PREGNANCY:
st
nd
1 and 2 Trimesters
(0 – 24 weeks)
I. General
A. Sonography used after 4-5 weeks
B. Events prior to this time:
1. Ovulation
2. Fertilization
3. Implantation
4. Placentation
5. Embryonic Development
II. OVULATION
A. Definition: a cyclic event controlled
by two hormones (FSH and LH) that
occurs monthly
1. ~ 20 ova begin maturing
2. Only one completes the
maturation process
Phase??
1st & 2nd Trimesters, Ovulation, con’t.
3. After ovulation, ovum moves into
uterine tube
4. If fertilized, the zygote
begins to divide
5. Implantation begins in ~6 days
III. FERTILIZATION
A. Definition: penetration of the ovum
by one spermatozooan
1. Hyaluronidase (from acrosome):
enzyme that allows penetration
2. Lack of acrosome/enzyme: infertility
3. Polyspermy: More than one sperm
penetrates ovum
1st & 2nd Trimesters, Fertilization con’t.
B. Sperm and ovum are haploid (N)
C. Genetic material in nuclei fuses to
form zygote (2N)
D. Zygote begins cell division (mitosis!)
immediately
1st & 2nd Trimesters, Fertilization con’t.
E. Differentiation: prior to reaching
uterus, zygote has developed into
morula
F. Cells continue to divide, form
blastula or blastocyst
1. trophoblast
2. inner cell mass or blastoderm
1st & 2nd Trimesters, Fertilization, con’t.
G. Trophoblast will give rise to placenta
H. Inner cell mass will give rise to the embryo
1. Ectoderm (outer layer or “outer skin”)
2. Endoderm (inner layer or “inner skin”)
3. Mesoderm (middle layer or “middle skin”)
Primary Germ Layers

Trophoblast Cells


Give rise to placenta
Primary germ layers:



Ecotderm
Mesoderm
Endoderm
IV. Implantation
A. Uterus composed of 3 layers
1. Perimetrium: external layer
- peritoneum/broad ligament
2. Myometrium: middle layer
3. Endometrium: inner layer
The Uterus
Perimetrium
Myometrium
Endometrium
1st & 2nd Trimesters, Implantation, con’t.
a. Epithelium forms numerous glands
- may extend to myometrium
b. Cyclic changes controlled by hormones
- four phases
c. If implantation occurs, endometrium
is maintained in secretory phase
Implantation

Implantation begins ~ day 6






Trophoblast contacts
endometrium
Typically close to fallopian
tube
Trophoblast digests
endometrium
Enters “inner cell mass” first
Completed by ~day 11
** This concludes
“period of the ovum” **
1st & 2nd Trimesters, con’t.
V. Placenta & Fetal Membranes
A. Function of membranes:
1. house, protect, nourish
2. provide oxygen to
3. dispose of wastes for
embryo
1st & 2nd Trimesters, con’t.
B. Placenta
1. Decidua Capsularis:
a. After implantation, embryo covered
by endometrial layer
b. Maternal tissue
Placental formation

Decidua capsularis


Endometrial tissue
Covers implanting
embryo
1st & 2nd Trimesters, Placenta, con’t.
2. Decidua Basalis (Placentalis):
a. Endometrial layer between embryo
and myometrium
b. Maternal tissue that will be meshed
with fetal tissue
Placental formation

Decidua basalis



Between embryo and
mom
Gives rise to
maternal portion of
placenta
RNA virus DNA???
1st & 2nd Trimesters, Placenta, con’t.
3. Trophoblast develops a second layer
(chorion) during implantation
a. Inner layer sprouts villi
b. Villi penetrate decidua basalis
c. Maternal blood seeps into spaces
between villi
d. Forms “Chorion Frondosum”
Chorion Frondosum

Chorion frondosum


Chorionic villi
Maternal blood
1st & 2nd Trimesters, Placenta, con’t.
4. Placenta has two origins:
a. fetal portion: chorion frondosum
b. maternal portion: decidua basalis
5. Blood in placental vessels:
a. closely associated with maternal
blood
b. between chorionic villi
Formation of Umbilical Vessels

Placental vessels
contain fetal blood


Blood only
communicates with
mom’s blood via
diffusion
No direct mixing!
1st & 2nd Trimesters, con’t.
C. Fetal structures
1. Amnion
a. Inner fetal membrane
b. Produces amniotic fluid
c. Cushions embryo
d. Contains enzymes for
development
Fetal membranes

Amnion



Outer fetal
membrane
Folds around
embryo on all
sides
Forms amniotic
fluid
1st & 2nd Trimesters, Fetal structures, con’t.
2. Yolk Sac
a. Provides initial nourishment
-connects to fetal gut
b. develops from endoderm
c. produces first blood cells
d. forms part of primitive gut
e. gives rise to allantois
Fetal membranes

Yolk Sac



Formed from
endoderm
Minimal
nourishment
Provides
umbilical
vessels
1st & 2nd Trimesters, Fetal structures, con’t.
3. Umbilical Cord
a. Point of fetal/maternal
communication
b. Formed from amnion, yolk
sac, and body stalk
c. Allantois: Contributes
blood vessels to cord
** This concludes “period of embryo” (8 weeks) **
Umbilical Cord

Vessels arise from
yolk sac and forming
placenta



+O2 blood in
umbilical veins
- O2 blood in fetal
veins
+/- blood in fetal,
umbilical arteries
1st & 2nd Trimesters, con’t.
VI. Anomalies
A. Meckel’s Diverticulum of the Ileum p. 137
1. Persistence of proximal end
of yolk sac
2. Blind pouch
a. usually <10 cm
b. terminates at umbilicus
c. occurs in 2% of population
Meckel’s Diverticulum

Meckel’s
diverticulum of the
Ileum



May undergo torsion
May form fistulas
Sx mimic
appendicitis
1st & 2nd Trimesters, Anomalies, con’t.
B. Polyhydramnios
1. Volume of amniotic fluid > 2 liters
2. Associated with G.I. Tract
obstruction or atresia
3. Causes:
a. Diabetes Mellitus
b. Viral infection in utero
c. Rh incompatibility
1st & 2nd Trimesters, Anomalies, con’t.
C. Oligohydramnios
1. Volume of amniotic fluid < 1/3 liter
2. May cause amniotic “band”
syndrome
3. May be due to renal agenesis
1st & 2nd Trimesters, Anomalies, Oligohydramnios, con’t.
4. May indicate fetal demise, premature
rupture of membranes
5. Causes:
a. IUGR (Intrauterine Growth
Restriction)
b. Pulmonary Hypoplasia: lungs fail to
develop properly
1st & 2nd Trimesters, con’t.
A. Hydatidiform or Vesicular Mole
1. Occurs when embryo blights and
chorion persists
2. Associated with Theca Lutein cysts in
1/3 of cases
3. Chorionic villi transform into vesicles
4. Benign tumor, may become huge (molar
pregnancy)
1st & 2nd Trimesters, Anomalies, con’t.
E. Omphalocele
1. Results when intestines fail to retract
from umbilical cord
2. “Zipper” at linea alba fails to zip
3. External portion covered with skin of
abdomen
Omphalocele




Associated with various
trisomies and increased
AFP levels
Internal organs covered
with peritoneum and
amnion
Normal till 10 weeks
High fetal mortality rate
1st & 2nd Trimesters, Anomalies, con’t.
F. Ectopic Pregnancy
1. Implantation of embryo outside uterus
2. Ampulla is most common site
3. May implant on mesentery,
omentum, other sites
4. Rarely reach maturity
Ectopic Pregnancy


99% are tubal
pregnancies
Other sites:





Ovary
Mesentery
Cul-de-sac
Spleen
Liver
1st & 2nd Trimesters, Anomalies, con’t.
G. Metastatic Carcinomas
1. Spread via lymph circulation
a. Cervix: drains into internal
and external nodes
b. Body of uterus: drains into
superficial inguinal nodes
1st & 2nd Trimesters, Anomalies, con’t.
c. Fundus of uterus, fallopian
tubes, and ovary: drain
into para-aortic nodes at L-1
d. Vagina: drains into two directions
1st & 2nd Trimesters, Anomalies, con’t.
1. Lower 1/3 and vulva:
drain into superficial
inguinal nodes
2. Upper 2/3: drain to sacral,
external & internal iliac
nodes
2. Cancers may penetrate bladder or
rectum wall
1st & 2nd Trimesters, Anomalies, con’t.
H. Rectouterine Pouch (of Douglas) or
cul-de-sac
1. Lowest point in abdominal
cavity
2. Ectopic pregnancies, metastases
often found here
1st & 2nd Trimesters, Anomalies, con’t.
2. Collects excess fluid in peritoneal
cavity
a. May be drained via posterior fornix
b. Instruments may inadvertently
penetrate
1. Enter peritoneal cavity
2. May cause peritonitis
1st & 2nd Trimesters, Anomalies, con’t.
I. Hydrocephaly
1. Due to stenosis or blockage
a. cerebral aqueduct
b. foramina of Luschka or
Magendie
2. CSF cannot circulate
3. Collects in and expands ventricles
Hydrocephalus

Means “water in
the head”


Usually due to a
blockage in the
CSF circulatory
pattern
May be corrected
in utero
1st & 2nd Trimesters, Anomalies, Hydrocephalus, con’t.
4. Causes usually viral
a.
b.
c.
d.
e.
Toxoplasmosis (Valley Fever)
Rubella (3-day measles)
Treponema pallidum (syphilis)
Herpes virus infection
CMV infection (cytomegalovirus)
1st & 2nd Trimesters, con’t. Anomalies, continued …
J. Anencephaly:
1. Lack of cerebral hemispheres
2. Brainstem is intact
3. Basic functions are present
(breathing, heart beat)
1st & 2nd Trimesters, Anomalies, con’t.
K. Porencephaly
1. Cysts or cavities in cerebral
hemispheres
2. Cysts communicate with ventricles
1st & 2nd Trimesters, Anomalies, Porencephaly, con’t.
3. Hydranencepaly:
a. an extreme form
b. cerebral hemispheres
nearly absent
4. Developmental anomaly, or
ischemic infarction in utero
Doppler U/S of the Circle of Willis in utero
Circle of Willis
Fetal circle of Willis: 3D U/S
1st & 2nd Trimesters, Anomalies, con’t.
L. Spina Bifida
1. Defect of the spinal column
2. Due to failure of vertebral arches
to close
3. Meninges, neural tissue exposed
4. May be associated with severe
latex allergy
Ultrasound-guided Prenatal Diagnosis
Amniocentesis and CVS
1st & 2nd Trimesters, con’t.
VII. First Trimester Bleeding
A. Abortion (threatened or
spontaneous)
1. Distorted irregular gestational sac
2. Common during first pregnancy
a. Most women unaware
b. Up to 50% may abort
1st & 2nd Trimesters, First trimester bleeds, con’t.
B. Blighted ovum
1. embryonic membranes and
chorion develop
2. no gestational sac
C. Incomplete Abortion: embryo expelled,
POC retained
1st & 2nd Trimesters, con’t.
D. Molar gestation
1. Embryo blights
2. Chorionic villi become hydropic
3. Often accompanied by theca lutein
cysts
1st & 2nd Trimesters, con’t.
E. Ectopic pregnancy
1. Tubal implantation most common
2. Rupture results in bleeding
F. Pelvic masses
1. Uterine leiomyoma (fibroid)
2. Corpus luteum cysts
1st & 2nd Trimesters, con’t.
VIII. Uterine Anomalies:
- usually result from fusion abnormalities
of Mullerian ducts
- embryonic tubular structures that give
rise to fallopian tubes, uterus
A. Arcuate uterus: saddle-shaped
Uterine Anomalies
1st & 2nd Trimesters, Uterine anomalies, con’t.
B. Capped uterus: muscle of fundus is
contracted
C. Couvelaire uterus:
1. blood in myometrium
2. indication of placental abruption
D. Uterus acollis: uterus lacking a cervix
1st & 2nd Trimesters, Uterine anomalies, con’t.
E. Uterus bicornis (duplex uterus,
bifid uterus, uterus bifidis):
uterus divided in two
1. Uterus bicornis unicollis:
bifid uterus with one cervix
2. Uterus bicornis bicollis:
bifid uterus with two cervices
Uterine Anomalies, con’t…
Uterine Anomalies, con’t…
1st & 2nd Trimesters, Uterine anomalies, con’t.
F. Uterus biforis (uterus subseptus):
1. single uterine body
2. divided by short septum
G. Uterus bilocularis (septate uterus,
bipartite uterus, uterus septus):
- uterus is divided by a complete
anterior-to-posterior septum
Uterine Anomalies, con’t…
1st & 2nd Trimesters, Uterine anomalies, con’t.
H. Uterus didelphys: double uterus,
each with own cervix
I. Uterus incudiformis (uterus triangularis):
uterus bicornis with broad, flat fundus
J. Uterus parvicollis: normal uterus with
abnormally small cervix
K. Uterus unicornis: only one half of
the uterus exists
Uterine Anomalies, con’t…
Uterus didelphys
Uterus unicornis