for transport from the intravillous space
into fetal blood, or vice versa. In determining the efectiveness
of the human placenta as an organ of transfer, several variables
are important and shown in Table 7- 1 . Zhao and coworkers
(20 1 4) have provided a review of the pharmacology of these
interactions.
Mech a n i s m s of Tra n sfer
Most substances with a molecular mass < 500 Da pass read­
ily through placental tissue by simple difusion. These include
oxygen, CO 2 , water, most electrolytes, and anesthetic gases
(Carter, 2009) . Some low-molecular-weight compounds
undergo transfer facilitated by syncytiotrophoblast. These are
usually those that have low concentrations in maternal plasma
but are essential for normal fetal development.
Insulin, steroid hormones, and thyroid hormones cross
the placenta, but very slowly. he hormones synthesized in
situ in the syncytiotrophoblast enter both the maternal and
fetal circulations, but not equally (Chap. 5, p. 9 8 ) . Examples
are hCG and hPL concentrations, which are m uch lower
in fetal plasma than in maternal plasma. H igh-molecular­
weight substances usually do not traverse the placenta, but
there are important exceptions. One is immunoglobulin
G-molecular weight 1 60,000 Da-which is transferred by
way of a speciic trophoblast receptor-mediated mechanism
(Stach, 20 1 4) .
Tra n sfer o f Oxyge n a n d Carbon Diox i d e
Placental oxygen transfer is blood flow limited. Using esti­
mated uteroplacental blood low, Longo ( 1 99 1 ) calculated
oxygen delivery to be approximately 8 mL 02/min/kg of fetal
weight. Normal values for oxygen and CO 2 are presented in
Figure 7- 1 3. Because of the continuous passage of oxygen from
maternal blood in the intervillous space to the fetus, its oxygen
saturation resembles that in maternal capillaries. The average
oxygen saturation of intervillous blood is estimated to be 65 to
75 percent, with a partial pressure (P02) of 30 to 35 mm Hg.
70
60
; 50
E
10
58
1 mm Hg approx.
0. 1 33 kPa
1 8 20 22 24 26 28 30 32 34 36 38 40
=
=
Gestation (weeks)
;
:
E
E
Tra n sfer
n
--
O -��-
A
TABLE 7-1 . Va r i a b l es of Materna l-Feta l S u bsta nce
Matern a l plasma concentration a n d carrier-protei n
b i n d i n g of the s u bsta n ce
Maternal b lood flow rate t h ro u g h the i nterv i l l o u s space
Trophoblast s u rface a rea size ava i la ble for exc h a n g e
P hysical t rophoblast p roperties to perm it s i m p l e d ifu sion
Trophoblast bioch e m ical m a c h i n e ry for active tra n s po rt
Su bsta nce meta b o l i s m by the pl ace nta d u ri ng tra nsfer
Feta l i n te rvi l lo u s cap i l l a ry su rface a rea size for exc h a n g e
Feta l b lood concentrat i o n o f the su bsta nce
Specific b i n d i n g o r carrier p rote i ns in the feta l o r mate r n a l
ci r c u lation
Vi l lo u s ca p i l l a ry b l ood fl ow rate
40
.N 30
. 20
:
---
50
40
30
-;
20
o
J
..
B
10
1 8 20 22 24 26 28 30 32 34 36 38 40
Gestation (weeks)
F I G U R E 7-1 3 U m b i l ical venous cordocentesis sam ples obta i ned
in fetu ses bei n g eva l uated for possi ble i ntra uteri ne i nfections or
hemolysis, but who were fou n d to be hea lthy. A. Oxygen press u re
(PoJ B. Carbon d ioxide pressure (Pco 2). Shaded a reas represent
5th to 95th percentiles. (Mod ified from Ramsey, MM: Norm a l Va l ues
in Preg n a ncy. Ramsay MM, J a mes OK, Steer PJ, et al (eds). London,
El sevier, 1 996, p 1 06.)
E m b ryoge n esis a n d F eta l Develo pment
The oxygen saturation of umbilical vein blood is similar but
has a somewhat lower oxygen partial pressure. Fetal hemoglo­
bin has a higher oxygen ainity than adult hemoglobin. This is
illustrated by the oxyhemoglobin disassociation curve, which is
described in Chapter 47 (p. 920) .
he placenta is highly permeable to CO2, which traverses the
chorionic villus by diusion more rapidly than oxygen. Near
term, the partial pressure of carbon dioxide (PC02) in the umbili­
cal arteries averages 50 mm Hg, which is approximately 5 mm Hg
higher than in the maternal intervillous blood. Fetal blood has less
ainity for CO2 than does maternal blood, thereby favoring CO2
transfer from fetus to mother. Also, mild maternal hyperventila­
tion results in a fall in Pc02 levels, favoring a transfer of CO2 from
the fetal compartment to maternal blood.
Sel ective Tra nsfer a n d Faci l itated Diffusion
Although simple difusion is an important method of placental
transfer, the trophoblast and chorionic villus unit demonstrate
enormous selectivity in transfer. his results in diferent metab­
olite concentrations on the two sides of the villus. Importantly,
the levels of many substances that are not synthesized by the
fetus are several times higher in fetal than in maternal blood.
Ascorbic acid is one example. his relatively low-molecular­
weight substance might be expected to traverse the placenta by
simple difusion. he concentration of ascorbic acid, however,
is two to four times higher in fetal plasma than in maternal
plasma (Morriss, 1 994) . Another example is the unidirectional
transfer of iron. Typically, maternal plasma iron concentration
is much lower than that in her fetus. Even with severe maternal
iron-deficiency anemia, the fetal hemoglobin mass is normal.
REFERENCES
Abduljabbar MS, ii M: Congenital hypothyroidism. ] Pediatr Endocrinol
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P reco n ce pt i o n a l Ca re
COUNSELING SESSION . . . . . . . . . . . . . . . . . . . . . . . . . . 1 47
MEDICAL H I STORY. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 47
GENETIC DISEASES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 49
REPRODUCTIVE HISTORY . . . . . . . . . . . . . . . . . . . . . . . . 1 5 1
PARENTAL AGE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 5 1
SOCIAL HISTORY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 52
SCREEN I N G TESTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 53
Pregnancy may be associated with certain diseases that
existed bore the inception ofpregnancy. As a rule, all dis­
eases which subject the organism to a considerable strain are
much more serious when occurring in a pregnant woman.
-J. Whitridge Williams ( 1 903)
he Centers for Disease Control and Prevention (CDC) (20 1 5)
defines preconceptional care as "a set of interventions that aim
to identiy and modiy biomedical, behavioral, and social risks
to a woman's health or pregnancy outcome through preven­
tion and management." To achieve this goal, the CDC has
developed an action plan for preconceptional health care in
the United States Qohnson, 2006). The American College of
Obstetricians and Gynecologists (20 1 7 e) and the Society for
Maternal-Fetal 1vI edicine (20 1 4) also reairm the importance
of preconceptional care, and the following objectives have been
established for advancing it:
1 . Improve knowledge, attitudes, and behaviors of men and
women related to preconceptional health
2. Assure that all childbearing-aged women receive preconcep­
tional care services-including evidence-based risk screen­
ing, health promotion, and interventions-that will enable
them to enter pregnancy in optimal health
3. Reduce risks indicated by a previous adverse pregnancy out­
come through interconceptional interventions to prevent or
minimize recurrent adverse outcomes
4. Reduce the disparities in adverse pregnancy outcomes
To illustrate potentilly modifiable conditions, data that
describe the health status of women who delivered liveborn
neonates in the United States in 2004 are reviewed. Table 8- 1
demonstrates the high prevalence of many conditions that may
be amenable to intervention during the preconceptional and
interpregnancy periods. To be successul, however, strategies that
mitigate these potential pregnancy risks must be provided before
conception. By the time most women realize they are pregnant­
usually 1 to 2 weeks ater the first missed period-the embryo has
already begun to form. hus, many preventive steps-for exam­
ple, folic acid to avoid neural-tube defects-will be inefective if
initiated at this time. Importantly, up to half of all pregnancies
in the United States in 2008 were unplanned according to the
Guttmacher Institute (20 1 5) , and oten these are at greatest risk.
Few randomized trials evaluate preconceptional counseling
eicacy, in part because withholding such counseling would
be unethical. Also, pregnancy outcomes are dependent on the
interaction ofvarious maternal, fetal, and environmental factors.
hus, ascribing a salutary outcome to a specific intervention
is diicult (Moos, 2004; Temel, 20 1 4) . However, prospective
observational and case-control studies have demonstrated the
successes of preconceptional counseling (American College of
Obstetrics and Gynecologists, 20 1 6b) . \100s and coworkers
( 1 996) assessed the efectiveness of a preconceptional counseling
program administered during routine health care provision to
reduce unintended pregnancies. he 456 counseled women had
a 50-percent greater likelihood of subsequent pregnancies that
they considered "intended" compared with 309 uncounseled
P reconceptiona l C a re
TABLE 8- 1 . Preva lence of Prepregna ncy Materna l
Behaviors, Experiences, Hea lth Cond itions,
a n d Previous Poor B i rth Outcomesa
Factor
Tobacco use
Alcohol use
M u ltivita m i n u se
Contrace ptive non use b
Dental visit
Hea lth co u n se l i ng
P hysica l a buse
Stress
U n derwei g ht
Overweight
Obesity
Dia betes
Asthma
Hypertension
Hea rt problem
Anemia
Prior low-bi rthwe i g ht neonate
Prior preterm neonate
Prevalence (%)
23
50
35
53
78
30
4
19
13
l3
22
2
7
2
1
10
12
12
a l n the U n ited States i n 2004.
bAmong women who were n ot trying to become p reg n a nt.
Data from D'Angelo D, Wi l l ia m s L, Morrow 8, et al: P recon­
ception and i nterconception health status of women who
recently gave b i rth to a l ive-born i n fant-Preg nancy Risk
Assessment Monitori ng System (PRAMS), U n ited States, 2 6
reporting areas, 2004. M MWR 56(1 0): 1 , 2007.
women. Moreover, compared with another group of women
who had no health care before pregnancy, the counseled group
had a 65-percent higher rate of intended pregnancy. Interesting
ethical aspects of paternal lifestyle modification were reviewed
by van der Zee and associates (20 1 3) .
COUNSELING SESSION
Gynecologists, internists, family practitioners, and pediatricians
have the best opportunity to provide preventive counseling dur­
ing periodic health maintenance examinations. The occasion of
a negative pregnancy test is also an excellent time for education.
Jack and colleagues ( 1 995) administered a comprehensive precon­
ceptional risk survey to 1 36 such women, and almost 95 percent
reported at least one problem that could afect a uture preg­
nancy. These included medical or reproductive problems-52
percent; family history of genetic disease-50 percent; increased
risk of human immunodeiciency virus infection-30 percent;
increased risk of hepatitis B and illegal substance abuse-25 per­
cent; alcohol use- 1 7 percent; and nutritional risks-54 percent.
Counselors should be knowledgeable regarding relevant medical
diseases, prior surgery, reproductive disorders, or genetic condi­
tions and must be able to interpret data and recommendations
provided by other specialists (Simpson, 20 1 4) . If the practitio­
ner is uncomfortable providing guidance, the woman or couple
should be referred to an appropriate counselor.
Women presenting specifically for preconceptional evalua­
tion should be advised that information collection may be time
consuming, depending on the number and complexity of factors
that require assessment. he intake evaluation includes a thorough
review of the medical, obstetrical, social, and family histories. Use­
ul information is more likely to be obtained by asking specific
questions regarding each of these histories and each family mem­
ber than by asking general, open-ended questions. Some important
information can be obtained by questionnaires that address these
topics. Answers are reviewed with the couple to ensure appropriate
follow-up, including obtaining relevant medical records.
MEDICAL HISTORY
With specific medical conditions, general points include how preg­
nancy will afect maternl health and how a high-risk condition
might afect the fetus. terward, advice for improving outcome is
provided. Some chronic conditions that may ffect pregnancy out­
comes include treated or active cancer, prior peripartum cardiomy­
opathy, and systemic lupus erythematosus (mant, 20 1 5; Buyon,
20 1 5; McNamara, 20 1 5) . Importantly, psychological health should
be considered (Lassi, 20 1 4). Detailed preconceptional information
regarding a few exemplary conditions is found in the next sections
and in the other topic-speciic chapters of this text.
• Diabetes Mellitus
Because maternal and fetal pathology associated with hypergly­
cemia is well known, diabetes is the protoype of a condition
for which preconceptional counseling is benefi c ial. Diabetes­
associated risks to both mother and fetus are discussed in detail
in Chapter 57 (p. 1 099) . Many of these complications can
be avoided if glucose control is optimized before conception.
Another important aspect of counseling pertains to the frequent
use of teratogenic angiotensin-converting enzyme inhibitors in
this population (Podymow, 20 1 5) .
The American College o f Obstetricians and Gynecologists
(20 1 6a) has concluded that preconceptional counseling for
women with pregestational diabetes is both beneicial and cost­
efective and should be encouraged. The American Diabetes
Association has promulgated consensus recommendations for
preconceptional care for diabetic women (Kitzmiller, 2008) .
hese guidelines advise obtaining a thorough inventory of dis­
ease duration and related complications and completing a clinical
and laboratory examination for end-organ damage. Perhaps most
essential, they encourage a preconceptional goal of the lowest
hemoglobin Ale level possible without undue hypoglycemic risk
to the mother. In addition to assessing diabetic control during
the preceding 6 weeks, hemoglobin Ale measurement can also
be used to estimate risks for major anomalies as shown in Figure
8- 1 . lthough these data are from women with severe overt dia­
betes, the incidence of fetal anomalies in women who have ges­
tational diabetes with fasting hyperglycemia is increased fourfold
compared with that in normal women (Sheield, 2002) .
Such counseling in diabetic women has been shown to be
efective. Leguizam6n and associates (2007) identiied 1 2 studies
that included more than 3200 pregnancies in women with
insulin-dependent diabetes. Of the 1 6 1 8 women without precon-
1 47
1 48
P recon ce ptiona l a n d P renata l C a re
c
0
;
l
E
.. c
a _
o )
6 i
E�
-
0
'u
E
..
u
21
10
5
4.6-7.6
7.7-8.6
8 . 7-9.9
1 0 -1 0.5
Glycosylated hemoglobin (percent)
>
1 0.6
FIGURE 8-1 Relatio n s h i p between fi rst-tri m ester g lycosylated
hemog l o b i n val ues and risk for major con g e n ita l malformations i n
320 women with insulin-dependent d ia betes. (Data from Kitzm iller JL,
Gavin LA, G i n G O, et a l : Preconception care of d ia betics. JAMA
265:73 1 , 1 99 1 .)
ceptional counseling, 8.3 percent had a fetus with a major congeni­
tal anomaly, and this compared with a rate of 2.7 percent in the
1 599 women who did have counseling. Tripathi and coworkers
(20 1 0) compared outcomes in 588 women with pregestational
diabetes in whom approximately half had preconceptional coun­
seling. hose women who received counseling had improved gly­
cemic control before pregnancy and in the first trimester. his
group also had higher folate intake rates preconceptionally, and
they experienced lower rates of adverse outcomes-deined as a
perinatal death or major congenital anomaly. hese cited ben­
eits are accompanied by reduced helth-care costs in diabetic
women. From their review, Reece and Homko (2007) found
that each $ 1 expended for a preconceptional care program saved
between $ 1 .86 and $5. 1 9 in averted medical costs. Despite such
beneits, the proportion of diabetic women receiving preconcep­
tional care is suboptimal. In their study of approximately 300
diabetic women in a managed-care plan, Kim and colleagues
(2005) found that only approximately one half had preconcep­
tional counseling. Counseling rates are undoubtedly much lower
among uninsured and indigent women.
• Epilepsy
Compared with unafected women, those with a seizure disor­
der carry an undisputed augmented risk of having neonates with
structural anomalies (Chap. 1 2, p. 240) . Some early reports
indicated that epilepsy conferred an elevated a priori risk for
congenital malformations that was independent of anticon­
vulsant treatment efects. Although more recent publications
have largely failed to conirm this increased risk in untreated
women, it is diicult to refute entirely because women who are
controlled without medication generally have less severe disease
(Cassina, 20 1 3 ; Vajda, 20 1 5) . Fried and associates (2004) con­
ducted a metaanalysis of studies comparing epileptic women,
both treated and untreated, with controls. In this study, greater
malformation rates could only be demonstrated in the ofspring
of women who had been exposed to anticonvulsant therapy.
Veiby and coworkers (2009) used the Medical Birth Registry
of Norway and identiied an increased malformation risk only
in women who were exposed to valproic acid (5.6 percent) or
polytherapy (6. 1 percent) . Untreated women had anomaly
rates that were similar to those of nonepileptic controls. Risks
for miscarriage and stillbirths in exposed epileptic women do
not appear elevated (Aghajanian, 20 1 5 ; Bech, 20 1 4) .
Ideally, seizure control i s optimized preconceptionlly. For
example, Vajda and colleagues (2008) nalyzed data from the Aus­
tralian Register of Antiepileptic Drugs in Pregnancy. hey found
the seizure risk during pregnancy was 50- to 70-percent lower in
women without a seizure in the year preceding pregnancy com­
pared with a group experiencing seizures in this preceding year. No
urther advantages accrued if the seizure-free period exceeded a year.
Treatment goals attempt to achieve seizure control with
monotherapy and with medications considered less terato­
genic (Aguglia, 2009; Tomson, 2009) . As discussed in detail in
Chapter 60 (p. 1 1 59) and shown in Table 8-2, some one-drug
regimens are more teratogenic than others. Valproic acid, in par­
ticular, is avoided if possible, as this medication has consistently
been associated with a greater risk for major congenital malfor­
mations than other antiepileptic drugs Qentink, 20 1 0; Vajda,
20 1 5). Trimethadione is contraindicated (Aghajanian, 20 1 5) .
h e American Academy o f Neurology recommends consider­
ation of antiseizure medication discontinuation before pregnancy
in suitable candidates Qeha, 2005). hese include women who
satisy the following criteria: ( 1 ) have been seizure-free for 2 to
5 years, (2) display a single seizure type, (3) have a normal neuro­
logical examination and normal intelligence, and (4) show elec­
troencephalogram results that have normalized with treatment.
Epileptic women should be advised to daily take a 4-mg
folic acid supplement. Even so, it is not entirely clear that folate
supplementation reduces the fetal malformation risk in pregnant
women taking anticonvulsant therapy. In one case-control study,
Kjer and associates (2008) reported that the congenital abnor­
mality risk was reduced by maternal folate supplementation in
fetuses exposed to carbamazepine, phenobarbitl, phenytoin, and
primidone. Conversely, from the United Kingdom Epilepsy and
TABLE 8-2. Fi rst-Trimester . ntiepileptic Monothera py
a n d the Associated Major Malformation Risk
Antiepileptic (n)
Malformations
(%)
U nexposed controls (442)
La motrig i n e ( 1 562)
Ca rba m aze p i n e ( 1 033)
P h enyto i n (4 1 6)
Leveti ra ceta m (450)
Top i ra m ate (359)
Va l p roate (323)
P h e n obarb ita l ( 1 99)
Oxca rbaze p i ne ( 1 82)
G a ba penti n ( 1 45)
Clo nazepa m (64)
1 .1
2.0
3.0
2.9
2.4
4.2
9.3
5.5
2.2
OJ
3.1
Relative Risk
(95% CW
Reference
1 .8
2.7
2.6
2.2
3.8
9.0
5.1
2.0
0.6
2.8
(0.7-4 .6)
( 1 .0-7.0)
(0.9-7.4)
(0.8-6.4)
( 1 .4- 1 0.6)
(3.4-23.3)
(1 .8- 1 4.9)
(0.5-7.4)
(0.07-5.2)
(0.5- 1 4.8)
a R i s k com pared with t h at of the u nexposed refere n ce
pop u l ation of nonepi l e pt i c women.
Data from Hernandez-Oraz 5, Smith CR, Shen A., et al: Compara­
n
=
n u m be r of exposed i nfa nts.
tive safety of a ntiepileptic drugs d u r i ng preg nancy. Neurology
78:1 692, 20 1 2.
P reconceptiona I C a re
Pregnancy Register, Morrow and coworkers (2009) compared
fetal outcomes of women who received preconceptional folic acid
with those who did not receive it until later in pregnancy or not
at all. In this study, a paradoxical increse in the number of major
congenital malformations was observed in the group who received
preconceptional folate. hese investigators concluded that folate
metabolism may be only a part of the mechanism by which mal­
formations are induced in women taking these medications.
• Immunizations
Preconceptional counseling includes assessment of immunity
against common pathogens. Also, depending on health status,
travel plans, and time of year, other immunizations may be
indicated as discussed in Chapter 9 (Table 9-7, p. 1 72). Vac­
cines that contain toxoids such as tetanus are suitable before
or during gestation. Also, those containing killed bacteria or
viruses-such as inluenza, pneumococcus, hepatitis B, menin­
gococcus, and rabies vaccines-are not associated with adverse
fetal outcomes and are not contraindicated preconceptionally
or during pregnancy. Conversely, live-virus vaccines are not
recommended during pregnancy. Examples are vaccines against
varicella-zoster, measles, mumps, rubella, polio, chickenpox,
and yellow fever. Moreover, 1 month or longer should ideally
pass between vaccination and conception attempts. That said,
inadvertent administration of measles, mumps, rubella (MMR)
or varicella vaccines during pregnancy should not generally be
considered indications for pregnancy termination. Most reports
indicate that the fetal risk is only theoretical. Immunization to
smallpox, anthrax, and other bioterrorism diseases should be
discussed if clinically appropriate (Chap. 64 , p. 1 228).
With some infections, vaccines are unavailable. One recent
example is the Zika virus (Brasil, 20 1 6) . For this virus, the
CDC has issued travel advisories for pregnant women (Petersen,
20 1 6; Schuler-Faccini, 20 1 6) .
GENETIC DISEASES
he CDC (20 1 6) estimates that 3 percent of neonates born
each year in the United States will have at least one birth defect.
Importantly, such defects are the leading cause of infant mor­
tality and account for 20 percent of deaths. The benefi t s of
preconceptional counseling usually are measured by compar­
ing the incidence of new cases before and after initiation of a
counseling program. Congenital conditions that clearly beneit
from patient education include neural-tube defects, phenylke­
tonuria, thalassemias, and other genetic diseases more common
in individuals of Eastern European Jewish descent.
• Family History
Pedigree construction using the symbols shown in Figure 8-2 is
the most thorough method for obtaining a family history as a
part of genetic screening. he health and reproductive status of
each "blood relative" should be individually reviewed for medi­
cal illnesses, mental retardation, birth defects, infertility, and
pregnancy loss. Certain racial, ethnic, or religious backgrounds
may indicate elevated risk for specific recessive disorders.
Although most women can provide some information
regarding their history, their understanding may be limited.
For example, several studies have shown that pregnant women
often fail to report a birth defect in the family or they rep ort it
incorrectly. hus, any disclosed defect or genetic disease should
be conirmed by reviewing pertinent medical records or by con­
tacting afected relatives for additional information.
• Neural-Tube Defects
he incidence of neural-tube defects (NTDs) is 0.9 per 1 000
live births, and they are second only to cardiac anomalies as the
most frequent structural fetal malformation (Chap. 1 3, p. 270) .
Some NTDs, as well as congenital heart defects, are associated
with speciic mutations. One example is the 677C -+ T substitu­
tion in the gene that encodes methylene tetrahydrofolate reduc­
tase. For this and similar gene defects, the trial conducted by
the Medical Research Council Vitamin Study Research Group
( 1 99 1 ) showed that preconceptional folic acid therapy signifi­
cantly reduced the risk for a recurrent NTD by 72 percent. More
importantly, because more than 90 percent of neonates with
NTDs are born to women at low risk, Czeizel and Dudas ( 1 992)
showed that supplementation reduced the a priori risk of a irst
NTD occurrence. It is currently recommended, therefore, that all
women who may become pregnant take daily 400 to 800 j1g of
folic acid orally before conception and through the irst trimester
(U.S Preventive Services Task Force, 2009) . Folate fortiication
of cereal grains has been mandatory in the United States since
1 998, and this practice has also resulted in decreased neural-tube
defect rates (Williams, 20 1 5) . Despite the demonstrated benefits
of folate supplementation, only half of women have taken folic
acid supplementation periconceptionally (de Jong-van den Berg,
2005; Goldberg, 2006) . The strongest predictor of use appears
to be consultation with a health-care provider before conception.
• Phenylketonuria
More than 600 mutations have been identified in the phenyl­
alanine hydroxylase gene. The inherited defect in phenylalanine
metabolism exempliies diseases in which the fetus may not be
at risk to inherit the disorder but may be damaged by maternal
disease. Specifically, mothers with phenylketonuria (PKU) who
eat an unrestricted diet have abnormally high blood phenylala­
nine levels. his amino acid readily crosses the placenta and can
damage developing fetal organs, especially neural and cardiac
tissues (Table 8-3) .
TABLE 8-3. F requency o f Co m p l i cations i n t h e Offs p r i n g
o f Women w i t h U ntreated P henyl keto n u ria
Complication
Sponta neous a bortion
Developmental del ays
Microcep haly
Congenital heart d i sease
Feta l-g rowth restriction
Frequency (%)
24
92
73
12
40
Data from American Academy of Ped iatrics: Mate n a l
phenyl keto n u ria, Ped iatrics 2 008 \ug; 1 2 2 (2):44 5-449.
1 49
1 50
P reconcept i o n a l a n d P renata l C a re
o
o
o
O
Male
Marriage
0---0
Female
Sex u nspecified
Extramarital mati ng
Divorce
Num ber of children
of sex indicated
Consanguineous
mating
Affected
Monozygotic twi ns
Heterozygotes for
autosomal trait
Dizygotic twi ns
Carrie r of X - l i n ked
recessive trait
Proband
Twins of un known
zygosity
Deceased i nd ividual
Numberi ng i ndividuals
i n pedigrees
Prenatal death
Miscarriage
II
3
P roband is II
-
2
Adopted i nto a family
No offspring
Adopted out of a fam ily
F I G U R E 8-2 Sym bols u sed for ped ig ree construction . (Mod ified with permission from Thom pson MW, Mcin nes RR, H u nti ngton FW (eds):
Genetics i n Medicine, 5th ed. Ph iladelph ia, Saunders, 1 99 1 .)
With appropriate preconceptional counseling and adherence
to a phenylalanine-restricted diet before pregnancy, the inci­
dence of fetal malformations is dramatically reduced (Camp,
20 1 4; Vockley, 20 1 4) . Therefore, the phenylalanine concen­
tration is ideally normalized 3 months before conception and
then maintained throughout pregnancy (American College of
Obstetricians and Gynecologists, 20 1 7b) . The target phenylala­
nine blood concentration is 1 20 to 360 �mol/L (Camp, 20 1 4) .
• Thalassemias
hese disorders of globin-chain synthesis are the most common
single-gene disorders worldwide (Forget, 20 1 3; Vichinsky,
20 1 3) . As many as 200 million people carry a gene for one
of these hemoglobinopathies, and hundreds of mutations are
known to cause thalassemia syndromes (Chap. 56, p. 1 084) . In
endemic areas such as Mediterranean and Southeast Asian coun­
tries, counseling and other prevention strategies have reduced
the incidence of new cases by up to 80 percent (Cao, 20 1 3) .
The American College o f Obstetricians and Gynecologists
(20 1 5a) recommends that individuals of high-risk ancestry
be ofered carrier screening to allow them informed decision
making regarding reproduction and prenatal diagnosis. One
method of early prenatal diagnosis is preimplantation genetic
diagnosis (PGD), which is coupled with assisted reproduc­
tive technologies. Described in Chapter 14 (p. 295) , PGD is
P recon ce ptio n a l Ca re
available for patients at risk for certain thalassemia syndromes
(Kuliev, 20 1 1 ) .
• Individuals of Eastern European
Jewish Descent
Most individuals of Jewish ancestry in North America are
descended from Ashkenazi Jewish communities and are at
increased risk for having ofspring with one of several auto­
somal recessive disorders. These include Tay-Sachs disease,
Gaucher disease, cystic ibrosis, Canavan disease, familial dys­
autonomia, mucolipidosis IV, Niemann-Pick disease type A,
Fanconi anemia group C, and Bloom syndrome. The American
College of Obstetricians and Gynecologists (20 1 6c, 20 1 7a) rec­
ommends preconceptional counseling and screening for these
in this population. Carrier frequency and features of these con­
ditions are discussed in Chapter 14 (p. 290) .
REPRODUCTIVE H ISTORY
During preconceptional screening, information is sought
regarding infertility; abnormal pregnancy outcomes that may
include miscarriage, ectopic pregnancy, and recurrent preg­
nancy loss; and obstetrical complications such as cesarean
delivery, preeclampsia, placental abruption, and preterm deliv­
ery (Stubblefield, 2008) . As discussed in Chapter 35 (p. 646) ,
details involving a prior stillbirth are especially important. For
example, Korteweg and associates (2008) identiied chromo­
somal abnormalities in 1 3 percent of stillborns who underwent
karyotyping. Reddy and colleagues (20 1 2) confirmed that
chromosomal micro array analysis (CMA) yielded better detec­
tion of genetic abnormalities than did standard karyotyping,
primarily because nonviable tissue can be used for the analy­
sis. CMA is described and illustrated in Chapter 1 3 (p. 27 1 ) .
Identiication o f a genetic abnormality i n a stillborn can help
determine the recurrence risk and aid in the preconceptional or
prenatal management in subsequent pregnancies.
PARENTAL AGE
• Maternal Age
Women at both ends of the reproductive-age spectrum have
unique outcomes to be considered. First, according to the CDC,
in 20 1 0, 3.4 percent ofbirths in the United States were in women
between the ages of 1 5 and 1 9 years (Martin, 20 1 2) . These ado­
lescents are at increased risk for anemia, preterm delivery, and
preeclampsia compared with women aged 20 to 35 years (Usta,
2008) . he incidence of sexually transmitted diseases-com­
mon in adolescents-is even higher during pregnancy (Nicco­
lai, 2003) . Unfortunately, because most of their pregnancies are
unplanned, adolescents rarely seek preconceptional counseling.
Conceptions after age 35 currently comprise approximately
1 5 percent of pregnancies in the United Stares (Martin, 20 1 2) .
B y contrast, these older women are more likely t o request
preconceptional counseling, either because of postponed
pregnancy with a desire to optimize outcomes or because of
plans to undergo infertility treatment. Some studies-includ­
ing data from Parland Hospital presented in Figure 8-3-
18
16
14
.�
12
0
C
8
)
)
::
) 10
0
.
m
)
u
..
6
4
2
0
Previa
L_=�������===!�
Abruption
20-24
25-29
30-34
Maternal age
>
35
F I G U R E 8-3 I n c idence of selected preg n a ncy c o m p l icatio n s i n
relatio n t o m aterna l a g e a mo n g 295,667 wo m e n del ivered a t
Parkland Hospita l.
indicate that ater age 35, the risks for obstetrical complications
and for perinatal morbidity and mortality rise (Cunningham,
1 995; Waldenstrom, 201 5). he older woman who has a chronic
illness or who is in poor physical condition usually has readily
apparent risks. For rhe physically fit woman without medical prob­
lems, however, the risks are much lower than previously reported.
Overall, the maternal mortality rate is higher in women aged
35 and older. Compared wirh women in rheir 20s, women aged
35 to 39 are 2.5 times more likely and women aged 40 or older
are 5.3 times more likely to sufer pregnancy-related mortality
(Geller, 2006) . Creanga and coworkers (20 1 5) analyzed preg­
nancy-related deaths in the United States for 2006 through
20 1 0. Although women older than 35 years contributed less
than 1 5 percent of all live births, they constituted 27 percent
of maternal deaths. For the fetus, maternal age-related risks pri­
marily stem from: ( 1 ) indicated preterm delivery for maternal
complications such as hypertension and diabetes, (2) spontane­
ous preterm birth, (3) fetal growth disorders related to chronic
maternal disease or multifetal gestation, (4) fetal aneuploidy, and
(5) pregnancies resulting from assisted reproductive technology.
Assisted Reprod u ctive Tech n o log ies
Recall that older women have subfertility problems. And
although the incidence of dizygotic twinning increases with
maternal age, the more important cause of multifetal gestation
in older women follows the use of assisted reproductive technol­
ogy (ART) and ovulation induction. Indeed, according to the
CDC, 30 to 40 percent of all multifetal gestations in the United
States in 20 1 2 were conceived with the use of ART (Sunderan,
20 1 5) . Morbidity and mortality with multifetal pregnancies
stem from preterm delivery. Other obstetrical morbidities, such
as placenta previa, abruption, and preeclampsia, are also risks
associated with these conceptions (Lukes, 20 1 7; Qin, 20 1 6) .
Finally, experience has accrued that links ART t o higher
major congenital malformation rates. Davies and colleagues
(20 1 2) reported that of 308,974 births in South Australia, 8.3
percent of neonates conceived by ART had major birth defects.
1 51
1 52
P reconceptio n a l a n d P renata l Ca re
In this analysis, after adjustment for maternal age and other risk
factors, intracytoplasmic injection continued to be associated
with a signiicantly elevated risk for malformations, but in vitro
fertilization did not.
• Paternal Age
Parental history and experiences-paternal and maternal-can
exert efects through epigenomic information not contained in the
DNA sequence. Examples include variations in sperm and oocyte
cytosine methylation and other mechanisms (Cedars, 20 1 5 ;
Lane, 20 1 4) . Perhaps one example is the possible link between
increasing paternal age and complex neuropsychiatric conditions
(Malaspina, 20 1 5) . Finally, the incidence of genetic diseases in
ofspring caused by new autosomal-dominant mutations in older
men is increased. Still, the incidence is low (Chap. 1 3, p. 265).
Accordingly, targeted sonographic examination performed solely
for advanced maternal or paternal age is controversial.
SOCIAL H ISTORY
• Recreational Drugs and Smoking
Fetal risks associated with alcohol, marijuana, cocaine, amphet­
amines, and heroin are discussed in Chapter 1 2 (p . 239) . he
first step in preventing drug-related fetal risk is an honest assess­
ment of use by the patient (American College of Obstetricians
and Gynecologists, 20 1 7 c) . Toward this end, questioning
should be nonjudgmental. Screening for at-risk drinking can
be accomplished using several validated tools. One is the well­
studied TACE questions (American College of Obstetricians
and Gynecologists, 20 1 3) . This is a series of four questions con­
cerning .olerance to alcohol, being 4nnoyed by comments about
their drinking, attempts to fut down, and a history of drinking
early in the morning-the fye opener.
In a Canadian study of more than 1 000 postpartum
patients, Tough and coworkers (2006) found that a high per­
centage of women reported alcohol use concurrent with con­
ception attempts. Specifically, nearly half of those planning for
pregnancy reported a mean of 2.2 drinks daily during early
gestation and before they recognized their pregnancy. Of note,
Bailey and associates (2008) found that rates of binge drinking
and marijuana use by men were unafected by their partner's
pregnancy. The frequency and pattern of such behaviors clearly
underscore the opportunity for preconceptional counseling.
Currently 20 million women in the United States smoke
cigarettes (Centers for Disease Control and Prevention, 20 1 4 ) .
Smoking i n pregnancy has been consistently associated with
numerous adverse perinatal outcomes, listed in Chapter 1 2 (p.
249) . These risks are largely mitigated by cessation before preg­
nancy, highlighting the importance of screening for tobacco
use in the preconceptional period and during prenatal care as
outlined in Chapter 9 (p. 1 6 1 ) .
• Environmental Exposures
Contact with environmental substances is inescapable. Thus, it
is fortunate that only a few agents have been shown to cause
adverse pregnancy outcomes (Windham, 2008) . Exposures to
infectious diseases have myriad deleterious efects, and these are
detailed in Chapters 64 and 65 . Likewise, contact with some
chemicals may impart signiicant maternal and fetal risks. As
discussed in Chapters 9 and 1 2 (pp. 1 70 and 244), excess expo­
sure to methyl mercury or lead is associated with neurodevel­
opmental disorders.
In the past, some concerns were raised over common every­
day exposure to electromagnetic iels such as those emanated by
high-voltage power lines, electric blankets, microwave ovens,
and cellular phones. Fortunately, no human or animal evidence
links these and adverse fetal outcomes (Robert, 1 999) . he
efects of electrical shock are discussed in Chapter 47 (p. 930) .
• Diet
Pica is the craving for and consuming of ice, laundry starch, clay,
dirt, or other nonfood items. It should be discouraged due to its
inherent replacement of healthul food with nutritionally empty
products (Chap. 9, p. 1 74) . In some cases, it may represent an
unusual physiological response to iron deficiency. Many vegetar­
ian diets are protein deficient but can be corrected by increas­
ing egg and cheese consumption. Anorexia and bulimia increase
maternal risks of nutritional deiciencies, electrolte disturbances,
cardiac arrhythmias, and gastrointestinal pathology (Becker,
1 999) . s discussed in Chapter 6 1 (p. 1 1 80), pregnancy-related
complications with these disorders include greater risks of low
birthweight, smaller head circumference, microcephaly, and
small-for-gestational-age newborns (Kouba, 2005) .
In contrast to these perinatal morbidities, obesiy is linked
with several maternal complications. As discussed in Chapter 48
(p. 939) , these include preeclampsia, gestational diabetes, labor
abnormalities, cesarean delivery, and operative complications
(American College of Obstetricians and Gynecologists, 20 1 5b) .
Obesity also appears to be associated with a range of structural
fetal anomalies (Stothard, 2009) .
• Exercise
Conditioned pregnant women usually can continue to exercise
throughout gestation (American College of Obstetricians and
Gynecologists, 20 1 7d) . As discussed in Chapter 9 (p. 1 70) , no
data suggest that exercise is harmful during pregnancy. One
caveat is that as pregnancy progresses, balance problems and
joint relaxation may predispose to orthopedic injury. A woman
is advised not to exercise to exhaustion, and she should aug­
ment heat dissipation and fluid replacement. Further avoid­
ances include prolonged supine position, activities requiring
good balance, and extreme weather conditions.
• Intimate Partner Violence
Pregnancy can exacerbate interpersonal problems and is a time of
elevated risk from an abusive partner. According to the American
College of Obstetricians and Gynecologists (20 1 2) , approximately
324,000 pregnant women are abused each year. As discussed in
Chapter 47 (p. 925), intimate partner violence has been asso­
ciated with greater risk for several pregnancy-related complica­
tions, including hypertension, vaginal bleeding, hyperemesis,
preterm delivery, and low-birthweight neonates (Silverman,
P reco n ce ptio na l Ca re
2006) . Because domestic violence can escalate during pregnancy,
even to the point of homicide, the preconceptional period pro­
vides an ideal time for screening and if indicated, intervention
(Cheng, 20 1 0) . s detailed in Chapter 9 (p. 1 62) , the American
College of Obstetricians and Gynecologists (20 1 2) provides rec­
ommendations and resources for screening both pregnant and
nonpregnant women for domestic violence.
SCREENING TESTS
Certain laboratory tests may help assess the risk for and pre­
vent some pregnancy complications. hese include basic tests
that are usually performed during prenatal care and are enu­
merated in Chapter 9. More speciic tests may assist evalua­
tion of women with certain chronic medical diseases. Examples
of some chronic diseases that ideally would be assessed before
conception are highlighted in Table 8-4. With several of these,
optimizing maternal condition before conception will improve
pregnancy outcomes. Cox and coworkers ( 1 992) reviewed
pregnancy outcomes in 1 075 high-risk women who received
such evaluation. hey reported that the 240 women with
hypertension, asthma, or renal, thyroid, or cardiac disease had
better outcomes compared with the outcomes from their prior
pregnancies.
TABLE 8-4. Selected P reconceptiona l Cou ns e l i n g Top ics
Condition
Reference Cha pter
Enviro n menta l
expos u re
C h a p. 9, p. 1 70
C h a p. 1 2, p. 244
Abnormal
weight
C ha p. 48, p. 93 6
C h a p. 6 1 , p. 1 1 80
Ca rd i ovascu l a r
d isease
Cha p. 49, p. 95 1
Cha p. 1 2, pp. 24 1 ,
247
C h ronic
hyperte nsion
C h a p. 5 0, p. 976
AsthMa
C h a p. 5 1 , p. 988
Th rom boph i l ia
C h a p. 5 2, p. l 006
Ren a l d : sease
Cha p. 53, p. 1 02 5
C h a p. 1 2, p. 24 1
Ga stroi ntest i n a l
d isease
Cha p. 54, p. 1 05 0
C h a p. 1 2, pp. 242,
244
Hepato b i l i a ry
d i sea se
Chap. 55, p. 1 064
Hematological
d i sease
Cha p. 5 6, p. l 075
Recommendations for Preconceptional Counseli ng
Methyl mercury: Avoid s h a rk, swordfi sh, ki ng macke rel, and tile fi s h. I ngest no m o re
than 1 2 o u nces or 2 servi n g s of ca n n ed tuna a n d no m o re tha n 6 o u n ces of
a l bacore per week.
Lead: B lood lea d testing if a risk factor is i dentified; t reat if i n d icated a ccord i ng to
reco m m endations.
Calcu l ate BMI yea rly from Fig u re 48- 1 , p. 937
BMI .25 kglm2: Cou nsel o n d i et. Test for dia betes a n d m eta bo l i c synd rome if
i nd i cated. Consider we i g h t 1 05s prior to co ncepti on.
BMI � 7 8. 5 kglm2: Assess for eati n g d isorder.
Co u nsel on ca rd iac risks d u ri ng p reg n a ncy; d iscuss situations i n which preg n a n cy
is contra i nd i cated . Opti m ize c a rd i a c fu n ction. Di scuss med ication tera toge n i c i ty
(wa rfa r i n , ACE i n h ' bitor, A RB) a nd, if poss i ble, switch to less d a ng e rous agent
when conception p l a n ned . Ofer g enetic co u n s e l i n g to t h ose with co ngen ita l
ca rd iac a noma l ies (Ta b l e 49-4, p. 953).
Cou n sel on s pecifi c risks d u ri ng preg n a ncy. Assess those with l o n g-sta n d i ng
HTN for ventricu l a r hypertrophy, retinopathy, and ren a ! d isease. O pti m ize
b lood p ress u re co tro l . If med ications i nd icated, select or switch to an agent
a p p ropriate for preg n a n cy.
Cou n se l on asthma risks d u ri n g p reg n a n cy. Optim ize p u l m o n a ry fu n ction
preconceptiona l ly. Treat wo m e n with pha rmacologica l step th era py for c h ro n i c
asthma.
Questi o n for perso n a l o r fa m i ly h i story of thro m botic events o r recu rrent poor
p reg na n cy o utcomes. If a t h ro m boph i l ia is fou n d or known, cou nsel and offe r
a p p ropriate a nticoag u l ation reg i men.
Cou n sel on specific risks d u ri n g p reg n a ncy. Opti m ize b l ood press u re control
before conception . Cou n s e l wom e n ta king ACE i n h i bi tors and A R Bs a bolJ t
teratog e n i c ity a n d the need to switch agents before preg na n cy.
Inlammatory bowel disease: Co u n sel afected women on su bferti l ity r i s ks and risks
of adverse preg na ncy o utcom es. Discuss teratoge n icity of methotrexate and the
other i m n u nomod u lators. Offer effective contraception d u ri n g their u se and
switch agents, if poss i ble, before conception.
Hepatitis B: Vaccinate a l l h ig h-ri s k wo men befo re conceptio n (Ta ble 9-7, p. 1 72) .
Co u nsel c h ro n i c carriers on tra n s m ission prevention to pa rtners a nd fet us. Treat
if i n d i cated.
Hepatitis C: Screen h i g h-risk wom en. Cou nsel affected ,fom e n o n r i s ks of
d i sease and tra n s m i ssion . If treat m e nt i nd icated, d iscuss ram i fi cations a n d
a p p ropriate ness of preg n a n cy.
Iron-deficiency anemia: I ro n su pp l e m e ntation .
Sickle-cell dis ease: Screen a l l b la c k women. Cou n sel those with trait o r d isease. Test
partner if desi red .
Thalassemias: Scree n women of Southeast Asian or Med iter ra nean a ncestry.
(continued)
1 53
1 54
P reconce pti o n a l a n d P renata l Care
TABLE 8-4. Conti n ued
Condition
Reference Chapter
Recommendations for Preconceptional Counseling
Dia betes
Cha p. 5 7, p. 1 1 04
Thyro id d i sease
Cha p. 5 8, p. 1 1 1 8
Con n ective
tissue d i sease
Cha p. 5 9, p. 1 1 3 8
Chap. 1 2, p. 24 1
Psych iatric
d i so rders
Cha p. 6 1 , p. 1 1 7 5
Neu rological
d i so rd ers
Dermatolog ica l
d i sease
Cancer
C h a p. 60, p. 1 1 5 9
O pt i m ize g lycem i c control t o m i n i m ize teratoge n i city o f hyperg lyce m i a . Eva l uate
for end-org a n d a m age such as ret i n opathy, neph ropathy, hypertension, a n d
others. D i sconti n u e A C E i n h i b ito rs.
Screen t h ose with thyro i d d i sease sym pto ms. E n s u re i od i ne-suficient d iet.
Treat overt hyper- or hypothyro i d i s m . Co u n sel on risks to preg na ncy
o utcome.
RA: Co u n se l o n fla re risk after preg n a n cy. Disc u s s methotrexate and l efl u n o m i d e
teratog e n i c i ty, a s we l l as poss i b l e effects o f oth e r i m m u n omod u lators.
Switch these agents before co nception . Sto p N SA I Ds by 2 7 weeks'
gestation .
SLE: Cou n sel on risks d ur i ng preg na ncy. O pt i m ize d i sease before conception.
D i sc u ss mycophenolate m ofeti l a nd cyclophos p h a m i d e teratoge n icity a s wel l
a s poss i b l e effects o f n ewer i m m u n om od u l ators. Switch these agents before
concept i o n.
Depression: Screen for sym ptoms of d e p ression. Cou n sel on r i s ks of t reatment a nd
of u nt reated i l l ness a n d the h i g h risk of exacerbat i o n d u ri n g preg nancy a n d the
puerperi u m .
Seizure disorder: Opt i m ize seizu re control u s i ng m o n othera py if pos s i b l e.
I nfectious
d i seases
C h a p. 64, p. 1 209
STDs
C h a p. 65, p. 1 23 5
Cha p. 1 2, p. 245
C h a p. 63, p. 1 1 92
D i sc u ss i sotreti n o i n a nd etreti nate teratog e n icity a n d effective contraception
d u ri n g the i r u se; switch agents before concept i o n .
Cou nsel on ferti l i ty preservation opt i o n s before ca ncer th erapy a n d on decreased
fert i l ity fol lowi ng certa i n age nts. D i scuss ap propriateness of preg na n cy
ba la nced with n eed fo r ongoing cancer therapy a nd prog nosis of the d i sease
state.
Influenza: Vacci nate a l l women who wi l l be preg n a nt d u ri ng fl u sea so n . Vacci nate
h ig h-ri s k wo m e n prior to fl u seaso n .
Malaria: Cou n sel to avo i d travel t o e n d e m i c a reas d u ri n g concepti o n . If u n a b le,
offer effective contraception d u ri ng t rave l or provide chemoprophylaxis for
t h ose pla n n i ng preg nancy.
Zika virus: See t ravel restrictions by CDC.
Rubella: Screen fo r r u be l l a i m m u n ity. If n o n i m m u ne, vacci nate a n d cou n sel o n the
n eed for effective contraception d u ri n g the su bseq uent m o nt h.
Tdap: tetanus, diphtheria, pertussis: U pdate vacc i n ation i n a l l reprod uctive-ag ed
wom e n .
Varicella: Q uestion reg a rd i n g i m m u n ity. If non i m m u ne, vacc i nate.
Gonorrhea, syphilis, chlamydial infection: Screen h i g h-risk women a n d t reat a s
i n d i cated.
HIV: Screen at-risk women . Cou nsel afected women on risks d u ri n g preg na ncy
a n d on pe ri natal t ra n s m i ssion . D i sc u ss i n itiation of treatment before preg nancy
to decrease t ra ns m ission risk. Offe r effective contraception to those n ot desi r i ng
concept i o n .
HPV' P rovid e Pap smear scree n i ng per g u idel i n es (Ch a p. 63, p. 1 1 93) . Vacci nate
c a n d i date patie nts.
HSV: P rovide sero l og ical scree n i ng to a sym ptomatic women with affected
pa rtners. Cou n sel affected women on risks of peri nata l t ra n s m i ssion a n d on
preventative meas u res d u ri n g the th i rd tri mester a n d la bor.
ACE a n g i ote n s i n -convert i n g e nzym e; ACOG American Col lege of Obstet r i c i a n s a n d Gynecologists; ARB a n g iote n s i n ­
receptor blocker; B M I body mass i nd ex; C DC Cente rs for D i sease Control a n d P revention; H IV h u m a n i m m u no­
d eficiency vi rus; H PV h u ma n pa p i l l o mavi rus; H SV h erpes s i m plex vi rus; HTN hyperte nsion; NSAID no nstero i d a l
a nt i i nfl a m m atory d rug; RA rheu m atoid a rth ritis; SLE syste m i c l u pus erythematosu s; STD sexua l ly t ra n s m itted d i sease.
Data from Jack BW, Atras h H, Coon rod DV, et a l : The c l i n i ca l content of preconcept i o n ca re: a n overview a n d pre pa ration of
t h i s su pplement, Am J Obstet Gyneco l . 2008 Dec; 1 99(6 S u ppl 2) :5266-S279.
=
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P reconce ptiona l Care
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1 57
C H A PT E R 9
P re n ata l Ca re
DIAGNOSIS OF PREGNANCY. . . . . . . . . . . . . . . . . . . . . . 1 58
I N ITIAL PRENATAL EVALUATION . . . . . . . . . . . . . . . . . . 1 59
SUBSEQUENT PRENATAL VISITS . . . . .
.
. . . . . . . . . . . . . 1 64
N UTRITIONAL COUNSELING . . . . . . . . . . . . . . . . . . . . . . 1 65
COMMON CONCERNS . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 70
The borderline between health and disease is less distincty
marked during gestation, and therore, it accordingy
becomes necessary to keep pregnant patients under strict
supervision, and to be constanty on the alertor the appear­
ance of untoward symptoms.
-J. Whitridge Williams ( 1 903)
s emphasized above by Williams, prenatal care is important.
According to the merican Academy of Pediatrics and the Amer­
ican College of Obstetricians and Gynecologists (20 1 7) a com­
prehensive antepartum program is deined as: "a coordinated
approach to medical care, continuous risk assessment, and
psychological support that optimally begins before conception
and extends throughout the postpartum period and intercon­
ceptional period. "
Figure 9- 1 , 6 to 7 percent of women in this country have late
or no prenatal care. In 20 1 4, the percentages of non-Hispanic
white, Hispanic, and African-American women who received
inadequate or no prenatal care were 4.3, 7 . 5 , and 9.7, respec­
tively (Child Trends, 20 1 5) .
he Centers for Disease Control and Prevention (CDC)
(2000) analyzed birth certificate data and found that half of
women with delayed or no prenatal care wanted to begin care
earlier. Barriers to care varied by social and ethnic group, age,
and payment method. he most common reason cited was late
recognition of pregnancy by the patient. The second most com­
monly cited obstacle was lack of money or insurance. he third
was inability to obtain an appointment.
• Prenatal Care Efectiveness
Care designed during the early 1 900s focused on lowering the
extremely high maternal mortality rate. Prenatal care undoubt­
edly contributed to the dramatic decline in this mortality rate
from 690 deaths per 1 00,000 births in 1 920 to 50 per 1 00 ,000
8
2
PRENATAL CARE IN THE U N ITED STATES
Almost a century after its introduction, prenatal care has
become one of the most frequently used health services in
the United States. In 200 1 , there were approximately 50 mil­
lion prenatal visits. The median was 1 2. 3 visits per pregnancy,
and many women had 1 7 or more visits. Still, as seen from
•
•
Births in all states
Births in states using the 1 989 birth certificate/revision
Births in states using the 2003 birth certificate/revision
o ---�
•
1 990
1 993 1 996 1 999 2002
2005
2008 20 1 1
20 1 4
Year
FIGURE 9-1 Percentage of birt h s to mothers who received late
or no prenata l ca re-U n ited States, 1 990-20 1 4. (Data from Ch i ld
Trends, 20 1 5.)
1 58
P reconceptional a n d P renatal Ca re
by 1 9 5 5 (Loudon, 1 992) . And, the low current maternal mor­
tality rate of 10 to 1 5 per 1 00,000 is likely associated with
the high utilization of this care (Xu, 20 1 0) . Indeed, data from
1 998 to 2005 from the Pregnancy \10rtality Surveillance Sys­
tem identified a ivefold increased risk for maternal death in
women who received no prenatal care (Berg, 20 1 0) .
Other reports also attest t o prenatal care eicacy. I n a study
of almost 29 million births, the risk for preterm birth, still­
birth, early and late neonatal death, and infant death rose lin­
early with decreasing prenatal care (Partridge, 20 1 2) . Similarly,
Leveno and associates (2009) found that a significant decline
in preterm births at Parkland Hospital correlated closely with
increased use of prenatal care by medically indigent women.
Moreover, National Center for Health Statistics data showed
that women with prenatal care had an overall stillbirth rate of
2 . 7 per 1 000 compared with 1 4. 1 per 1 000 for women without
this care (Vintzileos, 2002) .
Evaluating the format of care, Ickovics and coworkers (20 1 6)
compared individual prenatal care and group prenatal care. he
latter provided traditional pregnancy surveillance in a group set­
ting with special focus on support, education, and active health­
care participation. Women enrolled in group prenatal care had
significantly better pregnancy outcomes. Carter and colleagues
(20 1 6) cited similar results. Childbirth education classes are also
reported to result in better pregnancy outcomes (Afshar, 20 1 7) .
Adolescent pregnancies carry special risk, and guidelines have
been developed that focus on this subgroup (Fleming, 20 1 5) .
Few data are available t o recommend the practice o f ofering
tangible incentives to improve prenatal care attendance (Till,
20 1 5) .
DIAGNOSIS OF PREGNANCY
Pregnancy is usually identifi e d when a woman presents with
symptoms and possibly a positive home urine pregnancy test
result. Typically, these women receive conirmatory testing
of urine or blood for human chorionic gonadotropin (hCG ) .
Further, presumptive signs or diagnostic indings of pregnancy
may be found during examination. Sonography is often used,
particularly if miscarriage or ectopic pregnancy is a concern.
• Symptoms and Signs
Amenorrhea in a healthy reproductive-aged woman who previ­
ously has experienced spontaneous, cyclical, predictable men­
ses is highly suggestive of pregnancy. Menstrual cycles vary
appreciably in length among women and even in the same
woman (Chap. 5, p. 8 1 ) . hus, amenorrhea is not a reliable
pregnancy indicator until 1 0 days or more after expected
menses have passed. Occasionally, uterine bleeding that mim­
ics menstruation is noted after conception. During the irst
month of pregnancy, these episodes are likely the consequence
of blastocyst implantation. Still, irst-trimester bleeding should
generally prompt evaluation for an abnormal pregnancy.
Of other symptoms, maternal perception of fetal move­
ment depends on factors such as parity and habitus. In gen­
eral, after a irst successful pregnancy, a woman may irst
perceive fetal movements between 1 6 and 1 8 weeks' gestation.
A primigravida may not appreciate fetal movements until
approximately 2 weeks later. At about 20 weeks, depending
on maternal habitus, an examiner can begin to detect fetal
movements.
Of pregnancy signs, changes in the lower reproductive tract,
uterus, and breasts develop early. These are described in detail
in Chapter 4 (p. 49) .
• Pregnancy Tests
Detection of hCG in maternal blood and urine is the basis for
endocrine assays of pregnancy. Syncytiotrophoblast produces
hCG in amounts that increase exponentially during the irst
trimester following implantation. A main function of hCG is
to prevent involution of the corpus luteum, which is the prin­
cipal site of progesterone formation during the irst 6 weeks of
pregnancy.
With a sensitive test, the hormone can be detected in mater­
nal serum or urine by 8 to 9 days after ovulation. he doubling
time of serum hCG concentration is 1 .4 to 2.0 days. As shown
in Figure 9-2, serum levels range widely and increase from the
day of implantation. They reach peak levels at 60 to 70 days.
Thereafter, the concentration declines slowly until a plateau is
reached at approximately 16 weeks' gestation.
Measurement of hCG
1 00,000
50,000
'
E 1 0 ,000
5
.
"
)
5000
c
o
5
6 7 8
9 1 0 1 1 1 2 1 3 1 4 1 5 1 6 1 7 1 8 1 9 20 21 22 23 24 25 26 27
Weeks' gestation
FIGURE 9-2 Mean concentration (95% CI) of h u m a n chorionic g o nadotro p i n (hCG) in serum of
women throug hout norm a l preg n a n cy.
his hormone is a glycoprotein
with high carbohydrate content.
he general structure of hCG is a
heterodimer composed of two dis­
similar subunits, designated a and
�, which are non covalently linked.
The a-subunit is identical to those
of luteinizing hormone (LH), fol­
licle-stimulating hormone (FSH),
and thyroid-stimulating hormone
(TSH), but the �-subunit is struc­
turally distinct among these. hus,
antibodies were developed with high
speciicity for the hCG �-subunit.
This speciicity allows its detec­
tion, and numerous commercial
Prenata l C a re
immunoassays are available for measuring serum and urine hCG
levels. Although each immunoassay detects a slightly diferent
mixture of hCG variants, its free subunits, or its metabolites,
all are appropriate for pregnancy testing (Braunstein, 20 1 4) .
Depending o n the assay used, the sensitivity for the laboratory
detection limit of hCG in serum is 1 .0 mIU/mL or even lower
(Wilcox, 200 1 ) .
False-positive hCG test results are rare (Braunstein, 2002) .
A few women have circulating serum factors that may bind
erroneously with the test antibody directed to hCG in a given
assay. The most common factors are heterophilic antibodies.
hese are produced by an individual and bind to the animal­
derived test antibodies used in a given immunoassay. Thus,
women who have worked closely with animals are more likely
to develop these antibodies, and alternative laboratory tech­
niques are available (American College of Obstetricians and
Gynecologists, 20 1 7a) . Elevated hCG levels may also reflect
molar pregnancy and its associated cancers (Chap. 20, p. 39 1 ) .
Other rare causes of positive assays without pregnancy are: ( 1 )
exogenous hCG injection used for weight loss, (2) renal fail­
ure with impaired hCG clearance, (3) physiological pituitary
hCG, and (4) hCG-producing tumors that most commonly
originate from gastrointestinal sites, ovary, bladder, or lung
(Montagnana, 20 1 1 ) .
H o m e Preg na ncy Tests
Over-the-counter pregnancy test kits have been available since
the early 1 970s, and millions are sold annually in the United
States. More than 60 such tests are available in this country
(Grenache, 20 1 5) . Unfortunately, many of these are not as
accurate as advertised Gohnson, 20 1 5) . For example, Cole and
associates (20 1 1 ) found that a detection limit of 1 2. 5 mIU/mL
would be required to diagnose 9 5 percent of pregnancies at
the time of missed menses, but they reported that only one
brand had this degree of sensitivity. Two other brands gave
false-positive or invalid results. In fact, with an hCG concentra­
tion of 1 00 mIU/mL, clearly positive results were displayed by
only 44 percent of brands. Accordingly, only about 1 5 percent
of pregnancies could be diagnosed at the time of the missed
menses. Some manufacturers of even newer home urine assays
claim > 99-percent accuracy of tests done on the day of-and
some up to 4 days before-the expected day of menses. Again,
careful analysis suggests that these assays are often not as sensi­
tive as advertised Gohnson, 20 1 5) .
• Sonographic Recognition of Pregnancy
Transvaginal sonography has revolutionized early pregnancy
imaging and is commonly used to accurately establish gesta­
tional age and conirm pregnancy location. A gestational sac-a
small anechoic luid collection within the endometrial cavity­
is the irst sonographic evidence of pregnancy. It may be seen
with transvaginal sonography by 4 to 5 weeks' gestation. A luid
collection, however, can also be seen within the endometrial
cavity with an ectopic pregnancy and is termed a pseudogesta­
tional sac or pseudosac (Fig. 1 9-4, p. 375) . Thus, further evalu­
ation may be warranted if this is the only sonographic inding,
particularly in a woman with pain or bleeding. A normal
FIGURE 9-3 Tra n svag i n a l sonog ra m of a fi rst-tri mester i ntra u ter­
ine p reg n a ncy. The dou ble deci d u a l sign is noted su rrou n d i n g the
gestationa l sac a nd is defined by the decid u a parieta l i s (white aster­
isk) a nd the decidua ca p s u l a ris (yellow asterisk). The a rrow notes the
yol k sac, a n d the crown-r u m p length of the embryo is ma rked with
mea s u r i n g ca l i pers. (Used with permission from Dr. Elysia Moschos.)
gestational sac implants eccentrically in the endometrium,
whereas a pseudosac is seen in the midline of the endometrial
cavity. Other potential indicators of early intrauterine preg­
nancy are an anechoic center surrounded by a single echogenic
rim-the intradecidual sign-or two concentric echogenic rings
surrounding the gestational sac-the double decidual sin shown
in Figure 9-3 . If sonography yields equivocal indings, the term
pregnancy of unknown location (PUL) is applied. In these cases,
serial serum hCG levels and transvaginal sonograms can help
diferentiate a normal intrauterine pregnancy from an extra­
uterine pregnancy or an early miscarriage (Chap. 1 9, p. 373) .
If the yolk sac-a brightly echogenic ring with an anechoic
center-is seen within the gestational sac, an intrauterine loca­
tion for the pregnancy is confi r med. The yolk sac can normally
be seen by the middle of the ifth week. As shown in Figure 9-3,
after 6 weeks, an embryo is seen as a linear structure imme­
diately adjacent to the yolk sac. Cardiac motion is typically
noted at this point. Up to 1 2 weeks' gestation, the crown-rump
length is predictive of gestational age within 4 days (Chap. 1 0,
p. 1 83).
IN ITIAL PRENATAL EVALUATION
Prenatal care is ideally initiated early. Major goals are to:
( 1 ) deine the health status of the mother and fetus, (2) estimate
the gestational age, and (3) initiate a plan for continued o bstet­
rical care. Typical components of the initial visit are summa­
rized in Table 9- 1 . Subsequent care may range from relatively
infrequent routine visits to prompt hospitalization because of
serious maternal or fetal disease.
• Prenatal Record
Use of a standardized record within a perinatal health-care
system greatly aids antepartum and intrapartum management.
1 59
1 60
P reconceptiona l a n d Prenata l Ca re
TABLE 9-1 . Typical Components of Routi n e P re nata l Care
Weeks
Text Referral
History
Complete
U pdated
Fi rst Visit
Chap. 9, p. 1 6 1
Physica l exa m i nation
Com plete
B l ood pressu re
Maternal weig ht
Pelvic/cervica l exa m i nation
F u n d a l h e i g ht
Feta l heart rate/feta l position
C h a p.
Chap.
Cha p.
C h a p.
Chap.
Chap.
Laboratory tests
Hematocrit or h e m og l o b i n
B lood type a nd Rh factor
A nti body screen
Pap s m e a r scree n i ng
G l ucose to l e ra nce test
Feta l a n e u pl oidy scree n i n g
N e u ra l -t u be d efect scree n i ng
Cystic fi b rosis scree n i ng
U ri n e p rote i n assess ment
U ri n e cultu re
R u bel l a serology
Syph i l i s sero l ogy
Gonococca l scree n i ng
C h l a myd i a l scree n i n g
H epatiti s B serology
H IV sero l ogy
G ro u p B streptococcus c u l t u re
Tuberc u l o s i s scree n i n g
Chap. 56, p. 1 075
Chap. 1 5, p. 30 1
C h a p. 1 5 , p. 30 1
Chap. 63, p. 1 1 93
Cha p. 5 7, p. 1 1 08
Chap. 1 4, p. 2 7 8
C h a p. 1 4, p. 283
Chap. 1 4, p. 289
C h a p. 4, p. 66
Chap. 53, p. 1 026
Chap. 64, p. 1 2 1 5
Chap. 65, p. 1 237
Chap. 65, p. 1 23 9
Chap. 6 5 , p . 1 240
Chap. 55, p. 1 064
Chap. 65, p. 1 247
Chap. 64, p. 1 220
C h a p. 5 1 , p. 996
9, p. 1 63
40, p. 7 1 1
9, p. 1 65
9, p. 1 63
9, p. 1 64
9, p. 1 65
•
•
•
•
•
•
•
1 5-20
24-28
29-41
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
A
•
•
B a a n d/o r
8 0r
8
8
8
•
•
•
•
•
•
0
•
•
•
8
0
C
0
0
C
E
a F i rst-t ri m ester a n e u p l o i dy scree n i ng may be ofe red betwee n 1 1 a n d 1 4 wee ks.
A Performed at 28 weeks, if i n d i cated.
8 Test shou l d be ofered.
C H i g h-risk wom e n s h o u l d be retested at the beg i n n i ng of t h e th i rd tri mester.
o H i g h- r i s k w o m e n s h o u l d be screened at t h e fi rst p re n ata l visit a n d aga i n i n t h e th i rd
tri mester.
E Rectova g i n a l c u lt u re s h o u l d b e o bta i n ed between 35 a n d 3 7 weeks.
HIV h u ma n i m m u n od eficiency virus.
=
Standardizing documentation allows communication and care
continuity between providers and enables objective measures
of care quality to be evaluated over time and across diferent
clinical settings (Gregory, 2006) . A prototype is provided by
the American Academy of Pediatrics and the American College
of Obstetricians and Gynecologists (20 1 7) in their Guidelines
or Perinatal Care, 8th edition.
Defi n itions
Several deinitions are pertinent to establishment of an accurate
prenatal record.
1 . Nulligravida-a woman who currently is not pregnant and
has never been pregnant.
2. Gravida-a woman who currently is pregnant or has been
in the past, irrespective of the pregnancy outcome. With the
establishment of the first pregnancy, she becomes a primi­
gravida, and with successive pregnancies, a multigravida.
3. Nullpara-a woman who has never completed a pregnancy
beyond 20 weeks' gestation. She may not have been preg­
nant or may have had a spontaneous or elective abortion(s)
or an ectopic pregnancy.
4. Primipara-a woman who has been delivered only once of a
fetus or fetuses born alive or dead with an estimated length
of gestation of 20 or more weeks. In the past, a 500-g birth­
weight threshold was used to define parity. his threshold is
now controversial because many states still use this weight to
Prenata l Ca re
diferentiate a stillborn fetus from an abortus (Chap. 1 , p. 3) .
However, the survival of neonates with birthweights < 500 g
is no longer uncommon.
5. Multpara-a woman who has completed two or more preg­
nancies to 20 weeks' gestation or more. Parity is determined
by the number of pregnancies reaching 20 weeks. It is not
increased to a higher number if multiples are delivered in
a given pregnancy. Moreover, stillbirth does not lower this
number. In some locales, the obstetrical history is summa­
rized by a series of digits connected by dashes. hese refer
to the number of term infants, preterm infants, abortuses
younger than 20 weeks, and children currently alive. For
example, a woman who is para 2-1 -0-3 has had two term
deliveries, one preterm delivery, no abortuses, and has three
living children. Because these are nonconventional, it is
helpful to speciy the outcome of any pregnancy that did not
end normally.
N ormal Preg na ncy D u ration
The normal duration of pregnancy calculated from the irst day
of the last normal menstrual period is very close to 280 days or
40 weeks. In a study of 427, 5 8 1 singleton pregnancies from the
Swedish Birth Registry, Bergsj0 and coworkers ( 1 990) found
that the mean pregnancy duration was 2 8 1 days with a standard
deviation of 1 3 days. However, menstrual cycle length varies
among women and renders many of these calculations inac­
curate. This, combined with the frequent use of irst-trimester
sonography, has changed the method of determining an accu­
rate gestational age (Duryea, 20 1 5) .
h e American College o f Obstetricians and Gynecologists
(20 1 7e) , the American Institute of Ultrasound in Medicine,
and the Society for Maternal-Fetal Medicine have concluded
that irst-trimester ultrasound is the most accurate method to
establish or reairm gestational age. For pregnancies conceived
by assisted reproductive technology, embryo age or transfer
date is used to assign gestational age. If available, the gesta­
tional ages calculated from the last menstrual period and from
irst-trimester ultrasound are compared, and this estimated date
of delivery is recorded. his is discussed in further detail in
Chapter 7 (p. 1 24) and in Table 1 0- 1 (p. 1 83) .
A quick estimate of a pregnancy due date based on men­
strual data can be made as follows: add 7 days to the irst day of
the last period and subtract 3 months. For example, if the irst
day of the last menses was October 5, the due date is 1 0-0 5
minus 3 (months) plus 7 (days) = 7- 1 2, or July 1 2 of the
following year. his calculation is the Naegele rule (American
College of Obstetricians and Gynecologists, 20 1 7 e) .
Tri mesters
It has become customary to divide pregnancy into three equal
epochs or trimesters of approximately 3 calendar months. His­
torically, the irst trimester extends through completion of 1 4
weeks, the second through 2 8 weeks, and the third includes the
29th through 42nd weeks of pregnancy. Thus, there are three
periods of 1 4 weeks each. Certain major obstetrical problems
tend to cluster in each of these time periods. For example, most
spontaneous abortions take place during the irst trimester,
whereas most women with hypertensive disorders due to preg­
nancy are diagnosed during the third trimester.
In modern obstetrics, the clinical use of trimesters to
describe a speciic pregnancy is imprecise. For example , it is
inappropriate in cases of uterine hemorrhage to categorize the
problem temporally as "third-trimester bleeding. " Appropriate
management for the mother and her fetus will vary remark­
ably depending on whether bleeding begins early or late in the
th ird trimester (Chap. 4 1 , p. 757) . Because precise knowledge
of fetal age is imperative for ideal obstetrical management, the
clinically appropriate unit is weeks ofgestation complete. And
more recently, clinicians designate gestational age using com­
pleted weeks and days, for example, 3 3 4/7 weeks or 33 + 4, for
33 completed weeks and 4 days.
Previous a n d Cu rrent Hea lth Status
As elsewhere in medicine, history taking begins with queries
concerning medical or surgical disorders. Also, detailed infor­
mation regarding previous pregnancies is essential as many
obstetrical complications tend to recur in subsequent pregnan­
cies. The menstrual and contraceptive histories are also impor­
tant. Gestational or menstrual age is the number of weeks since
the onset of the last menstrual period in women with menstrual
cycles lasting 28 to 30 days. For those with irregular m enses,
sonography in early pregnancy will clariy gestational age. Last,
some methods of birth control favor ectopic implantation fol­
lowing method failure (Chap. 38, pp. 683 and 689) .
Psychosocial Screening. The American Academy of Pediatrics
and the American College of Obstetricians and Gynecologists
(20 1 7) defi n e psychosocial issues as nonbiomedical factors
that afect mental and physical well-being. Women should be
screened regardless of social status, education level, race, or eth­
nicity. Such screening should seek barriers to care, communica­
tion obstacles, nutritional status, unstable housing, desire for
pregnancy, safety concerns that include intimate-partner vio­
lence, depression, stress, and use of substances such as tob acco,
alcohol, and illicit drugs. his screening is performed on a regu­
lar basis, at least once per trimester, to identiy important issues
and reduce adverse pregnancy outcomes. Coker and colleagues
(20 1 2) compared pregnancy outcomes in women before and
after implementation of a universal psychosocial screening
program and found that screened women were less likely to
have preterm or low-birthweight newborns, as well as other
adverse outcomes. Speciic screens for depression are presented
in Chapter 61 (p. 1 1 74) .
Cigarette Smoking. Data on this practice have been included
on the birth certiicate since 1 9 89. The number of pregnant
women who smoke continues to decline. From 2000 to 2 0 1 0,
the prevalences were 1 2 to 1 3 percent (Tong, 20 1 3) . Based
on the Pregnancy Risk Assessment Monitoring System, these
women were more likely younger, had less education, and were
either Alaska Natives or American Indians (Centers for Disease
Control and Prevention, 20 1 3a) .
Numerous adverse outcomes have been linked to smoking
during pregnancy (U. S . D epartment of Health and H uman
S ervices, 2000) . Potential teratogenic efects are reviewed in
1 61
1 62
P reconcept i o n a l a n d P renatal Care
TABLE 9-2. Five A's of Smoking Cessation
A S K a bo ut s moking at the fi rst and s u bseq uent p renata l visi ts.
ADVI S E with clear, stro ng state me nts that expl a i n the risks of conti n ued smoking to the wom a n , fet u s, a n d newborn .
ASSESS the patient's wi l l i n g n ess to atte m pt cessation .
ASSIST with preg nancy-spec ific, self- h e l p smoking cessatio n mate r i a l s. Ofer a d i rect referra l to the sm oker's q u it l i ne
( 1 -800-Q U IT NOW) to p rovi d e o n g o i n g co u n se l i ng a n d s u pport.
ARRANGE to track smoking a b sti nence p rog ress at s u bseq uent vis its.
Ada pted from F io re, 2008.
Chapter 1 2 (p. 249) . Notable among these are greater rates of
miscarriage, stillbirth, low birthweight, and preterm delivery
(Man, 2006; Tong, 20 1 3) . here is also a twofold risk of
placenta previa, placental abruption, and premature mem­
brane rupture compared with nonsmokers. hus, the U.S.
Preventive Services Task Force recommends that clinicians
ofer counseling and efective intervention options to preg­
nant smokers at the irst and subsequent prenatal visits (Siu,
2 0 1 5 ) . Although beneits are greatest if smoking ceases early
in pregnancy or preferably preconceptionally, quitting at any
stage of pregnancy can improve perinatal outcomes (Fiore,
2008 ) .
Person-to-person psychosocial interventions are signiicantly
more successful in achieving smoking abstinence in pregnancy
than is simply advising the woman to quit (Fiore, 2008) . One
example is a brief counseling session covering the "5As" of
smoking cessation (Table 9-2) . This approach can be accom­
plished in 1 5 minutes or less and is efective when initiated by
health-care providers (American College of Obstetricians and
Gynecologists, 20 1 7i) .
Behavioral interventions and nicotine replacement products
are successful in reducing smoking rates (Patnode, 20 1 5) . hat
said, nicotine replacement has not been suiciently evaluated to
determine its efectiveness and safety in pregnancy. Trials evalu­
ating such therapy have yielded confl i cting evidence (Coleman,
20 1 5 ; Pollak, 2007; Spindel, 20 1 6) . Two recent randomized
trials also produced nonconclusive results. In the Smoking and
Nicotine in Pregnancy (SNAP) trial, Cooper and associates
(20 1 4) reported a temporary cessation of smoking that may
have been associated with improved infant development. In the
Study of Nicotine Patch in Pregnancy (SNIPP) trial, Berlin and
coworkers (20 1 4) found no diferences in smoking cessation
rates or birthweights.
Because of limited available evidence to support pharma­
cotherapy for smoking cessation in pregnancy, the American
College of Obstetricians and Gynecologists (20 1 7i) has recom­
mended that if nicotine replacement therapy is used, it should
be done with close supervision and after careful consideration
of the risks of smoking versus nicotine replacement.
Alcohol. Ethyl acohol or ethanol is a potent teratogen that causes
a etal syndrome characterized by growth restriction, acial abnor­
malities, and central nervous system dyunction. s discussed in
Chapter 1 2 (p. 239), women who are pregnant or consider­
ing pregnancy should abstain from using any alcoholic bever­
ages. The CDC analyzed data from the Behavioral isk Factor
Surveillance System from 20 1 1 to 20 1 3 and estimated that
1 0 percent of pregnant women used alcohol. It is estimated that
3.3 million women are at risk for such exposure (Green, 20 1 6) .
h e American College o f Obstetricians and Gynecologists
(20 1 6b) in collaboration with the CDC has developed the Fetal
Acohol Spectrum Disorders (FASD) Prevention Program, which
provides resources for providers and is available at: http://www.
acog.org/ alcohol.
Il licit Drugs. It is estimated that 1 0 percent of fetuses are exposed
to one or more illicit drugs. Agents may include heroin and other
opiates, cocaine, amphetamines, barbiturates, and marijuana
(American Academy of Pediatrics, 20 1 7; merican College of
Obstetricians and Gynecologists, 20 1 5a, 20 1 7d) . As discussed in
Chapter 12 (p. 247), chronic use of most of these in large quan­
tities is harmful to the fetus (Metz, 20 1 5) . Well-documented
sequelae include fetal-growth restriction, low birthweight, and
drug withdrawal soon ater birth. Adverse efects of marijuana
are less convincing. Women who use such drugs frequently do
not seek prenatal care, which in itself is associated with risks for
preterm and low-birthweight newborns (EI-Mohandes, 2003;
Eriksen, 20 1 6) .
For women who abuse heroin, methadone maintenance can
be initiated within a registered methadone treatment program
to reduce complications of illicit opioid use and narcotic with­
drawal, to encourage prenatal care, and to avoid drug culture
risks (American College of Obstetricians and Gynecologists,
20 1 7£) . Available programs can be found through the treatment
locator of the Substance Abuse and Mental Health Services
Administration at ww.samhsa.gov. Methadone dosages usually
are initiated at 1 0 to 30 mg daily and titrated as needed. In some
women, careful methadone taper may be an appropriate option
(Stewart, 20 1 3) . Although less commonly used, buprenorphine
alone or in combination with naloxone may also be ofered and
managed by physicians with specific credentialing.
I ntimate-Partner Violence. his term refers to a pattern of
assault and coercive behavior that may include physical injury,
psychological abuse, sexual assault, progressive isolation, stalk­
ing, deprivation, intimidation, and reproductive coercion
(American College of Obstetricians and Gynecologists, 20 1 2) .
Such violence has been recognized as a major public health
problem. Unfortunately, most abused women continue to be
victimized during pregnancy. With the possible exception of
preeclampsia, domestic violence is more prevalent than any
major medical condition detectable through routine prenatal
P renata l Ca re
screening (American Academy of Pediatrics and the Ameri­
can College of Obstetricians and Gynecologists, 20 1 7) . The
prevalence during pregnancy is estimated to range between 4
and 8 percent. Intimate-partner violence is associated with an
increased risk of several adverse perinatal outcomes including
preterm delivery, fetal-growth restriction, and perinatal death
(Chap. 47, p. 925).
The American College of Obstetricians and Gynecologists
(20 1 2) has provided methods for domestic violence screen­
ing and recommends their use at the irst prenatal visit, then
again at least once per trimester, and again at the postpartum
visit. Such screening should be done privately and away from
family members and friends. Patient self-administered or com­
puterized screenings appear to be as efective for disclosure
as clinician-directed interviews (Ahmad, 2009; Chen, 2007) .
Physicians should be familiar with state laws that may require
reporting of intimate-partner violence. Coordination with
social services can be invaluable in these cases. The National
Domestic Violence Hotline ( l -800-799-SAFE [7233] ) is a
nonprofit telephone referral service that provides individualized
information regarding city-speciic shelter locations, counseling
resources, and legal advocacy.
• Clinical Evaluation
A thorough, general physical examination should be com­
pleted at the initial prenatal encounter. Pelvic examination is
performed as part of this evaluation. he cervix is visualized
employing a speculum lubricated with warm water or water­
based lubricant gel. Bluish-red passive hyperemia of the cer­
vix is characteristic, but not of itself diagnostic, of pregnancy.
Dilated, occluded cervical glands bulging beneath the ectocer­
vical mucosa-nabothian cysts-may be prominent. he cervix
is not normally dilated except at the external os. To identiy
cytological abnormalities, a Pap test is performed according to
current guidelines noted in Chapter 63 (p. 1 1 93). Specimens
for identiication of Chlamydia trachomatis and Neisseria gonor­
rhoeae are also obtained when indicated.
Bimanual examination is completed by palpation, with spe­
cial attention given to the consistency, length, and dilatation
of the cervix; to uterine and adnexal size; to the bony pelvic
architecture; and to any vaginal or perineal anomalies. Later
in pregnancy, fetal presentation often can also be determined.
Lesions of the cevix, vagina, or vulva are further evaluated as
needed by colposcopy, biopsy, culture, or dark-field examina­
tion. The perianal region is visualized, and digital rectal exami­
nation performed as required for complaints of rectal pain,
bleeding, or mass.
Gestationa l Age Assessment
Precise knowledge of gestational age is one of the most impor­
tant aspects of prenatal care because several pregnancy compli­
cations may develop for which optimal treatment will depend
on fetal age. As discussed earlier and in Chapter 7 (p. 1 24) ,
irst-trimester sonographic assessment is best correlated with
menstrual history. That said, gestational age can also be esti­
mated with considerable precision by carefully performed clini­
cal uterine size examination that is coupled with knowledge of
the last menses. Uterine size similar to a small orange roughly
correlates with a 6-week gestation; a large orange, with an
8-week pregnancy; and a grapefruit, with one at 12 weeks
(Margulies, 200 1 ) .
• Laboratory Tests
Recommended routine tests at the first prenatal encounter
are listed in Table 9- 1 . Initial blood tests include a complete
blood count, a determination of blood type with h status,
and an antibody screen. The Institute of Medicine recommends
universal human immunodeiciency virus (HIV) testing, with
patient notiication and right of refusal, as a routine part of pre­
natal care. The CDC (Branson, 2006) as well as the American
Academy of Pediatrics and the American College of Obstetri­
cians and Gynecologists (20 1 6f, 20 1 7) continue to suppo rt this
practice. If a woman declines testing, this is recorded in the
prenatal record. All pregnant women are also screened for hepa­
titis B virus infection, syphilis, and immunity to rubella at the
initial visit. Based on their prospective investigation of 1 000
women, Murray and coworkers (2002) concluded that in the
absence of hypertension, routine urinalysis beyond the irst pre­
natal visit was not necessary. A urine culture is recommended
by most because treating bacteruria signiicantly reduces the
likelihood of developing symptomatic urinary tract infections
in pregnancy (Chap. 53, p. 1 026) .
Cervica l I nfectio n s
Chlamydia trachomatis is isolated from the cervix in 2 to 13 per­
cent of pregnant women. he American Academy of Pediatrics
and the American College of Obstetricians and Gynecologists
(20 1 7) recommend that all women be screened for chlamydia
during the irst prenatal visit, with additional third-trimester
testing for those at increased risk. Risk factors include unmarried
status, recent change in sexual partner or multiple concurrent
partners, age younger than 25 years, inner-city residence, history
or presence of other sexually transmitted diseases, and little or
no prenatal care. For those testing positive, treatment described
in Chapter 65 (p. 1 240) is followed by a second testing-a test
ofcure-3 to 4 weeks after treatment completion.
Neisseria gonorrhoeae typically causes lower genital tract
infection in pregnancy. It also may cause septic arthritis ( Bleich,
20 1 2) . Risk factors for gonorrhea are similar to those for chla­
mydial infection. The American Academy of Pediatrics and the
American College of Obstetricians and Gynecologists (20 1 7)
recommend that pregnant women with risk factors or those liv­
ing in an area of high N gonorrhoeae prevalence be screened at
the initial prenatal visit and again in the third trimester. Treat­
ment is given for gonorrhea and simultaneously for possible
coexisting chlamydial infection (Chap. 65, p. 1 240) . Test of
cure is also recommended following treatment.
• Pregnancy Risk Assessment
Many factors can adversely afect maternal and fetal well-being.
Some are evident at conception, but many become apparent
during the course of pregnancy. The designation of "high-risk
pregnancy" is overly vague for an individual woman and prob­
ably is best avoided if a more specific diagnosis can be assigned.
1 63
1 64
P reco n ceptiona l a n d P re natal Care
TABLE 9-3. Conditions for Which Materna l-Feta l Med icine Consu ltation May Be Beneficia l
Medical History and Cond itions
Card iac d isease-moderate to severe d i so rd ers
D i a betes m e l l itus with evid en ce of e n d-org a n da mage or u n contro i led hyperg lycemia
Fa m i l y o r perso n a l h i story of g e n etic a b n o rm a l ities
H em og lo b i nopathy
C h ro n i c hyperten s i o n if u ncontro l l ed or associated with ren a l r cardiac d i sease
Renal i ns ufici ency if a ssoci ated with sig n ificant prote i n u ria ( ::500 m g/24 h o u r), seru m
c reat i n i ne ::1 .5 m g/d L, or hyperten s i o n
P u l m o n a ry d i sease if seve re restrictive o r obstructive, i n c l u d i n g severe asthma
H u ma n i m m u n od eficiency virus i nfection
P rior p u l m o n a ry e m bo l u s or d ee p-ve i n t h rom bos is
Severe system ic d i sea se, i nc l u d i n g a utoi m m u n e con d itions
Ba riatric s u rg e ry
E p i lepsy if poorly contro l led or req u i res more t h a n one a nticonvu l s a nt
Cancer, espec i a l l y if t reatm e n t is i n d icated i n preg n a n cy
Obstetrical History and Conditions
CDE (Rh) o r other b lood g r o u p a l l oi m m u n ization (exc l u d i ng ABO, Lewis)
P rior or cu rrent feta l struct u ra l o r c h ro m osoma l a bn o rm a l ity
Des i re or need for prenata l d i a g n o s i s or feta l thera py
Perico nceptional expo s u re to known teratoge n s
I nfection w i t h or expo s u re to o rga n is m s that c a u s e congen ita l i nfection
H ig h e r-ord e r m u l tifeta l g estation
Severe d i sord e rs of a m n io n ic fl u i d vo l u me
Some common risk factors for which consultation is recom­
mended by the American Academy of Pediatrics and the Amer­
ican College of Obstetricians and Gynecologists (20 1 7) are
shown in Table 9-3 . Some conditions may require the involve­
ment of a maternal-fetal medicine subspecialist, geneticist,
pediatrician, anesthesiologist, or other medical specialist in the
evaluation, counseling, and care of the woman and her fetus.
SU BSEQUENT PRENATAL VISITS
hese are traditionally scheduled at 4-week intervals until 28
weeks, then every 2 weeks until 36 weeks, and weekly thereaf­
ter. Women with complicated pregnancies-for example, with
twins or diabetes-often require return visits at 1 - to 2-week
intervals (Luke, 2003; Power, 20 1 3) . In 1 986, the Department
of Health and Human Services convened an expert panel to
review the content of prenatal care. his report was subsequently
reevaluated and revised in 2005 (Gregory, 2006) . he panel
recommended, among other things, early and continuing risk
assessment that is patient speciic. It also endorsed lexibility in
clinical visit spacing; health promotion and education, includ­
ing preconceptional care; medical and psychosocial interven­
tions; standardized documentation; and expanded prenatal care
objectives-to include family health up to 1 year after birth.
he World Health Organization conducted a multicenter
randomized trial with almost 25 ,000 women comparing rou­
tine prenatal care with an experimental model designed to
minimize visits (Villar, 200 1 ) . In the new model, women were
seen once in the irst trimester and screened for certain risks.
hose without anticipated complications-80 percent of those
screened-were seen again at 26, 32, and 38 weeks. Compared
with routine prenatal care, which required a median of eight
visits, the new model required a median of only ive. No dis­
advantages were attributed to the regimen with fewer visits,
and these indings were consistent with other randomized trials
(Clement, 1 999; McDuie, 1 996) .
• Prenatal Surveillance
At each return visit, the well-being of mother and fetus are
assessed (see Table 9- 1 ) . Fetal heart rate, growth, and activity
and amnionic fluid volume are evaluated. Maternal blood pres­
sure and weight and their extent of change are examined. Symp­
toms such as headache, altered vision, abdominal pain, nausea
and vomiting, bleeding, vaginal luid leakage, and dysuria are
sought. Mter 20 weeks' gestation, uterine examination mea­
sures size from the symphysis to the fundus. In late pregnancy,
vaginal examination often provides valuable information that
includes conirmation of the presenting part and its station,
clinical estimation of pelvic capacity and configuration, amni­
onic luid volume adequacy, and cervical consistency, eface­
ment, and dilatation (Chap. 22, p. 435) .
F u n d a l H e i g ht
Between 20 and 34 weeks' gestation, the height of the uter­
ine fundus measured in centimeters correlates closely with
gestational age in weeks Gimenez, 1 983) . his measurement is
used to monitor fetal growth and amnionic fluid volume. It is
measured along the abdominal wall from the top of the sym­
physis pubis to the top of the fundus. Importantly, the bladder
P renata l Ca re
must be emptied before fundal measurement (Worthen, 1 980) .
Obesity or the presence of uterine masses such as leiomyomas
may also limit fundal height accuracy. Moreover, using fundal
height alone, fetal-growth restriction may be undiagnosed in
up to a third of cases (American College of Obstetricians and
Gynecologists, 20 1 5 b; Haragan, 20 1 5) .
(American College of Obstetricians and Gynecologists, 20 1 6) .
Similarly, women who engage i n behaviors that place them at
high risk for hepatitis B virus infection are retested at the time
of hospitalization for delivery. Women who are D (h) nega­
tive and are unsensitized should have an antibody screening
test repeated at 28 to 29 weeks, and anti-D immunoglobulin is
given if they remain unsensitized (Chap. 1 5 , p. 305).
Feta l Heart Sou n d s
Instruments incorporating Doppler ultrasound are often used
to easily detect fetal heart action, and in the absence of maternal
obesity, heart sounds are almost always detectable by 1 0 weeks
with such instruments (Chap. 1 0, p. 2 1 3) . he fetal heart rate
ranges from 1 1 0 to 1 60 beats per minute and is typically heard
as a double sound. Using a standard nonampliied stethoscope,
the fetal heart is audible by 20 weeks in 80 percent of women,
and by 22 weeks, heart sounds are expected to be heard in
all (Herbert, 1 987) . Because the fetus moves freely in amni­
onic fl u id, the site on the maternal abdomen where fetal heart
sounds can be heard best will vary.
Additionally, with ultrasonic auscultation, one may hear
the unic soule, which is a sharp, whistling sound that is syn­
chronous with the fetal pulse. It is caused by the rush of blood
through the umbilical arteries and may not be heard consistently.
In contrast, the uterine soule is a soft, blowing sound that is
synchronous with the maternal pulse. It is produced by the pas­
sage of blood through the dilated uterine vessels and is heard
most distinctly near the lower portion of the uterus.
Sonog ra phy
Sonography provides invaluable information regarding fetal
anatomy, growth, and well-being, and most women in the
United States have at least one prenatal sonographic exami­
nation during pregnancy (American College of Obstetricians
and Gynecologists, 20 1 6h) . Continuing trends suggest that
the number of these examinations performed per pregnancy
is increasing. Siddique and associates (2009) reported that the
average number rose from 1 . 5 in 1 995 through 1 997 to 2.7
almost 10 years later. his trend was noted in both high- and
low-risk pregnancies. he actual clinical utility of this increased
use in pregnancy has not been demonstrated, and it is unclear
that the cost-benefi t ratio is justified (Washington State Health
Care Authority, 20 1 0) . The American College of Obstetricians
and Gynecologists (20 1 6h) has concluded that sonography
should be performed only when there is a valid medical indica­
tion and under the lowest possible ultrasound exposure setting.
The College further states that a physician is not obligated to
perform sonography without a specific indication in a low-risk
patient, but that if she requests sonographic screening, it is rea­
sonable to honor her request.
• Subsequent Laboratory Tests
If initial results were normal, most tests need not be repeated.
Hematocrit or hemoglobin determination, along with serology
for syphilis if it is prevalent in the population, is repeated at 28
to 32 weeks (Hollier, 2003; Kiss, 2004) . For women at increased
risk for HIV acquisition during pregnancy, repeat testing is rec­
ommended in the third trimester, preferably before 36 weeks
Gro u p B Streptococca l I nfection
he CDC (20 1 0b) recommends that vaginal and rectal group B
streptococcal (GBS) cultures be obtained in all women between
35 and 37 weeks' gestation, and the American College of Obste­
tricians and Gynecologists (20 1 6g) has endorsed this recom­
mendation. Intrapartum antimicrobial prophylaxis is provided
to those whose culture results are positive. Women with GBS
bacteriuria or a previous infant with invasive disease are given
empirical intrapartum prophylaxis. Trials are in progress to test
an investigational vaccine (Donders, 20 1 6; Schrag, 20 1 6) . hese
infections are described further in Chapter 64 (p. 1 220) .
Gestation a l Dia betes
All pregnant women are screened for gestational diabetes mel­
litus, whether by history, clinical factors, or routine laboratory
testing. Although laboratory testing between 24 and 28 weeks'
gestation is the most sensitive approach, there may be pregnant
women at low risk who are less likely to beneit from testing
(American College of Obstetricians and Gynecologists, 2 0 1 7c) .
Gestational diabetes is discussed in Chapter 57 (p. 1 1 07) .
N e u ra l -Tu be Defect a n d G e n etic Scree n i n g
Serum screening for neural-tube defects i s ofered at 1 5 to
20 weeks. Fetal aneuploidy screening may be performed at 1 1
to 1 4 weeks' gestation and/or at 1 5 to 20 weeks, depending on
the protocol selected (Rink, 20 1 6) . Additionally, screening for
certain genetic abnormalities is ofered to women at increased
risk based on family history, ethnic or racial background, or
age (American College of Obstetricians and Gynecologists,
20 1 7h) . These are discussed in greater detail in Chapter 1 4
(p. 277) . Some examples include testing for Tay-Sachs disease
for persons of Eastern European Jewish or French Canadian
ancestry; � -thalassemia for those of Mediterranean, Southeast
Asian, Indian, Pakistani, or Mrican ancestry; a-thalassemia for
individuals of Southeast Asian or Mrican ancestry; sickle-cell
anemia for people of African, Mediterranean, Middle Eastern,
Caribbean, Latin American, or Indian descent; and trisomy 2 1
for those with advanced maternal age.
N UTRITIONAL COU NSELING
• Weight Gain Recommendations
In 2009, the Institute of Medicine and National Research
Council revised guidelines for weight gain in pregnancy and
continued to stratiy suggested weight gain ranges based on
prepregnancy body mass index (BMI) (Table 9-4) . The new
guidelines included a specific, relatively narrow range of recom­
mended weight gains for obese women. Also, the same recom­
mendations apply to adolescents, short women, and women of
1 65
1 66
P recon cepti o n a l a n d P renata l Care
TABLE 9-4. Reco m m endations for Total a n d Rate of
We i g ht G a i n During Preg na ncy
Category (BMI)
U nd e rwe i g h t
« 1 8.5)
Normal wei g h t
( 1 8.5-24.9)
Ove rweig ht
(25 .0-29.9)
Obese (::30.0)
Total Weight
Gai n Range
( l b)a
Weight Gain i n 2nd
and 3rd Tri mesters
Mean in I b/wk (range)
28-40
1 ( 1 - 1 .3)
25-35
1 (0.8- 1 )
1 5-25
0.6 (0.5-0.7)
1 1 -20
0.5 (0.4-0.6)
a E m p i rica l reco m me n d at i o n s for wei g h t g a i n i n twi n
preg n a ncies i n cl ude: norma l BMI, 3 7-54 I b; ove rwe i g ht
wo men, 3 1 -5 0 I b; a n d o bese wom en, 25-42 l b.
B M I body mass i n d ex.
Mod ifi ed from t h e I n st i tute of Med i c i n e a n d National
Research Cou n c i l , 2009.
=
all racial and ethnic groups. The American College of Obstetri­
cians and Gynecologists (20 1 6i) has endorsed these measures.
When the Institute of Medicine guidelines were formulated,
concern focused on low-birthweight newborns, however, cur­
rent emphasis is directed to the obesity epidemic (Catalano,
2007) . This explains renewed interest in lower weight gains dur­
ing pregnancy. Obesity is associated with significantly greater
risks for gestational hypertension, preeclampsia, gestational dia­
betes, macrosomia, cesarean delivery, and other complications
(Chap. 48, p. 939) . he risk appears "dose related" to prenatal
weight gain. In a population-based cohort of more than 1 20,000
obese pregnant women, those who gained <15 lb had the low­
est rates of preeclampsia, large-for-gestational age neonates, and
cesarean delivery (Kiel, 2007) . Among 1 00,000 women with
normal prepregnancy BMI, DeVader and colleagues (2007)
found that those who gained <25 Ib during pregnancy had
a lower risk for preeclampsia, failed induction, cephalopelvic
disproportion, cesarean delivery, and large-for-gestational age
neonates. his cohort, however, had an increased risk for small­
for-gestational age newborns. Lifestyle intervention during preg­
nancy can result in less weight gain (Sagedal, 20 1 7) .
There i s irrefutable evidence that maternal weight gain dur­
ing pregnancy inluences birthweight. Martin and cowork­
ers (2009) studied this using birth certificate data for 2006.
Approximately 60 percent of women gained 26 Ib or more dur­
ing pregnancy, and maternal weight gain positively correlated
with birthweight. Nloreover, women with the greatest risk1 4 percent-for delivering a newborn weighing < 2500 g were
those with weight gain < 1 6 lb. Nearly 20 percent of births to
women with such low weight gains were preterm.
• Severe Undernutrition
Meaningful studies of nutrition in human pregnancy are
exceedingly diicult to design because experimental dietary defi­
ciency is not ethical. In those instances in which severe nutri­
tional deiciencies have been induced as a consequence of social,
economic, or political disaster, coincidental events have oten
created many variables, the efects of which are not amenable to
quantiication. Some past experiences suggest, however, that in
otherwise healthy women, a state of near starvation is required
to establish clear diferences in pregnancy outcome.
During the severe European winter of 1 944 to 1 945,
nutritional deprivation of known intensity prevailed in a well­
circumscribed area of The Netherlands occupied by the German
military (Kyle, 2006) . At the lowest point during this Dutch
Hunger Winter, rations reached 450 kcal/d, with generalized
rather than selective malnutrition. Smith ( 1 947) analyzed the out­
comes of pregnancies that were in progress during this 6-month
famine. Median neonatal birthweights declined approximately
250 g and rose again ater food became available. This indicated
that birthweight can be inluenced significantly by starvation
during later pregnancy. he perinatal mortality rate, however,
was not altered. Moreover, the incidence of fetal malformations
or preeclampsia did not rise signiicantly. Parenthetically, weight
loss in obese women during pregnancy is also associated with an
increased risk for low-birthweight neonates (Cox Bauer, 20 1 6) .
Evidence o f impaired brain development has been obtained
in some animal fetuses whose mothers had been subjected to
intense dietary deprivation. Subsequent intellectual develop­
ment was studied by Stein and associates ( 1 972) in young male
adults whose mothers had been starved during pregnancy in
the aforementioned Hunger Winter. The comprehensive study
was made possible because all males at age 1 9 underwent com­
pulsory examination for military service. It was concluded that
severe dietary deprivation during pregnancy caused no detect­
able efects on subsequent mental performance.
Several studies of the long-term consequences to this cohort
of children born to nutritionally deprived women have been
performed and have been reviewed by Kyle and Pichard (2006) .
Progeny deprived in mid to late pregnancy were lighter, shorter,
and thinner at birth, and they had a higher incidences of sub­
sequent hypertension, reactive airway disease, dyslipidemia,
diminished glucose tolerance, and coronary artery disease. Early
pregnancy deprivation was associated with greater obesity rates
in adult women but not men. Early starvation was also linked
to higher rates of central nervous system anomalies, schizophre­
nia, and schizophrenia-spectrum personality disorders.
hese observations and others have led to the concept of
etal programming by which adult morbidity and mortality are
related to fetal health. Known widely as the Barker hypothesis,
as promulgated by Barker and colleagues ( 1 989), this concept
is discussed in Chapter 44 (p. 848).
• Weight Retention ater Pregnancy
Not all the weight gained during pregnancy is lost during and
immediately after delivery. Schauberger and coworkers ( 1 992)
studied prenatal and postpartum weights in 795 women.
Their average weight gain was 28.6 Ib or 1 2.9 kg. As shown
in Figure 9-4, most maternal weight loss was at delivery­
approximately 1 2 lb or 5 .4 kg-and in the ensuing 2 weeks­
approximately 9 Ib or 4 kg. An additional 5 . 5 lb or 2.5 kg was
lost between 2 weeks and 6 months postpartum. Thus, average
retained pregnancy weight was 2 . 1 Ib or 1 kg. Excessive weight
gain is manifest by accrual of fat and may be partially retained as
P renata l Care
18
TABLE 9-5. Recommended Da i ly D i etary Al lowances for
P regnant and Lactat i n g Women
16
) 14
�
12
)
Q
E
)
10
'w
�
>
8
6
4
2
790
0
n
=
2
4
6
8
6 1 8 31 3 554 222
409
1 0 1 2 1 4 1 6 1 8 20 22 24 26
483
Time in weeks
FIGURE 9-4 C u m u lative wei g ht l oss from last a ntepa rtum visit
to 6 months postpa rt u m . *Sig n ificantly d ifferent from 2-week
weig ht loss; **S i g n ifica ntly d ifferent from 6-week weight loss.
(Redrawn from Schau berg er CW, Rooney BL, Brimer LM: Factors
that i nfl uence wei g ht loss in the puerperi u m . Obstet Gynecol
79:424, 1 992.)
long-term fat (Berggren, 20 1 6; Widen, 20 1 5) . Overall, the more
weight that was gained during pregnancy, the more that was lost
postpartum. Interestingly, there is no relationship between pre­
pregnancy BMI or prenatal weight gain and weight retention.
• Dietary Reference Intakes-Recommended
Allowances
Periodically, the Institute of Medicine (2006, 20 1 1 ) publishes
recommended dietary allowances, including those for pregnant
or lactating women. The latest recommendations are summa­
rized in Table 9-5. Certain prenatal vitamin-mineral supple­
ments may lead to intakes well in excess of the recommended
allowances. Moreover, the use of excessive supplements, which
often are self-prescribed, has led to concern regarding nutrient
toxicities during pregnancy. Those with potentialy toxic fects
include iron, zinc, selenium, and vitamins A, B6, C, and D.
• Calories
As shown in Figure 9-5, pregnancy requires an additional
80,000 kcal, mostly during the last 20 weeks. To meet this
demand, a caloric increase of 1 00 to 300 kcal/d is recom­
mended during pregnancy (American Academy of Pediatrics
and the American College of Obstetricians and Gynecologists,
20 1 7) . This greater intake, however, should not be divided
equally during the course of pregnancy. The Institute of Medi­
cine (2006) recommends adding 0, 340, and 452 kcal/d to the
estimated nonpregnant energy requirements in the irst, second,
and third trimesters, respectively. he addition of 1 000 kcal/d
or more results in fat accrual Qebeile, 20 1 5) .
Calories are necessary for energy. Whenever caloric intake is
inadequate, protein is metabolized rather than being spared for
its vital role in fetal growth and development. Total physiologi­
cal requirements during pregnancy are not necessarily the sum
of ordinary nonpregnant requirements plus those speciic to
pregnancy. For example, the additional energy required during
Pregnant
Lactating
Fat-Soluble Vitam ins
Vita m i n A
Vita m i n Da
Vita m i n E
Vita m i n Ka
77O l1g
1 5 11g
1 5 mg
9O 1g
1 300 1g
1 5 11g
1 9 mg
90 1g
Water- Soluble Vita m i ns
Vita m i n C
Th ia m i n e
Ri boflavi n
N ia c i n
Vita m i n B6
Fol ate
Vita m i n B 1 2
85 mg
1 .4 mg
1 .4 mg
1 8 mg
1 .9 mg
6OO 1g
2.6 1g
1 20 mg
1 .4 mg
1 .6 mg
1 7 mg
2 mg
5OO 1g
2.8 1g
1 000 mg
1 .5 9
4.7 9
27 mg
1 1 mg
220 -1g
6O 1g
1 000 mg
1 .5 9
5.1 9
9 mg
1 2 mg
29O -1g
7O l1g
71 9
1 75 9
28 9
71 9
21 0 9
29 9
M i nerals
Ca l c i u ma
Sod i u ma
Potassi u ma
I ro n
Z i nc
I od i n e
Selen i u m
Other
P rote i n
Ca rbohyd rate
F i bera
aReco m mendations mea s u red a s adeq u ate i n ta ke.
F ro m the I n stitute of Medici n e, 2006, 20 1 1 .
pregnancy may be compensated in whole or in part by reduced
physical activity (Hytten, 1 99 1 ) .
• Protein
Protein requirements rise to meet the demands for growth and
remodeling of the fetus, placenta, uterus, and breasts, and for
80 ,000
70,000
60 ,000
B
Maintenance
50, 000
40, 000
�
30, 000
)
20,000
1 0 ,000
0
Fat
...:;=,Protein
10
20
30
Weeks of pregnancy
40
FIGURE 9-5 Cu m ulative kilocalories requ i red for pregnancy. (Redrawn
from Cha m berlain G, Broug hton-Pipki n F (eds): Clinical P hysiology i n
Obstetrics, 3 rd ed. Oxford, Blackwell Science, 1 998.)
1 67
1 68
P reconceptional a n d P re nata l Ca re
increased maternal blood volume (Chap. 4, p. 5 5) . During the
second half of pregnancy, approximately 1 000 g of protein are
deposited, amounting to 5 to 6 g/d (Hytten, 1 97 1 ) . To accom­
plish this, protein intake that approximates 1 g/kg/d is recom­
mended (see Table 9-5). Data suggest this should be doubled in
late gestation (Stephens, 20 1 5) . Most amino-acid levels in mater­
nal plasma fall markedly, including ornithine, glycine, taurine,
and proline (Hytten, 1 99 1 ) . Exceptions during pregnancy are
glutamic acid and alanine, the concentrations of which rise.
Preferably, most protein is supplied from animal sources,
such as meat, milk, eggs, cheese, poultry, and fish. hese fur­
nish amino acids in optimal combinations. Milk and dairy
products are considered nearly ideal sources of nutrients, espe­
cially protein and calcium, for pregnant or lactating women.
Ingestion of specific ish and potential methylmercury toxicity
are discussed on page 1 70.
• Minerals
The intakes recommended by the Institute of Medicine (2006)
for various minerals are listed in Table 9-5. With the exception
of iron and iodine, practically all diets that supply suicient
calories for appropriate weight gain will contain enough miner­
als to prevent deiciency.
Iron requirements are greatly increased during pregnancy,
and reasons for this are discussed in Chapter 4 (p. 58). Of the
approximately 300 mg of iron transferred to the fetus and pla­
centa and the 500 mg incorporated into the expanding mater­
nal hemoglobin mass, nearly all is used after midpregnancy.
During that time, iron requirements imposed by pregnancy
and maternal excretion total approximately 7 mg/ d (Pritchard,
1 970) . Few women have suicient iron stores or dietary intake
to supply this amount. Thus, the American Academy of Pedi­
atrics and the American College of Obstetricians and Gyne­
cologists (20 1 7) endorse the recommendation by the National
Academy of Sciences that at least 27 mg of elemental iron be
supplemented daily to pregnant women. his amount is con­
tained in most prenatal vitamins.
Scott and coworkers ( 1 970) established that as little as
30 mg of elemental iron, supplied as ferrous gluconate, sulfate,
or fumarate and taken daily throughout the latter half of preg­
nancy, provides suicient iron to meet pregnancy requirements
and protect preexisting iron stores. his amount will also pro­
vide for iron requirements of lactation. he pregnant woman
may benefi t from 60 to 1 00 mg of elemental iron per day if
she is large, has a multifetal gestation, begins supplementation
late in pregnancy, takes iron irregularly, or has a somewhat
depressed hemoglobin level. he woman who is overtly ane­
mic from iron deficiency responds well to oral supplementation
with iron salts. In response, serum ferritin levels rise more than
the hemoglobin concentration (Daru, 20 1 6) .
Iodine is also needed, and the recommended iodine allow­
ance is 220 Lg/d (see Table 9-5 ) . The use of iodized salt and
bread products is recommended during pregnancy to ofset the
increased fetal requirements and maternal renal losses of iodine.
Despite this, iodine intake has declined substantially in the past
1 5 years, and in some areas it is probably inadequate (Casey,
20 1 7) . Severe maternal iodine deficiency predisposes ofspring to
endemic cretinism, which is characterized by multiple severe neu­
rological defects. In parts of China and Africa where this condi­
tion is common, iodide supplementation very early in pregnancy
prevents some cretinism cases (Cao, 1 994) . To obviate this, many
prenatal supplements now contain various quantities of iodine.
Cacium is retained by the pregnant woman during gestation
and approximates 30 g. Most of this is deposited in the fetus late
in pregnancy (Pitkin, 1 985). his amount of calcium represents
only approximately 2.5 percent of total maternal calcium, most
of which is in bone and can readily be mobilized for fetal growth.
s another potential use, routine calcium supplementation to pre­
vent preeclampsia has not proved efective (Chap. 40, p. 727) .
Zinc deficiency if severe may lead to poor appetite, subopti­
mal growth, and impaired wound healing. During pregnancy,
the recommended daily intake approximates 1 2 mg. But, the
safe level of zinc supplementation for pregnant women has not
been clearly established. Vegetarians have lower zinc intakes
(Foster, 20 1 5) . he bulk of studies support zinc supplementa­
tion only in zinc-deficient women in poor-resource countries
(Nossier, 20 1 5 ; Ota, 20 1 5) .
Manesium deficiency as a consequence o f pregnancy has not
been recognized. Undoubtedly, during prolonged illness with
no magnesium intake, the plasma level might become critically
low, as it would in the absence of pregnancy. We have observed
magnesium deiciency during pregnancies in some with previous
intestinal bypass surgery. As a preventive agent, Sibai and cowork­
ers ( 1 989) randomly assigned 400 normotensive primigravid
women to 365-mg elemental magnesium supplementation or
placebo tablets from 1 3 to 24 weeks' gestation. Supplementation
did not improve any measures of pregnancy outcome.
Trace metals include copper, selenium, chromium, and
manganese, which all have important roles in certain enzyme
functions. In general, most are provided by an average diet.
Selenium deficiency is manifested by a frequently fatal cardio­
myopathy in young children and reproductive-aged women.
Conversely, selenium toxicity resulting from oversupplementa­
tion also has been observed. Selenium supplementation is not
needed in American women.
Potassium concentrations in maternal plasma decline by
approximately 0 . 5 mEq/L by midpregnancy (Brown, 1 986) .
Potassium deficiency develops in the same circumstances as in
nonpregnant individuals-a common example is hyperemesis
gravidarum.
Fluoride metabolism is not altered appreciably during preg­
nancy (Maheshwari, 1 9 83) . Horowitz and Heifetz ( 1 967)
concluded that no additional ofspring beneits accrued from
maternal ingestion of luoridated water if the newborn ingested
such water from birth. Sa Roriz Fonteles and associates (2005)
studied microdrill biopsies of deciduous teeth and concluded
that antenatal luoride provided no additional fluoride uptake
compared with postnatal fluoride alone. Finally, supplemental
luoride ingested by lactating women does not raise the luoride
concentration in breast milk (Ekstrand, 1 9 8 1 ) .
• Vitamins
he increased requirements for most vitamins during preg­
nancy shown in Table 9-5 usually are supplied by any general
P re nata l C a re
diet that provides adequate calories and protein. he excep­
tion is folic acid during times of unusual requirements, such
as pregnancy complicated by protracted vomiting, hemo­
lytic anemia, or multiple fetuses. hat said, in impoverished
countries, routine multivitamin supplementation reduced the
incidence of low-birthweight and growth-restricted fetuses,
but did not alter preterm delivery or perinatal mortality rates
(Fawzi, 2007) .
Folic acid supplementation in early pregnancy can lower
neural-tube defect risks (Chap. 1 3, p. 270) . Namely, the CDC
(2004) estimated that the number of afected pregnancies had
decreased from 4000 pregnancies per year to approximately
3000 per year after mandatory fortiication of cereal products
with folic acid in 1 998. Perhaps more than half of all neural­
tube defects can be prevented with daily intake of 400 �g of
folic acid throughout the periconceptional period. Evidence
also suggests that folate insuiciency has a global efect on brain
development (Ars, 20 1 6) . Putting 1 40 �g of folic acid into each
1 00 g of grain products may increase the folic acid intake of
the average American woman of childbearing age by 1 00 �g/d.
Because nutritional sources alone are insuicient, however,
folic acid supplementation is still recommended (American
College of Obstetricians and Gynecologists, 20 1 6e) . Likewise,
the U.S. Preventive Services Task Force (2009) recommends
that all women planning or capable of pregnancy take a daily
supplement containing 400 to 800 �g of folic acid.
A woman with a prior child with a neural-tube defect can
reduce the 2- to 5-percent recurrence risk by more than 70
percent with a daily 4-mg folic acid supplement taken during
the month before conception and during the first trimester. As
emphasized by the American Academy of Pediatrics and the
American College of Obstetricians and Gynecologists (20 1 7) ,
this dose should b e consumed as a separate supplement and not
as multivitamin tablets. This practice avoids excessive intake of
fat-soluble vitamins.
Vitamin A, although essential, has been associated with con­
geni tal malformations when taken in high doses (> 1 0,000 IU / d)
during pregnancy. These malformations are similar to those
produced by the vitamin A derivative isotretinoin (Accutane),
which is a potent teratogen (Chap. 1 2, p. 245 ) . Beta-carotene,
the precursor of vitamin A found in fruits and vegetables, has
not been shown to produce vitamin A toxicity. Most prena­
tal vitamins contain vitamin A in doses considerably below
the teratogenic threshold. Dietary intake of vitamin A in the
United States appears to be adequate, and additional supple­
mentation is not routinely recommended. In contrast, vitamin
A deiciency is an endemic nutritional problem in the develop­
ing world (McCauley, 20 1 5) . Vitamin A deficiency, whether
overt or subclinical, is associated with night blindness and with
an increased risk of maternal anemia and spontaneous preterm
birth (West, 2003) .
Vitamin BJ2 plasma levels drop in normal pregnancy, mostly
as a result of reduced plasma levels of their carrier proteins­
transcobalamins. Vitamin B J 2 occurs naturally only in foods of
animal origin, and strict vegetarians may give birth to neonates
whose BI2 stores are low. Likewise, because breast milk of a
vegetarian mother contains little vitamin B 1 2, the deiciency
may become profound in the breastfed infant (Higginbottom,
1 978). Excessive ingestion of vitamin C also can lead to a
functional deiciency of vitamin B12. Although its role is still
controversial, vitamin B I 2 deiciency preconceptionally, similar
to folate, may elevate the risk of neural-tube defects (Molloy,
2009) .
Vitamin B6, which is pyridoxine, does not require supple­
mentation in most gravidas (Salam, 20 1 5) . For women at high
risk for inadequate nutrition, a daily 2-mg supplement is rec­
ommended. As discussed on page 1 74, vitamin B6, when com­
bined with the antihistamine doxylamine, is helpful in many
cases of nausea and vomiting of pregnancy.
Vitamin C allowances during pregnancy are 80 to 85 mg/ d­
approximately 20 percent more than when nonpregnant (see
Table 9-5) . A reasonable diet should readily provide this
amount, and supplementation is not necessary (Rumbold,
20 1 5) . Maternal plasma levels decline during pregnancy,
whereas cord-blood levels are higher, a phenomenon observed
with most water-soluble vitamins.
Vitamin D is a fat-soluble vitamin. After being metabolized
to its active form, it boosts the eiciency of intestinal calcium
absorption and promotes bone mineralization and growth.
Unlike most vitamins that are obtained exclusively from dietary
intake, vitamin D is also synthesized endogenously with expo­
sure to sunlight. Vitamin D deiciency is common during preg­
nancy. his is especially true in high-risk groups such as women
with limited sun exposure, vegetarians, and ethnic minorities­
particularly those with darker skin (Bodnar, 2007) . Maternal
deiciency can cause disordered skeletal homeostasis, congeni­
tal rickets, and fractures in the newborn (American College of
Obstetricians and Gynecologists, 20 1 7k) . Vitamin D supple­
mentation to women with asthma may decrease the likelihood
of childhood asthma in their fetuses (Litonjua, 20 1 6) . The Food
and Nutrition Board of the Institute of Medicine (20 1 1 ) estab­
lished that an adequate intake of vitamin D during pregnancy
and lactation was 1 5 �g/d (600 IU/d) . In women suspected of
having vitamin D deficiency, serum levels of 25-hydroxyvita­
min D can be obtained. Even then, the optimal levels in preg­
nancy have not been established (De-Regil, 20 1 6) .
• Pragmatic Nutritional Surveillance
Although researchers continue to study the ideal nutritional
regimen for the pregnant woman and her fetus, basic tenets for
the clinician include:
1 . Advise the pregnant woman to eat food types she wants in
reasonable amounts and salted to taste.
2. Ensure that food is amply available for socioeconomically
deprived women.
3. Monitor weight gain, with a goal of approximately 2 5 to
3 5 lb in women with a normal BMI.
4. Explore food intake by dietary recall periodically to discover
the occasional nutritionally errant diet.
5. Give tablets of simple iron salts that provide at least 27 mg
of elemental iron daily. Give folate supplementation before
and in the early weeks of pregnancy. Provide iodine supple­
mentation in areas of known dietary insuiciency.
6. Recheck the hematocrit or hemoglobin concentration at 28
to 32 weeks' gestation to detect signiicant anemia.
1 69
1 70
P reconce pti o n a l a n d P re nata l Ca re
TABLE 9-6. Some Contra i n d i catio ns to Exercise During P reg n a n cy
Sig n ifi ca nt card i ovasc u l a r or p u l m o na ry d i sease
S i g n ifi ca nt ri s k for p reterm labor: cerclage, m u ltifeta l gestation, s i g n ifi ca nt bleed i n g , t h reate ned preterm la bor, prematu rely
r u pt u red m e m b ra nes
Obstetrical com pl i cations: preecla m psia, p lacenta previa, a n e m i a, poorly contro l led d i abetes or epi lepsy, m o rb i d obesity,
feta l -g rowth restriction
S u m m a rized fro m America n Co l l ege of Obstet r i c i a n s a nd Gyn ecol og i sts, 201 7g.
COMMON CONCERNS
• Employment
More than half of the children in the United States are born
to working mothers. Federal law prohibits employers from
excluding women from job categories on the basis that they
are or might become pregnant. he Family and Medical Leave
Act of 1 993 requires that covered employers must grant up to
1 2 work weeks of unpaid leave to an employee for the birth
and care of a newborn child Qackson, 2 0 1 5). In the absence
of complications, most women can continue to work until the
onset of labor (American Academy of Pediatrics and the Ameri­
can College of Obstetricians and Gynecologists, 20 1 7) .
Some types o f work, however, may increase pregnancy com­
plication risks. Mozurkewich and colleagues (2000) reviewed
29 studies that involved more than 1 60,000 pregnancies. With
physically demanding work, women had 20- to 60-percent
higher rates of preterm birth, fetal-growth restriction, or ges­
tational hypertension. In a prospective study of more than 900
healthy nulliparas, women who worked had a ivefold risk of
preeclampsia (Higgins, 2002) . Newman and coworkers (200 1 )
reported outcomes i n more than 2900 women with singleton
pregnancies. Occupational fatigue-estimated by the number of
hours standing, intensity of physical and mental demands, and
environmental stressors-was associated with an increased risk
of preterm premature membrane rupture. For women reporting
the highest degrees of fatigue, the risk was 7.4 percent.
Thus, any occupation that subjects the gravida to severe
physical strain should be avoided. Ideally, no work or play is
continued to the extent that undue fatigue develops. Adequate
periods of rest should be provided. It seems prudent to advise
women with prior pregnancy complications that commonly
recur to minimize physical work.
• Exercise
In general, pregnant women do not need to limit exercise, pro­
vided they do not become excessively fatigued or risk injury
(Davenport, 20 1 6) . Clapp and associates (2000) reported that
both placental size and birthweight were signiicantly greater
in women who exercised. Duncombe and coworkers (2006)
reported similar findings in 1 48 women. In contrast, vfagann
and colleagues (2002) prospectively analyzed exercise behavior
in 750 healthy women and found that working women who
exercised had smaller infants and more dysfunctional labors.
The American College of Obstetricians and Gynecolo­
gists (20 1 7 g) advises a thorough clinical evaluation before
recommending an exercise program. In the absence of contra­
indications listed in Table 9-6, pregnant women are encour­
aged to engage in regular, moderate-intensity physical activity
for at least 1 50 minutes each week. Each activity should be
reviewed individually for its potential risk. Examples of safe
activities are walking, running, swimming, stationary cycling,
and low-impact aerobics. However, they should refrain from
activities with a high risk of falling or abdominal trauma. Simi­
larly, scuba diving is avoided because the fetus is at increased
risk for decompression sickness.
In the setting of certain pregnancy complications, it is wise
to abstain from exercise and even limit physical activity. For
example, some women with pregnancy-associated hypertensive
disorders, preterm labor, placenta previa, or severe cardiac or
pulmonary disease may gain from being sedentary. Also, those
with multiple or suspected growth-restricted fetuses may be
served by greater rest.
• Seafood Consumption
Fish are an excellent source of protein, are low in saturated
fats, and contain omega-3 fatty acids. The Avon Longitudinal
Study of Parents and Children reported beneicial efects on
pregnancy outcomes in women who consumed 340 g or more
of seafood weekly (Hibbeln, 2007) . Because nearly all fish and
shellish contain trace amounts of mercury, pregnant and lac­
tating women are advised to avoid specific types of ish with
potentially high methylmercury levels. These include shark,
swordfish, king mackerel, and tile fish. It is further recom­
mended that pregnant women ingest 8 to 1 2 ounces of fish
weely, but no more than 6 ounces of albacore or "white" tuna
(U.S. Environmental Protection Agency, 20 1 4) . If the mercury
content of locally caught fish is unknown, then overall fish con­
sumption should be limited to 6 ounces per week (American
Academy of Pediatrics and the American College of Obstetri­
cians and Gynecologists, 20 1 7) .
• Lead Screening
Maternal lead exposure has been associated with several adverse
maternal and fetal outcomes across a range of maternal blood
lead levels (Taylor, 20 1 5) . These include gestational hyper­
tension, miscarriage, low birthweight, and neurodevelopmen­
tal impairments in exposed pregnancies (American College of
Obstetricians and Gynecologists, 20 1 6c) . The levels at which
these risks rise remains unclear. However, recognizing that such
exposure remains a significant health issue for reproductive-aged
women, the CDC (20 1 Oa) has issued guidance for screening
P renata l Care
and managing exposed pregnant and lactating women. These
guidelines, which have been endorsed by the American College
of Obstetricians and Gynecologists (20 1 6c) , recommend blood
lead testing only if a risk factor is identified. If the levels are
> 5 /Lg1dL, then counseling is completed, and the lead source
is sought and removed. Subsequent blood levels are obtained.
Blood lead levels >45 Lg/dL are consistent with lead poisoning,
and women in this group may be candidates for chelation ther­
apy. Afected pregnancies are best managed in consultation with
lead poisoning treatment experts. National and state resources
are available at the CDC website: ww.cdc.gov/ncehllead/.
• Automobile and Air Travel
Pregnant women are encouraged to wear properly positioned
three-point restraints as protection against automobile crash
injury (Chap. 47, p. 927) . The lap portion of the restraining
belt is placed under the abdomen and across her upper thighs.
The belt should be comfortably snug. The shoulder belt also is
irmly positioned between the breasts. Airbags should not be
disabled for the pregnant woman.
In general, air travel in a properly pressurized aircraft has no
harmful efect on pregnancy (Aerospace Medical Association,
2003). Thus, in the absence of obstetrical or medical complica­
tions, the American Academy of Pediatrics and the American
College of Obstetricians and Gynecologists (20 1 6a, 20 1 7) have
concluded that pregnant women can safely ly up to 36 weeks'
gestation. It is recommended that pregnant women observe
the same precautions for air travel as the general population.
Seatbelts are used while seated. Periodic lower extremity move­
ment and at least hourly ambulation help lower the venous
thromboembolism threat. Signiicant risks with travel, espe­
cially international travel, are infectious disease acquisition and
development of complications remote from adequate health­
care resources (Ryan, 2002) .
• Coitus
In healthy pregnant women, sexual intercourse usually is not
harmul. Whenever miscarriage, placenta previa, or preterm labor
threatens, however, coitus is avoided. Nearly 1 0,000 women
enrolled in a prospective investigation by the Vaginal Infection
and Prematurity Study Group were interviewed regarding sex­
ual activity (Read, 1 993) . hey reported a decreased frequency
of coitus with advancing gestation. By 36 weeks, 72 percent
had intercourse less than once weekly. The decline is attributed
to lower desire and fear of harming the pregnancy (Bartellas,
2000; Staruch, 20 1 6) .
Intercourse speciically late in pregnancy i s n o t harm­
ful. Grudzinskas and coworkers ( 1 979) noted no association
between gestational age at delivery and coital frequency dur­
ing the last 4 weeks of pregnancy. Sayle and colleagues (200 1 )
reported no increased-and actually a decreased-risk o f deliv­
ery within 2 weeks of intercourse. Tan and associates (2007)
studied women scheduled for non urgent labor induction and
found that spontaneous labor ensued at equal rates in groups
either participating in or abstaining from intercourse.
Oral-vaginal intercourse is occasionally hazardous. Aronson
and Nelson ( 1 967) described a fatal air embolism late in pregnancy
as a result of air blown into the vagina during cunnilingus. Other
near-fatal cases have been described (Bernhardt, 1 988) .
• Dental Care
Examination of the teeth is included in the prenatal examina­
tion, and good dental hygiene is encouraged. Indeed, periodon­
tal disease has been linked to preterm labor. Unfortunately,
although its treatment improves dental health, it does not pre­
vent preterm birth (Michalowicz, 2006). Dental caries are not
aggravated by pregnancy. Importantly, pregnancy is not a con­
traindication to dental treatment including dental radiographs
(Giglio, 2009) .
• Immunization
Current recommendations for immunization during pregnancy
are summarized in Table 9-7. Well-publicized concerns regard­
ing a causal link between childhood exposure to the thimerosal
preservative in some vaccines and neuropsychological disorders
have led to some parents to vaccine prohibition. Although con­
troversy continues, these associations have proven groundless
(Sugarman, 2007; Thompson, 2007; Tozzi, 2009) . Thus, many
vaccines may be used in pregnancy. The American College of
Obstetricians and Gynecologists (20 1 6b) stresses the impor­
tance of integrating an efective vaccine strategy into the care
of both obstetrical and gynecological patients. The College fur­
ther emphasizes that information on the safety of vaccines given
during pregnancy is subject to change, and recommendations
can be found on the CDC website at ww. cdc.gov/vaccines.
he frequency of pertussis infection has substantially risen in
the United States. Young infants are at increased risk for death
from pertussis and are entirely dependent on passive immuniza­
tion from maternal antibodies until the infant vaccine series is
initiated at age 2 months. For this reason, a three-agent tetanus
toxoid, reduced diphtheria toxoid, and acellular pertussis (Tdap)
vaccine is recommended and is safe for pregnant women (Cen­
ters for Disease Control and Prevention, 20 1 3b, 20 1 6; Mor­
gan, 20 1 5) . However, as demonstrated by Healy and coworkers
(20 1 3) , maternal antipertussis antibodies are relatively short­
lived, and Tdap administration before pregnancy-or even in
the first half of the current pregnancy-is not likely to provide
a high level of newborn antibody protection. Thus, to maximize
passive antibody transfer to the fetus, a dose of Tdap is ideally
given to gravidas between 27 and 36 weeks' gestation (American
College of Obstetricians and Gynecologists, 20 1 7j; Centers for
Disease Control and Prevention, 20 1 3b, 20 1 6) .
All women who will b e pregnant during inluenza season
should be ofered vaccination, regardless of gestational age.
hose with underlying medical conditions that increase the
risk for infl u enza complications are provided the vaccine before
lu season starts. In addition to maternal protection against
infection, prenatal maternal vaccination in one study reduced
the infant infl u enza incidence in the irst 6 months of life by
63 percent (Zaman, 2008) . Moreover, it reduced all febrile
respiratory illnesses in these infants by a third.
Women who are susceptible to rubella during pregnancy
should receive measles, mumps, rubella (MMR) vaccination
postpartum. Although this vaccine is not recommended during
1 71
1 72
P reco n ce pti o n a l a n d P re nata l Care
TABLE 9-7. Reco m m endations for I m m u n ization D u ri n g Preg nancy
I m munobiological
Agent
Ind ications for
Immunization During
Pregnancy
Dose Schedule
Comments
Live Atten uated Virus Vacci nes
Measles
Contra i n d icated-see
i m m u ne g lobu l i ns
Si ng le dose SCI prefera bly as MMRa
Vacci nate suscepti ble women
postpartum . B reastfeedi ng is
not a co ntra i nd i cation
M u m ps
Contra i n dicated
Si n g le dose SCI prefera b ly as MMR
R u be l l a
Contra i n d i cated, b u t
congen ita l rubella
synd rome has never been
descri bed after vacci ne
Not routi nely recom m ended
for women i n the U n i ted
States, except women at
increased risk of expos u re b
Single dose SC, p refera bly as MMR
Vacci nate susceptible women
postpartum
Teratogenicity of vacci ne is
theoretical and not confi rmed
to date; vacci nate susceptible
women postpart u m
Vacci ne i n d i cated for susceptible
women t rave l i n g in endemic
a reas or i n other h i gh-risk
situations
Po! iomyel itis o ra l
= l ive
atte nuated;
i njection =
enha ncedpotency
i nactivated vi rus
P ri m a ry: Two doses of enha ncedpote ncy i nactivated v i ru s SC
at 4- to 8-week i nte rva l s a n d
a 3 rd dose 6-1 2 months after
2nd dose
I m mediate protection: One dose
o ra l po l i o vacci ne (in outbrea k
sett i ng)
Single dose SC
Yel l ow fever
Travel to h i g h-risk a reas
Va ricella
Contra i nd i cated, but no
adverse outco mes reported
in preg nancy
Two doses needed: 2nd dose
g iven 4-8 weeks after 1 st dose
Sma l l pox (vacci n ia)
Contra i n d icated in p reg nant
women a n d i n the i r
household co ntacts
One dose SCI m u ltiple pricks with
lancet
L i m ited theoretical risk
outweig hed by risk of yel low
fever
Teratogenicity of vacci ne is
theoretica l . Vacci nation of
susceptible women should be
considered postpa rtu m
Only vacci n e known to ca use feta l
harm
All preg nant women,
rega rd l ess of tri mester
d u ri ng fl u season
(October -May)
I n d ications for prophylaxis not
altered by preg nancy; each
case considered i n d iv i d u a l ly
One dose 1M every yea r
I nactivated virus vacc i ne
P u b l i c health a uthorities to be
consulted for i n d ications,
dosage, a n d route of
a d m i n i stration
Th ree-dose series 1M at 0, 1 , a n d
6 months
Ki l l ed-virus vaccine
Other
I n fl uenza
Rabies
H u ma n
pa p i l lomavirus
Not recom mended
Hepatitis B
P reexposure a n d
postexpos u re for women
at risk of i nfection, e.g.,
chronic l iver or kid ney
d isease
Th ree-dose series 1M at 0 , 1 , a nd
6 months
He patiti s A
P reexpos u re a n d
postexposu re if at risk
(i nternational travel);
chronic Ii fer d i sease
Two-dose sched u l e 1M, 6 months
a part
Polyva lent vacci nes avai lable
conta i n i n g i nactivated v i rus.
No teratogenicity has been
observed
Used with hepatitis B i m m u ne
g lobu l i n for some exposures.
Exposed newborn needs b i rthdose vacci nation a nd i m mune
g lobu l i n as soon as poss i ble.
All infa nts shou ld rece ive b i rth
dose of vacc i ne
I nactivated virus
P re nata l Ca re
TABLE 9-7. Conti n ued
Immunobiological
Agent
Indications for
Immunization During
Preg nancy
I nactivated Bacterial Vacci nes
Pneu mococcu s
I n d ications not altered by
preg nancy. Recommended
for wo men with asplen i a;
metabol ic, renal, ca rd iac,
or p u l mona ry d i seases;
i m m u n osu ppression; or
smokers
Meni ngococcus
I nd ications not a ltered by
preg nancy; vacci nation
recom mended in u n us u a l
outbreaks
Typhoid
Not recom mended rou t i nely
except for close, co nti n ued
expos u re or travel to
endemic areas
Anth rax
Toxoids
Teta n u s-d i p htheria­
ace l l u l a r pert u ss i s
(Tdap)
Chapter 64 (p. 1 228)
Recommended in every
preg nancy, prefera b ly
between 27 and 36 weeks
to max i m ize passive
a nti body transfer
Specific I m m une Globu l ins
Hepatitis B
Postexposu re prophylaxis
Rabies
Postexpos u re prophylaxis
Teta n u s
Postexposu re prophylaxis
Va ricella
Should be considered for
exposed preg nant women
to protect agai nst maternal,
not congen ital, i nfecti o n
Standard I m m u n e Globu l i n s
Hepatitis A:
Postexpos u re prophylaxis a n d
Hepatitis A
those a t h igh risk
virus vacci ne
shou l d be u sed
with hepatitis A
i m m u ne g lo b u l i n
Dose Schedule
Comments
I n a d u lts, one dose o n ly; consider
repeat dose i n 6 yea rs for high­
risk women
Polyva lent polysaccharide vacci ne;
safety in the fi rst tri mester has
not been eva l uated
One dose; tetrava lent vacci ne: two
doses for asplenia
A nt i m i crobial prophylaxis if
sign ificant exposu re
Ki l led
Primary: 2 i njections 1M 4 weeks
a pa rt
Booster: One dose; sched u l e not
yet determ i ned
S ix-dose primary vacci nation, then
a n n u a l booste r vacci nation
Ki l led, i njectable vacci ne or l ive
atten u ated ora l vacci ne. O ral
vacci ne preferred
P repa ration from ce l l-free fi ltrate
of B an thracis. No dead or l ive
bacteria. Teratoge n icity of
vacci ne theoretica l
P ri m a ry: Two doses 1 M at 1 -2
month i n terva l with 3 rd dose
6- 1 2 months ater the 2nd
Booster: Single dose 1 M every
1 0 yea rs, as a pa rt of wou n d
ca re if : 5 yea rs si nce last dose,
or once per preg nancy
Com b i ned teta n u s-d i phtheria
toxoids with ace l l u la r pert u ssis
(Tdap) p referred. U pdating
i m m u n e status should be part
of a ntepa rtu m ca re
Depends on exposu re
(Chap. 5 5 , p. 1 064)
U s u a l ly g ive n with hepatitis B virus
vacci ne; exposed newborn
needs i m med i ate p ro phylaxis
Used i n conj u nction with ra b i es
kil led-vi rus vacc i n e
Used i n conj u nction w i t h teta n u s
toxoid
I n d i cated a l so for newborns or
women who deve loped va ricel la
with i n 4 days before del ivery or
2 days fol lowi n g d e l ive ry
Half dose at i nj u ry site, half dose i n
deltoid
One dose 1M
One dose 1 M with i n 96 hours of
expos u re
0.02
m Ukg 1 M i n one dose
I m m u ne g lobu l i n s h o u l d be g iven
as soon as poss i b l e a n d with i n
2 weeks o f expos u re; i nfants
born to women who a re
i n c u bati n g the virus or a re
acutely i l l at del ivery s h o u l d
receive o n e dose of 0 . 5 m L as
soo n as poss i ble after b i rth
'Two doses n ecessa ry for students entering i nstitutions of h ig h er ed u cation, n ewly h i red medica l person nel, and t ravel a b road.
b l nactlvated pol io vacci n e recom mended for n on i m m u n ized a d u l ts at i n c reased risk.
10
i nt radermal ly; 1 M i nt ra m u s c u l a rly; M M R meas l es, m u m ps, ru bel l a; PO o ra l ly; SC s u bcuta neou sly.
F rom the Centers for Disease Control and P reve nt i o n, 20 1 1 ; Ki m, 2 0 1 6.
=
=
=
=
=
1 73
1 74
P reconceptio n a l a n d P re nata l Ca re
pregnancy, congenital rubella syndrome has never resulted from
its inadvertent use. Breastfeeding is compatible with MMR vac­
cination (Centers for Disease Control and Prevention, 20 1 l ) .
• Cafeine
Whether adverse pregnancy outcomes are related to cafeine
consumption is somewhat controversial. As summarized from
Chapter 1 8 (p. 348) , heavy intake of cofee each day-about
five cups or 5 00 mg of cafeine-slightly raises the miscarriage
risk. Studies of "moderate" intake-less than 200 mg daily­
did not fi n d a higher risk.
It is unclear if cafeine consumption is associated with pre­
term birth or impaired fetal growth. Clausson and coworkers
(2002) found no association between moderate cafeine con­
sumption of less than 500 mg/d and low birthweight, fetal­
growth restriction, or preterm delivery. Bech and associates
(2007) randomly assigned more than 1 200 pregnant women
who drank at least three cups of cofee per day to cafein­
ated versus decafeinated cofee. They found no diference in
birthweight or gestational age at delivery between groups. The
CARE Study Group (2008), however, evaluated 2635 low­
risk pregnancies and reported a l .4-fold risk for fetal-growth
restriction among those whose daily cafeine consumption
was > 200 mg/d compared with those who consumed < 1 00
mg/d. he American College of Obstetricians and Gynecolo­
gists (20 1 6d) concludes that moderate consumption of caf­
feine-less than 200 mg/ d-does not appear to be associated
with miscarriage or preterm birth, but that the relationship
between cafeine consumption and fetal-growth restriction
remains unsettled. The American Dietetic Association (2008)
recommends that cafeine intake during pregnancy be limited
to less than 300 mg/d, which approximates three 5 -oz cups of
percolated cofee.
• Nausea and Heartburn
Nausea and vomiting are common complaints during the first
half of pregnancy. These vary in severity and usually commence
between the first and second missed menstrual period and con­
tinue until 1 4 to 1 6 weeks' gestation. Although nausea and
vomiting tend to be worse in the morning-thus erroneously
termed morning sickness-both symptoms frequently continue
throughout the day. Lacroix and coworkers (2000) found that
nausea and vomiting were reported by three fourths of preg­
nant women and lasted an average of 35 days. Half had reliefby
14 weeks, and 90 percent by 22 weeks. In 80 percent of these
women, nausea lasted all day.
Treatment of pregnancy-associated nausea and vomiting
seldom provides complete relief, but symptoms can be mini­
mized. Eating small meals at frequent intervals is valuable. One
systematic literature search reported that the herbal remedy
ginger was likely efective (Borrelli, 2005). Mild symptoms usu­
ally respond to vitamin BG given along with doxylamine, but
some women require phenothiazine or H I -receptor blocking
antiemetics (American College of Obstetricians and Gynecolo­
gists, 2 0 1 5c) . In some with hyperemesis gravidarum, vomiting
is so severe that dehydration, electrolyte and acid-base distur­
bances, and starvation ketosis become serious problems.
Heartburn is another common complaint of gravidas and
is caused by gastric content reflux into the lower esophagus.
The greater frequency of regurgitation during pregnancy most
likely results from upward displacement and compression of
the stomach by the uterus, combined with relaxation of the
lower esophageal sphincter. Avoiding bending over or lying flat
is preventive. In most pregnant women, symptoms are mild
and relieved by a regimen of more frequent but smaller meals.
Antacids may provide considerable relief (Phupong, 20 1 5) .
Specifically, aluminum hydroxide, magnesium trisilicate, or
magnesium hydroxide is given alone or in combination. Man­
agement of heartburn or nausea that does not respond to sim­
ple measures is discussed in Chapter 54 (p. 1 045) .
• Pica and Ptyalism
The craving of pregnant women for strange foods is termed
pica. Worldwide, its prevalence is estimated to be 30 percent
(Fawcett, 20 1 6) . At times, nonfoods such as ice-pagophagia,
starch-amylophagia, or clay-geophagia may predominate.
This desire is considered by some to be triggered by severe iron
deficiency. Although such cravings usually abate after deficiency
correction, not all pregnant women with pica are iron deficient.
Indeed, if strange "foods" dominate the diet, iron deficiency
will be aggravated or will develop eventually.
Patel and coworkers (2004) prospectively completed a
dietary inventory on more than 3000 women during the sec­
ond trimester. The prevalence of pica was 4 percent. The most
common nonfood items ingested were starch in 64 percent, dirt
in 14 percent, sourdough in 9 percent, and ice in 5 percent.
he prevalence of anemia was 1 5 percent in women with pica
compared with 6 percent in those without it. Interestingly, the
rate of spontaneous preterm birth before 35 weeks was twice as
high in women with pica.
Women during pregnancy are occasionally distressed by
profuse salivation p yalism . Although usually unexplained,
ptyalism sometimes appears to follow salivary gland stimula­
tion by the ingestion of starch.
-
• Headache or Backache
At least 5 percent of pregnancies are estimated to be compli­
cated by new-onset or new-type headache (Spierings, 20 1 6) .
Common headaches are virtually universal. Acetaminophen is
suitable for most of these, and an in-depth discussion is found
in Chapter 60 (p. 1 057) .
Low back pain to some extent is reported by nearly 70 per­
cent of gravidas (Liddle, 20 1 5 ; Wang, 2004) . Minor degrees
follow excessive strain or significant bending, lifting, or walk­
ing. It can be reduced by squatting rather than bending when
reaching down, by using a back-support pillow when sitting,
and by avoiding high-heeled shoes. Back pain complaints
increase with progressing gestation and are more prevalent in
obese women and those with a history of low back pain. In
some cases, troublesome pain may persist for years after the
pregnancy (Noren, 2002).
Severe back pain should not be attributed simply to preg­
nancy until a thorough orthopedic examination has been con­
ducted. Severe pain has other uncommon causes that include
P renata l Care
pregnancy-associated osteoporosis, disc disease, vertebral osteo­
arthritis, or septic arthritis (Smith, 2008) . More commonly,
muscular spasm and tenderness are classiied clinically as acute
strain or ibrositis. Although evidence-based clinical research
directing care in pregnancy is limited, low back pain usually
responds well to analgesics, heat, and rest. Acetaminophen may
be used chronically as needed. Nonsteroidal antiinlammatory
drugs may also be beneicial but are used only in short courses
to avoid fetal efects (Chap. 1 2, p. 24 1 ) . Muscle relaxants
that include cyclobenzaprine or baclofen may be added when
needed. Once acute pain is improved, stabilizing and strength­
ening exercises provided by physical therapy help improve
spine and hip stability, which is essential for the increased load
of pregnancy. For some, a support belt that stabilizes the sacro­
iliac joint may be helpful (Gutke, 20 1 5) .
• Varicosities a n d Hemorrhoids
Venous leg varicosities have a congenital predisposition and
accrue with advancing age. They can be aggravated by factors
that raise lower extremity venous pressures, such as an enlarg­
ing uterus. Femoral venous pressures in the supine gravida
rise from 8 mm Hg in early pregnancy to 24 mm Hg at term.
Thus, leg varicosities typically worsen as pregnancy advances,
especially with prolonged standing. Symptoms vary from cos­
metic blemishes and mild discomfort at the end of the day to
severe discomfort that requires prolonged rest with feet eleva­
tion. Treatment is generally limited to periodic rest with leg
elevation, elastic stockings, or both. Surgical correction during
pregnancy generally is not advised, although rarely the symp­
toms may be so severe that injection, ligation, or even stripping
of the veins is necessary.
Vulvar varicosities frequently coexist with leg varicosities,
but they may appear without other venous pathology. Uncom­
monly, they become massive and almost incapacitating. If these
large varicosities rupture, blood loss can be severe. Treatment
is with specially itted pantyhose that will also minimize lower
extremity varicosities. With particularly bothersome vulvar var­
icosities, a foam rubber pad suspended across the vulva by a belt
can be used to exert pressure on the dilated veins.
Hemorrhoids are rectal vein varicosities and may irst appear
during pregnancy as pelvic venous pressures rise. Commonly,
they are recurrences of previously encountered hemorrhoids.
Up to 40 percent of pregnant women develop these (Poskus,
20 1 4) . Pain and swelling usually are relieved by topically
applied anesthetics, warm soaks, and stool-softening agents.
With thrombosis of an external hemorrhoid, pain can be con­
siderable. This may be relieved by incision and removal of the
clot following injection of a local anesthetic.
• Sleeping and Fatigue
Beginning early in pregnancy, many women experience fatigue
and need greater amounts of sleep. his likely is due to the
soporiic efect of progesterone but may be compounded in
the irst trimester by nausea and vomiting. In the latter stages,
general discomforts, urinary frequency, and dyspnea can be
additive. Sleep duration may be related to obesity and gesta­
tional weight gain (Facco, 20 1 6; Lockhart, 20 1 5) . Moreover,
sleep eiciency appears to progressively diminish as pregnancy
advances. Wilson and associates (20 1 1 ) performed overnight
polysomnography and observed that women in the third tri­
mester had poorer sleep eiciency, more awakenings, and less
of both stage 4 (deep) and rapid-eye movement sleep. Women
in the irst trimester were also afected, but to a lesser extent.
Daytime naps and mild sedatives at bedtime such as diphen­
hydramine (Benadryl) can be helpful.
• Cord Blood Banking
Since the irst successful cord blood transplantation in 1 988,
more than 2 5,000 umbilical cord blood transplantations have
been performed to treat hemopoietic cancers and various genetic
conditions (Butler, 20 1 1 ) . There are two types of cord blood
banks. Public banks promote allogeneic donation, for use by a
related or unrelated recipient, similar to blood product dona­
tion (Armson, 20 1 5) . Private banks were initially developed to
store stem cells for future autologous use and charged fees for
initial processing and annual storage. The American College of
Obstetricians and Gynecologists (20 1 5d) has concluded that if a
woman requests information on umbilical cord banking, infor­
mation regarding advantages and disadvantages of public versus
private banking should be explained. Some states have passed
laws that require physicians to inform patients about cord blood
banking options. Importantly, few transplants have been per­
formed by using cord blood stored in the absence of a known
indication in the recipient (Screnci, 20 1 6) . The likelihood that
cord blood would be used for the child or family member of
the donor couple is considered remote, and it is recommended
that directed donation be considered when an immediate family
member carries the diagnosis of a speciic condition known to be
treatable by hemopoietic transplantation (Chap. 56, p. 1 075).
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1 82
C H A PT E R 1 0
Feta l I m a g i n g
SONOGRAPHY IN OBSTETRICS . . . . . . . . . . . . . . . . . . . . 1 82
TEC H N OLOGY AND SAF ETY . . . . . . . . . . . . . . . . . . . . . . 1 82
G ESTATIONAL AGE ASSESSMENT . . . . . . . . . . . . . . . . . 1 83
FI RST-TRIMESTER SONOGRAPHY . . . . . . . . . . . . . . . . . . 1 85
S ECON D- AND TH IRD-TRIM ESTER SONOGRAPHY . . . . 1 86
CERVICAL LENGTH ASSESSMENT .
.
. . . . . . . . . . . . . . . . 1 89
NORMAL AND ABNORMAL F ETAL ANATOMY. . . . . . . . 1 9 1
DOPPLER . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 1 3
MAG N ETIC RESONANCE IMAGI NG . . . . . . . . . . . . . . . . . 2 1 5
After discovey of the Roentgen ray and the demonstration
of the various uses to which it might be put, it was thought
possible that it might also aord a valuable method ofinves­
tigating the shape and size of the pelvis.
- ] . Whitridge Williams ( 1 903)
X-ray techniques were j ust on the horizon when the first
edition of this textbook was published. he first application
focused on the maternal pelvis without attention to the fetus.
hus, congenital abnormalities were routinely not discovered
until birth. Subsequent radiographic eforts to evaluate the
fetus were later replaced by ultrasonography and more recently
by magnetic resonance (MR) imaging, techniques which have
become increasingly sophisticated. he subspecialty of fetal
medicine has developed only because of these advances, and
today's practitioner can hardly imagine obstetrical care without
them.
SONOGRAPHY IN OBSTETRICS
Prenatal sonography can be used to accurately assess gestational
age, fetal number, viability, and placental location, and it can
aid diagnosis of many fetal abnormalities. With improvements
in resolution and image display, anomalies are increasingly
detected in the irst trimester, and Doppler is used to manage
pregnancies complicated by growth impairment or anemia. he
American College of Obstetricians and Gynecologists (20 1 6)
recommends that prenatal sonography be performed in all
pregnancies and considers it an important part of obstetrical
care in the United States.
• Technology and Safety
The real-time image on the ultrasound screen is produced by
sound waves that are relected back from fluid and tissue inter­
faces of the fetus, amnionic fluid, and placenta. Sector array
transducers contain groups of piezoelectric crystals working
simultaneously in arrays. These crystals convert electrical energy
into sound waves, which are emitted in synchronized pulses.
Sound waves pass through tissue layers and are reflected back
to the transducer when they encounter an interface between tis­
sues of diferent densities. Dense tissue such as bone produces
high-velocity reflected waves, which are displayed as bright
echoes on the screen. Conversely, luid generates few relected
waves and appears dark. Digital images generated at 50 to more
than 1 00 frames per second undergo postprocessing that yields
the appearance of real-time imaging.
Ultrasound refers to sound waves traveling at a frequency
above 20,000 hertz (cycles per second) . Higher-frequency
transducers yield better image resolution, whereas lower fre­
quencies penetrate tissue more efectively. Transducers use
wide-bandwidth technology to perform within a range of
frequencies. In early pregnancy, a 5- to 1 0-megahertz (MHz)
transvaginal transducer usually provides excellent resolution,
Feta l l ma g i ng
because the early fetus is close to the transducer. And, in
the first and second trimesters, a 4- to 6-MHz transabdomi­
nal transducer is similarly close enough to the fetus to yield
precise images. By the third trimester, however, a lower fre­
quency 2- to 5-MHz transducer may be needed for tissue
penetration-particularly in obese patients-and this can lead
to compromised resolution.
Feta I Safety
Sonography should be performed o nly for a valid medical indi­
cation, using the lowest possible exposure setting to gain neces­
sary information-the AAA principle-as low as reasonably
4chievable. Examinations are performed only by those trained
to recognize fetal abnormalities and artifacts that may mimic
pathology, using techniques to avoid ultrasound exposure
beyond what is considered safe for the fetus (American College
of Obstetricians and Gynecologists, 20 1 6; American Institute
of Ultrasound in Medicine, 20 1 3b) . No causal relationship has
been demonstrated between diagnostic ultrasound and any rec­
ognized adverse efect in human pregnancy. The International
Society of Ultrasound in Obstetrics and Gynecology (20 1 6)
further concludes that there is no scientifically proven associa­
tion between ultrasound exposure in the first or second trimes­
ters and autism spectrum disorder or its severity.
All sonography machines are required to display two indices:
the thermal index and the mechanical index. The thermal index
is a measure of the relative probability that the examination
may raise the temperature, potentially high enough to induce
injury. That said, fetal damage resulting from commercially
available ultrasound equipment in routine practice is extremely
unlikely. The potential for temperature elevation is higher with
longer examination time and is greater near bone than in soft
tissue. heoretical risks are higher during organogenesis than
later in gestation. The thermal index for soft tissue, Tis, is used
before 1 0 weeks' gestation, and that for bone, ib, is used at or
beyond 1 0 weeks' (American Institute of Ultrasound in Medi­
cine, 20 1 3b) . The thermal index is higher with pulsed Doppler
applications than with routine B-mode scanning (p. 2 1 3) . In
the first trimester, if pulsed Doppler is clinically indicated, the
thermal index should be ;0.7, and the exposure time should
be as brief as possible (American Institute of Ultrasound in
Medicine, 20 1 6) . To document the embryonic or fetal heart
rate, motion-mode (M-mode) imaging is used instead of pulsed
Doppler imaging.
The mechanical index is a measure of the likelihood of adverse
efects related to rarefactional pressure, such as cavi tation­
which is relevant only in tissues that contain air. Microbubble
ultrasound contrast agents are not used in pregnancy for this
reason. In mammalian tissues that do not contain gas bodies, no
adverse efects have been reported over the range of diagnostically
relevant exposures. Because fetuses cannot contain gas bodies,
they are not considered at risk.
The use of sonography for any nonmedical purpose, such as
"keepsake fetal imaging," is considered contray to responsible
medical practice and is not condoned by the Food and Drug
Administration (20 1 4) , the American Institute of Ultrasound
in Medicine (20 1 2, 20 1 3b) , or the American College of Obste­
tricians and Gynecologists (20 1 6) .
Operator Safety
The reported prevalence of work-related musculoskeletal dis­
comfort or injury among sonographers approximates 70 percent
Ganga, 20 1 2; Roll, 20 1 2) . The main risk factors for injury dur­
ing transabdominal ultrasound examinations are awkward pos­
ture, sustained static forces, and various pinch grips used while
maneuvering the transducer (Centers for Disease Control and
Prevention, 2006) . Maternal habitus can be contributory because
more force is oten employed when imaging obese patients.
The following guidelines may help avert injury:
1 . Position the patient close to you on the examination table.
As a result, your elbow is close to your body, shoulder abduc­
tion is less than 30 degrees, and your thumb is facing up.
2. Adjust the table or chair height so that your forearm is paral­
lel to the floor.
3. If seated, use a chair with back support, support your feet,
and keep ankles in neutral position. Do not lean toward the
patient or monitor.
4. Face the monitor squarely and position it so that it is viewed
at a neutral angle, such as 1 5 degrees downward.
5 . Avoid reaching, bending, or twisting while scanning.
6. Frequent breaks may prevent muscle strain. Stretching and
strengthening exercises can be helpful.
• Gestational Age Assessment
The earlier that sonography is performed, the more accurate
the gestational age assessment. Specific criteria for "re-dating" a
pregnancy, that is, reassigning the gestational age and estimated
date of delivery using initial sonogram findings, are shown in
Table 1 0- 1 . The only exception to revising the gestational age
based on early sonography is if the pregnancy resulted from
assisted reproductive technology, in which case accuracy of ges­
tational age assessment is presumed.
Sonographic measurement of the crown-rump length (CRL)
is the most accurate method to establish or conirm gestational
TABLE 1 0- 1 . Sonog ra p h i c Gestational Age Assessment
Gestational Age
<9 wks
9 to < 1 4 wks
1 4 to < 1 6 wks
1 6 to < 22 wks
22 to < 28 wks
: 2 8 wee ks
Para meter(s)
Threshold
to Revisea
CRL
CRL
B PO,
B P O,
B PO,
B P Ot
>5 d
>7 d
>7 d
>10 d
>14 d
>21 d
HC
HC
HC
HC
AC
AC
AC
AC
FL
FL
FL
FL
aSonog ra p h i c gestati o n a l a g e s h o u l d be used when t h e
LM P-d e rived gestat i o n a l age d iffers from t h a t o bta i n e d
w i t h sonog ra phy by the t h reshold va l ue.
AC a bdom i na l ci rcu mference; B P O b i pa r i etal d i a m eter;
C R L crown-ru m p l ength; FL fem u r length; HC h ead
c i rcu mference; LM P l a st m e n strual period.
Mod ified from American Col lege of Obstetri c i a n s a nd
Gyn eco lo g i sts, 20 1 7 b.
=
=
=
=
=
=
1 83
1 84
The Feta l Patient
FIGURE 1 0-1 The measu red crown-ru m p length in this 1 2-week
3-day fetus a pproxi mates 6 cm.
age (Appendix, p. 1 263) . As noted, transvaginal imaging typi­
cally yields higher resolution images. The CL is measured
'
in the midsagittal plane with the embryo or fetus in a neu­
tral, nonlexed position so that its length can be measured in
a straight line (Fig. 1 0- 1 ) . The measurement should include
neither the yolk sac nor a limb bud. The mean of three discrete
measurements is used. Until 1 3 6/7 weeks' gestation, the CL is
accurate to within 5 to 7 days (American College of Obstetri­
cians and Gynecologists, 20 1 7b) .
Starting at 1 4°/ weeks, equipment software formulas calculate
estimated gestational age and fetal weight from measurements
of the biparietal diameter, head and abdominal circumference,
and femur length (Fig. 1 0-2) . The estimates are most accurate
when multiple parameters are used but may over- or underes­
timate fetal weight by up to 20 percent (American College of
Obstetricians and Gynecologists, 20 1 6) . Various nomograms
for other fetal structures, including the cerebellar diameter, ear
length, ocular distances, thoracic circumference, and lengths of
kidney, long bones, and feet, may be used to address speciic
questions regarding organ system abnormalities or syndromes
(Appendix, p. 1 266) .
The biparietal diameter (BPD) most accurately reflects ges­
tational age, with a variation of 7 to 1 0 days in the second
trimester. The BPD is measured perpendicular to the midline
falx in the transthalamic view, at the level of the thalami and
cavum septum pellucidum (CSP) (see Fig. 1 0-2A) . Calipers are
placed from the outer edge of the skull in the near ield to the
inner edge of the skull in the far field. he head circumference
(HC) is also measured in the trans thalamic view. An ellipse is
FIGURE 1 0-2 Feta l biometry. A. Tra nsth a l a m i c view. A tra nsverse
(axial) image of the head is obta i ned at the level of the cavum
sept u m pell ucid u m (arrows) a nd thalami (asterisks). The biparieta l
dia mete r is measu red perpendicu lar to the sag itta l m i d l i ne, from the
outer edge of the sku l l i n the nea r field to the i n ner edge of the sku l l
i n t h e fa r field. B y convention, t h e near field is that which i s closer to
the sonog ra p h ic tra nsd ucer. The head circu mference is measu red
circu mferentia l ly a round the outer border of the sku l l. B. Fem u r
length. T h e fem u r is measured perpendiCUlar t o the femora l shaft,
from each dia physea l end, excl uding the epi physis. C. Abdominal
ci rcu mference. This is a transverse mea s u rement at the level of the
stomach (5). The J-sha ped structu re (arrowheads) i n d icates the con­
fl uence of the u m b i l ical vei n and the right porta l vein. Idea l ly, o n ly
one rib is visible on each side of the a bdomen, i n d icati ng that the
i mage was not taken at a n oblique a ng le.
Feta l l m a g i n g
placed around the outer edge of the skull or the circumference
is calculated using BPD and occipital-frontal diameter (OFD)
values. he cephalic index, which is the BPD divided by the
OFD, is normally 70 to 86 percent.
If the head shape is lattened-dolichocephay, or rounded­
brachycephay, the HC is more reliable than the BPD. hese
head shape variants may be normal or can be secondary to fetal
position or oligohydramnios. But, dolichocephaly can occur
with neural-tube defects, and brachycephaly may be seen in
fetuses with Down syndrome. lso, with abnormal skull shape,
craniosynostosis and other craniofacial abnormalities are a con­
sideration.
he femur length (FL) correlates well with both BPD and
gestational age. It is measured with the beam perpendicular to
the long axis of the shat. Calipers are placed at each end of the
calcified diaphysis and exclude the epiphysis. For gestational age
estimation, it has a variation of 7 to 1 1 days in the second trimes­
ter (see Fig. 1 O-2B). A femur measurement that is < 2. 5th per­
centile for gestational age or that is shortened to :;90 percent of
that expected based on the measured BPD is a minor marker for
Down syndrome (Chap. 1 4, p.287). he normal range for the FL
to abdominal circumference (AC) ratio is generally 20 to 24 per­
cent. A dramatically foreshortened FL or a FL-to-AC ratio below
1 8 percent prompts evaluation for a skeletal dysplasia (p. 2 1 0) .
O f biometric parameters, A C is most afected b y fetal
growth. Thus, for gestational age estimation, AC has the great­
est variation, which can reach 2 to 3 weeks in the second
trimester. To measure the AC, a circle is placed outside the
fetal skin in a transverse image that contains the stomach and
the confluence of the umbilical vein with the portal sinus (see
Fig. 1 0-2C) . The image should appear as round as possible and
ideally contains no more than 1 rib on each side of the abdo­
men. he kidneys should not be visible in the image.
Variability of the sonographic gestationl age estimate
increases with advancing gestation. Accordingly, pregnancies not
imaged prior to 22 weeks to conirm or revise gestational age are
considered suboptimaly ated (American College of Obstetricians
and Gynecologists, 20 1 7a) . Although the estimate is improved
by averaging multiple parameters, if one parameter difers
TABLE 1 0-2. S o m e I n d ications for First-Tri m ester
Ultrasou n d Exa m ination
Confi rm a n i ntra u terine p reg n a n c!
Eva l u ate a suspected ectop ic p reg n a n cy
Defi ne the c a u s e of vag i n a l bleed i n g
Eva l uate pelvic pa i n
Est i m ate g estationa l age
Diag nose o r eva l uate m u lt ifeta l gestations
C o n fi rm ca rdiac activity
Ass i st c h o ri o n i c vi l l u s sa m p l ing, em bryo tra n sfer, and
l oca l izat i o n a n d re m ova l of a n i ntra uteri n e device
Assess for certa i n feta l a n o ma l i es, such as a ne n cepha ly, i n
h ig h-risk ' atients
Eva l u ate m atern a l pe lvic m a sses a n d/or uterine
a bnor m a I ities
Measu re n u c h a l tra n s l ucency /hen pa rt of a scree n i n g
p rog ra m for feta l a neu ploidy
Eva l uate s u s oected gestati o n a l trophoblastic d i sease
Mod i fied from the American I n s titute of U ltrasound i n
Med i c i n e, 2 0 1 3a .
significantly from the others, consideration should be given to
excluding it from the calculation. he outlier may result from
poor visibility, but it could also indicate a fetal abnormality or
growth problem. Reference tables such as the one in the Appendix
(p. 1 264) may be used to estimate fetal weight percentiles.
• First-Trimester Sonography
Indications for sonography before 1 4 weeks' gestation are listed
in Table 1 0-2. Early pregnancy can be evaluated using trans­
abdominal or transvaginal sonography, or both. he compo­
nents listed in Table 1 0-3 should be assessed. First-trimester
sonography can reliably diagnose anembryonic gestation,
embryonic demise, ectopic pregnancy, and gestational tro­
phoblastic disease. he irst trimester is also the ideal time to
evaluate the uterus, adnexa, and cul-de-sac. Determination of
TABLE 1 0-3. Com po n e nts of Sta ndard U ltraso u n d Exa m i nation by Tri m ester
First Tri mester
Second and Third Tri mester
Gestationa l sac s i ze, l ocation, a nd n u m be r
E m b ryo a n d/or yo l k s a c identification
Crown-ru m p l e ngth
Feta l n u m ber, i n c l u d i ng a m n ion i city a n d chorionicity of
m u ltieta l gestations
E m b ryon i c/feta l card ia c activity
Assessment of e m b ryon i /feta l a natomy a ppropriate fo r
the fi rst ri mester
Eva l uation of the maternal u terus, a d nexa, a n d
cu l-de-sac
Eva l uat"on of the feta l n u c h a l reg i on, with conside ration of
feta l :cha l tra n s l ucenry a ssessm ent
Feta l n u m ber, i n c l u d i n g a m n io n i city a nd chorionicity of
m u ltifeta l g estations
Feta l ca rd iac activity
Feta l p resentation
P lacental l ocation, a p peara n ce, a nd relatio n s h i p t o tie
i nterna l cervica l os, with docu m entati o n of placental c o rd
i nsertion s ite when tech n ic a l l y possi ble
A m n i o n ic fl u id vol u me
Gestati o n a l age a ssessment
Feta l wei g h t estimation
Feta l a natom ica l su rvey, i n c l u d i ng docu m entation of
tec h n ical l i m i tations
Eva l uation of the maternal uterus, adnexa, a n d cervix w h e n
a p propriate
Mod i fied fro m the Ame rica n I n stitute of U ltraso u n d in M ed i c i ne, 20 1 3a .
1 85
1 86
The Feta l Pat i e n t
chorionicity in a multifetal gestation
is most accurate in the first trimester
(Chap. 45, p. 868) .
n intrauterine gestational sac is reli­
ably visualized with transvaginal sonog­
raphy by 5 weeks, and an embryo with
cardiac activity by 6 weeks (Fig. 1 0-3) .
The embryo should b e visible transvagi­
nally once the mean sac diameter has
reached 25 mm-otherwise the gesta­
tion is anembyonic. Cardiac motion is
usually visible with transvaginal imaging
when the embryo length reaches 5 mm.
In embryos <7 mm without cardiac
activity, subsequent examination may
FIGURE 1 0-3 A. The measu red crown-ru m p length is a p p roxi mately 7 mm in this 6-week
e m b ryo. B. M-mode demonstrates em bryonic cardiac activity a nd a hea rt rate of 1 24 beats
be needed to determine viability (Amer­
per m i n ute.
ican College of Obstetricians and Gyne­
cologists, 20 1 6) . At Parkland hospital,
should not replace second-trimester anatomical evaluation (Amer­
first-trimester demise is diagnosed if the embryo has reached
ican College of Obstetricians and Gynecologists, 20 1 6).
1 0 mm and lacks cardiac motion. Other criteria for this diagno­
As examples, in one study of more than 40,000 pregnancies
sis are found in Chapter 1 8 (Table 1 8-3, p. 350).
undergoing sonographic aneuploidy screening between 1 1 and
N uc h a l Tra n s l ucency
1 4 weeks, basic anatomical evaluation yielded a detection rate
of
approximately 40 percent for structural abnormalities (Syn­
Nuchal translucency (NT) evaluation is a component of
gelaki,
20 1 1 ) . Bromley and colleagues (20 1 4) similarly found
first-trimester aneuploidy screening, discussed in Chapter 1 4
that
late
irst-trimester sonography identiied major abnormali­
(p. 28 1 ) . I t represents the maximum thickness o f the subcuta­
ties
in
0.5
percent of pregnancies, representing approximately
neous translucent area between the skin and soft tissue overly­
40
percent
of pregnancies with anomalies detected prenatally.
ing the fetal spine at the back of the neck. NT is measured in
Detection
rates
are very high for anencephaly, alobar holopros­
the sagittal plane between 1 1 and 14 weeks' gestation using
encephaly,
and
ventral
wall defects. But, in one analysis of more
precise criteria (Table 1 0-4) . When the NT measurement
than
60,000
pregnancies
with these early scans, only a third of
is increased, the risk for fetal aneuploidy and various struc­
major
cardiac
anomalies
were
identiied, and no cases of micro­
tural anomalies-in particular heart defects-is signiicantly
cephaly,
agenesis
of
the
corpus
callosum, cerebellar abnormali­
elevated.
ties, congenital pulmonary airway malformations, or bowel
obstruction were detected (Syngelaki, 20 1 1 ) . In another study
Feta l A n o m a l y Detection
of low-risk or unselected pregnancies, 32 percent of anomalies
Assessment for selected fetal abnormalities in an at-risk pregnancy
were detected, whereas in pregnancies described as high-risk,
is done with irst-trimester sonography (see Table 1 0-2) . Research
anomaly detection exceeded 60 percent (Karim, 20 1 7) .
in this area has focused on anatomy visible at 1 1 to 1 4 weeks'
gestation, to coincide with sonography performed as part of aneu­
• Second- a n d Third-Trimester Sonography
ploidy screening. ith current technoloy, it is not realistic to expect
that all major abnomalities detectable in the second trimester may
be visualized in the irst trimester. Thus, irst-trimester scanning
It is recommended that sonography be routinely ofered to all
pregnant women between 1 8 and 22 weeks' gestation (American
TABLE 1 0-4. G u idel i nes for N uc h a l Tra nsl ucency (NT) Mea s u rement
The m a rg i n s of NT edges m ust be clear e n o u g h for proper ca l i pe r pl acement
The fetu s m u st be i n the m id sag itta l p l a n e
T h e i mage m u st be m a g n ified so that i t i s fi l led b y the feta l h e a d , neck, a n d u pper thorax
The feta l neck m u st be in a neutra l position, not flexed and n ot hyperexte nded
The a m n ion m u st be seen as sepa rate from the NT l i n e
Electro n i c cal i pe rs m u st be u sed t o perform t h e m ea s u rement
The + ca l i pe rs m u st be pl aced on the i n ner bord e rs of the n uc h a l space with n o ne of the
horizonta l crossbar itself p rotru d i n g i nto the space
The ca l i pers m u st be placed perpend i c u l a r to the long axis of the fet u s
The mea s u rement m u st be o bta i ned at the wid est s pace o f the N T
F ro m the America n I n stitute o f U lt rasou n d i n Med i c i ne, 20 1 3a, with permission .
Feta l l m a g i ng
TABLE 1 0-5. Some I n d i cations for Second- or Th i rd­
Tri mester U ltrasound Exa m i nation
Maternal I nd ications
Vag i n a l b l eed i n g
Abdo m i n a l/pelvic pa i n
Pelvic mass
Suspected ute r i ne a bnormal ity
S u s pected ecto pic p reg na n cy
S u spected m o l a r p reg na ncy
S u spected p l acenta previa and su bseq uent s u rvei l l a n ce
S u s pected p l a ce nta l a b ru ption
Preterm prematu re ru pture of membranes and/or preterm labor
Cervical i n s u ffi c i e n cy
Adj u nct to cervica l cerclage
Adj u nct to a m n iocentesis o r other proced u re
Adj u nct to external cep h a l ic ve rsion
Feta l I ndications
Gestationa l a g e est i mation
Feta l -g rowth eva l u ation
Sig n ifica nt u te r i n e size/cl i n ical date d i screpa n cy
S u spected m u ltifeta l gestation
Feta l a nato m i c a l eva l uation
Feta l a n o m a ly scree n i n g
Assessment for fi nd i ng s t h a t ra ise t h e a n e u ploidy risk
Abnormal biochem ica l ma rkers
Feta l prese ntati o n determ i nation
S u s pected hyd ra m n ios o r o l ig ohyd ra m n ios
Feta l we l l- be i n g eva l uation
Fol l ow-u p eva l uation of a feta l a no m a ly
H i story of cong e n ita l a no m a ly i n prior preg na ncy
S u spected feta l d eath
Feta l cond ition eva l uation i n late reg istra nts for prenata l ca re
Ada pted fro m the American I n stitute of U lt rasou n d i n
Med i c i ne, 2 0 1 3a.
College of Obstetricians and Gynecologists, 20 1 6) . This time
interval permits accurate assessment of gestational age, fetal anat­
omy, placental location, and cervical length. Recognizing that
the gestational age at which abnormalities are identified may
afect pregnancy management options, providers may opt to per­
form the examination prior to 20 weeks. The many additional
indications for second- and third-trimester sonography are listed
in Table 1 0-5 . The three examination types are standard, special­
ized-which includes targeted sonography, and limited.
The standard sonogram includes evaluation of fetal number
and presentation, cardiac activity, amnionic fl u id volume, pla­
cental position, fetal biometry, and fetal anatomy (American
Institute of Ultrasound in Medicine, 20 1 3b) . When techni­
cally feasible, the maternal cervix and adnexa are examined as
clinically appropriate. Components are found in Table 1 0-3,
and the fetal anatomical structures that should be evaluated
are listed in Table 1 0-6. With twins or other multiples, docu­
mentation also includes the number of chorions and amnions,
comparison of fetal sizes, estimation of amnionic luid volume
within each sac, and fetal sex determination (Chap. 45, p. 868) .
he targeted sonogram is a type of specialized examination. It is
performed when the risk for a fetal anatomical or genetic abnor­
mality is elevated because ofhistory, screening test result, or abnor­
mal inding during standard examination (Table 1 0-7) . Targeted
sonograms include a detailed anatomical survey, the components
ofwhich are shown in Table 1 0-6. Because it carries the CPT code
768 1 1 , this sonogram is colloquilly called the "768 1 1 examina­
tion." It is intended to be indication-driven and should not be
repeated later in the absence of an extenuating circumstance.
Physicians who perform or interpret targeted sonograms should
have expertise in fetal imaging, through both training and ongo­
ing experience (Wax, 20 1 4) . For many of the targeted examina­
tion components, the physician determines on a case-by-case basis
whether assessment is needed (American College of Obstetricians
and Gynecologists, 20 1 6). Other types of specilized examinations
include fetal echocardiography, Doppler evaluation, and the bio­
physical proile, which is described in Chapter 1 7 (p. 337).
A limited sonogram is performed to address a speciic clini­
cal question. Examples include evaluation of fetal presentation,
viability, amnionic luid volume, or placental location. In the
absence of an emergency, a limited examination is only per­
formed if a standard sonogram has already been completed.
Otherwise, provided that the gestational age is at least 1 8 weeks,
a standard sonogram is recommended.
Feta l Anomaly Detection
With current advances in imaging technology, approximately
50 percent of major fetal abnormalities overall are detected
with standard sonography (Rydberg, 20 1 7) . he sensitivity of
sonography for detecting fetal anomalies varies according to
factors such as gestational age, maternal habitus, fetal position,
equipment features, examination type, operator skill, and the
speciic abnormality in question. For example, maternal o besity
has been associated with a 20-percent reduction in the anomaly
detection rate (Dashe, 2009) .
Detection also varies considerably according to the abnormality.
For example, population-based data from 1 8 registries comprise
the EUROCAT network. Between 20 1 1 and 20 1 5, EUROCAT
(20 1 7) prenatal detection rates for selected fetal anomalies­
excluding genetic conditions-were as follows: anencephaly, 99
percent; spina bifida, 89 percent; hydrocephaly, 78 percent; clet
lip/palate, 68 percent; hypoplastic let heart, 87 percent; transposi­
tion of the great vessels, 64 percent; diaphragmatic hernia, 74 per­
cent; gastroschisis, 94 percent; omphalocele, 92 percent; bilateral
renal agenesis, 94 percent; posterior urethral valves, 79 percent;
limb-reduction defects, 57 percent; and clubfoot, 57 percent.
Importantly, however, the overall anomaly detection rate,
excluding aneuploidy, was below 40 percent. his relects inclu­
sion of anomalies with minimal or no sonographic detection
in the second trimester, such as microcephaly, choanal atresia,
cleft palate, Hirschsprung disease, anal atresia, and congeni­
tal skin disorders. hese are mentioned because clinicians tend
to focus on abnormalities amenable to sonographic detection,
whereas those not readily detectable may be equally devastat­
ing to families. Therore, evey sonographic examination should
include a frank discussion of examination limitations.
Most anomalous neonates are born to women whose preg­
nancies are otherwise considered low-risk, that is, without an
1 87
1 88
The Fetal Patient
TABLE 1 0-6. Components of Sta n d a rd a nd Ta rgeted Feta l Anato m i c S u rveys
Additional Targeted (Detai led)
Sonogram Components
Standard Sonogram
Head, face, and neck
Latera l cerebr a l ventricles
Choro i d plexu s
M i d l i ne fa lx
Cav u m sept u m pel l uc i d u m
Cerebe l l u m
C i stena magna
U ppe r l i p
Consid eration of n u c h a l skin fo ld meas u rement
at 1 5-20 weeks
Head, face, and neck
I nteg r ity and shape of c ra n i u m
Th i rd ve ntr iclea
Fourth ventri clea
Corpu s cal losuma
Cerebe l l a r l o bes, ver m i s
Bra i n parenchyma
P rofi l e
Coronal nose, l i ps, l e n sa
Palatea, maxi l la, m a n d i b l e, a n d to n g u ea
Ear pOSition and s izea
Orbitsa
N eck
Chest
Cardiac activity
Fou r-c h a m be r view of the heart
Left ve ntric u l a r o utflow tract
R i g h t ventri c u l a r outflow tract
Chest
Aortic a rch
S u perior/i nferior venae cavae
3-vessel view
3-vessel a n d trachea view
Lungs
I n teg rity of d i a ph ra g m
R i bsa
Abdomen
Stomach: presence, size, and situs
Ki d neys
U ri na ry bladder
U m b i l ical cord i n sertion i nto fetal a bd o m e n
U m b i l ica l cord vesse l n u m be r
Abdomen
S m a l l and l a rge bowela
A d re n a l g l a n d sa
G a l l bladdera
Liver
Re nal arteri esa
Spleen°
I nteg rity of a bdom i n a l wa l l
Spine
Cervica l, thoracic, l u m ba r, a n d sacra l spi n e
Spine
Shape a n d c u rvatu re
I nteg rity of s p i n e a n d overlying soft tissue
Extrem ities
Legs and a rms
Extremities
A rc h itectu re, position, n u m be r
H a nd s
Feet
D i g itsa: n u m ber, position
Feta l sex
I n m u ltifeta l gestations and when medically i nd icated
aWhe n m ed i ca l ly i nd i cated (determ i n ed on case-by-case bas i s).
Mod ifi ed fro m the American I n stitute of U ltra so u nd i n Med i c i ne, 2 0 1 3a; Wax, 20 1 4.
indication for targeted sonography. hus, for standard sonographic
examinations, accurate documentation and quality assurance are
essential to optimize detection rates. Practice guidelines and stan­
dards established by organizations such as the American Institute
of Ultrasound in Medicine (20 1 3b) and the Internationl Society
of Ultrasound in Obstetrics and Gynecology (Salomon, 20 1 1 )
have undoubtedly contributed to improvements in anomaly detec­
tion rates. Ultrasound practice accreditation is a process ofered
by the American Institute of Ultrasound in Medicine and the
American College of Radiology that was developed to improve
imaging quality and adherence to guidelines. It includes review of
images and their storage, ultrasound equipment, report generation,
and the qualifications of physicians and sonographers. The Society
for Maternal-Fetal Medicine (20 1 3) recommends that whenever
possible, obstetrical ultrasound examinations by maternal-fetal
medicine subspecialists be performed by accredited practices.
A m n ion ic F l u id Vol u m e
Evaluation o f amnionic luid volume is a component o f every
second- or third-trimester sonogram, and volumes vary with
Feta l l m a g i ng
TABLE 1 0-7. I nd icatio n s for Ta rgeted F eta l Anatom ica l U ltrasound Exa m i nation
Prior fetus or neonate with a structura l or genetic/chromosomal a bnormal ity
Cu rrent pregnancy with known or suspected fetal a bnormal ity or confirmed growth abnormality
I ncreased risk for fetal structural a nomaly in current preg na ncy
Maternal d ia betes d iag nosed before 24 weeks' ges