Physiology of pregnancy.
The perinatal care of the fetus.
Prepared by N. Bahniy
STAGES OF PRENATAL
DEVELOPMENT
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Preembryonic stage - first 2
weeks.
Products
of
conception are called as
conceptus.
Embryonic stage - from the
third week until the end of
the eight week. From this
period conceptus is called
embryo.
Fetal period starts from the
beginning of the ninth week
through the full 41 weeks of
development. Products of
conception are called as
fetus.
Preembryonic Stage
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fertilization
zygote formation
division of fertilized ovum
morula formatiom
formation of free blastocyst
implantation of the ovum in
the uterine wall
Primitive
chorionic
villi
formation
Initial folding into layers –
gastrulation beginning.
Chorion and amnion begin
to form during this period
also.
A SPERM FERTILIZING AN OVUM
Formation of free blastocyst
Morula
From inner layer embryoblast
From outer layer trophoblast
Implantation- attachment of the
blastocyst on the 7th day into uterine wall
called implantation.
EMBRYONIC STAGE

Formation of supportive structures - include the placenta, umbilical
cord, and certain extraembryonic membranes.
 The yolk sac forms early and manufactures blood cells until the liver
takes over at 6 week.
 The allantois forms the part of the yolk sac; it produces blood cells and
eventually forms the umbilical arteries and veins.
 During the third week the primitive streak appears, and then, other
rudiments of organs form, including the central nervous system,
notochord, neural tube, heart, limbs, finger, toes, eyes, ears, and nose.
AN AMBRYO IS ABOUT 5 WEEKS OLD
"FETUS OF ABOUT EIGHT WEEKS, ENCLOSED IN THE AMNION,"
FROM GRAY'S ANATOMY. PART OF THE PLACENTA IS SHOWN AS THE
LOWEST FEATURE IN THIS IMAGE, AND THE AMNION EXTENDS
1
ABOVE THE FETUS.[
Critical periods of fetal
development
 Implantation
 Morphogenesis
 Placentation
and organogenesis
Growing and differentiation of the
structures during the Fetal Period
Conceptus structure in the end of
pregnancy
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Fetus
Umbilical cord
Placenta
Amniotic Fluid
Amnion
Chorion
Decidua
Fetal characteristics
Classification
“Deep
pre-term
fetus”
Gestational age
(weeks of
pregnancy
Weight, gram
Length, cm
Signs of maturity
12 – 22
25 – 500
9 - 25
Absent
500 – 2500
25 - 46
Absent
“Fetus pre-term”
22 –36+6 days
“Fetus in-term”
37 – 41
> 2500
(3200-3500)
47
(50-52)
Present
> 41
> 2500
47
Present
“Fetus post-term”
Signs of fetal maturity
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Umbilical ring is between pubis and
processes xyphoideus
Pink skin
Well-developed subcutaneous tissue,
Lanugo in the shoulders and upper part
of the back
Length of the hair on the head is 2 cm
Nails are present till the top of the fingers
Well-developed ears and nose cartilage
Testes are present in the scrotum in the
boys and labia major are covered labia
minor in the girls
Active movements
Loud cry of the infant
FETAL HEAD AT TERM
DIAMETERS OF THE FETAL HEAD
AT TERM
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1. The suboccipitobregmatic (9.5 cm, 32cm),
which follows from the middle of the large
fontanel to the undersurface of the occipital
bone.
2. The suboccipitofrontalis (10cm,33 cm) –
from subocipital fossa to border of the hair.
3. The occipitofrontal (12 cm, 34 cm), which
follows a line extending from a point just
above the root of the nose to the most
prominent portion of the occipital bone.
4. The occipitomental (12.5-13 cm, 3941cm), from the chin to the most prominent
portion of the occiput.
5.The sublingquobregmatica (9,5 cm, 32
cm).
6. The biparietal (9.5 cm), the greatest
transverse diameter of the head, which
extends from one parietal boss to the other.
7. The bitemporal (8.0 cm), the greatest
distance between the two temporal sutures.
DIAMETERS OF THE FETAL BODY
AT TERM

Biacromial distance
– 12cm, 34-35 cm
 Bisiliacus distance –
9cm, 27-28 cm
DECIDUA - MATERNAL MEMBRANE,
immunologically specialized tissue.
provides for embryo-fetal nutrition.
Fetal membranes

Structure
chorion and amnion
 Amnion
A double-layered
translucent membrane
Become distended
with fluid
Amniotic fluid 1000-1500ml at 36th38th week (peak) Absorb
1.
2.
3.
4.
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1.
2.
3.
Fetal membrane
Umbilical cord
Fetal skin
Fetal drinking
Source
Fetal urine
Fetal lung
Exudation of amnion
and fetal skin
Functions:
Protection of the fetus
Protect mother, prevent
infection
Formation of the forebag
Umbilical Cord

Structure
amnion, yolk sac,
one vein, two artery
and Wharton jelly
 Length
30-70cm
Placenta at section

Fetal and maternal
parts.
 Cotyledon –
is a small
compound of placenta.
Placental villi

At term, the placenta
contains
approximately 12 m2
of villous surface area
for
maternofetal
exchange.
Placental functions

Endocrine
 Transfer of nutrients
 Excretory - removal
of the products of
fetal catabolism
 Barrier
 Oxygen-transport
Placental hormones
1. Protein hormones of the placenta:
chorionic gonadotropin (cHG)– it is maintain the function of the corpus
luteum during early gestation, promote uterine vascular vasodilation
and myometrial smooth muscle relaxation, relaxin secretion by the
corpus luteum, stimulate thyroid activity, and some more basic forms
also stimulate iodine uptake
human lactogen – its actions include lipolisis and an increase in the
levels of circulating free fatty acids, thus providing a source of
energy for maternal metabolism and fetal nutrition
2. Steroid hormones of the placenta: estrogens; progesterone.
3. Chorionic adrenocorticotropin and thyrotropin, growth hormone
variant, parathyroid hormone-related protein (PTH-rP), calcitonin,
and relaxin – no significant role has been established for this
substance in normal human pregnancy.
4. Hypothalamic-like-releasing hormones of the placenta
Type of human placentation -
hemochorioendothelial
Role of Estrogen in Pregnancy:
Increasing blood flow to the uterus by
promoting vasodilation.
 Changing the sensitivity of the
respiratory system to carbon dioxide.
 Softening of the cervix, initiating uterine
activity, and maintaining labor.
 Developing the breasts in preparation
for lactation and secretion of prolactin
by the pituitary gland.
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Role of Progesterone in
Pregnancy:

Ready the uterus for implantation.
 Relaxes smooth muscle to prevent
spontaneous abortion.
 Works to prevent a maternal immunologic
response to the fetus.
 Relaxes smooth muscle
– to decrease motility & improve absorption of
nutrients.
– Enlarges the ureters & bladder to increase
capacity.
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Plays a role in development of the alveoli &
ductal system to prepare for lactation.
Physiologic changes in
pregnant woman
Genital organs
1.
Uterus
1)
capacity: 5ml-5000ml.weight: 50g1000g
2)
Hypertrophy of muscle cells
3)
Endometrium→decidua: basal
decidua, capsular decidua, true
decidua
4)
Contraction: Braxton Hicks
5)
Isthmus uteri: 1cm→ 7-10cm
6)
Cervix: colored
7)
Ovary: placenta replaces ovary
(10th week)
8)
Vagina: dilated and soft, pH↓(antibacteria)
9)
Ligaments: relaxed
Physiologic changes in
pregnant woman
Cardiovascular system
1. Heart:
move upward, hypertrophy of cardiac
muscle
2. Cardiac Output
increase by 30%, reach to peak at 32nd –
34th week
3. Blood pressure
early or mid pregnancy Bp↓.late
pregnancy Bp↑ .Supine hypotensive
syndrome
Physiologic changes in pregnant woman
Hematology
1. Blood volume
1) Increase by 30%-45% at 32nd –34th (peak)
2) Relatively diluted
2. Composition
1) Red cells
Hb:130→110g/L, HCT:38%→ 31%.
2) White cells: slightly increase
3) Coagulating power of blood: ↑
4) Albumin: ↓,35 g/L
Physiologic changes in pregnant woman
The Respiratory system
1. R rate: slightly ↑
2. vital capacity: no
change
3. Tidal volume: ↑ 40%
4. Functional residual
capacity:↓
5. O2 consumption: ↑
20%
Physiologic changes in pregnant
woman
Kidney
1) Renal plasma flow
(RFP):↑35%
2) Glomerular filtration
rate (GFR):↑ 50%
2. Ureter
Dilated (P↑)
3. Bladder
Frequent urination
1.
Physiologic changes in pregnant woman
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Gastrointestinal
system
1) Gastric emptying
time is prolonged→
nausea.
2) The motility of large
bowel is diminished
→ constipation
3) Liver function:
unchanged
Physiologic changes in pregnant woman
Endocrine
1. Pituitary (hypertrophy)
1) LH/FSH: ↓
2) PRL:↑
3) TSH and ACTH:↑
2. Thyroid
1) enlarged (TSH and HCG↑)
2) thyroxine↑ and TBG↑ → free T3 T4
unchanged