Download Fetal Physiology

Fetal Physiology
Jennifer McDonald DO
Fertilization

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
300 million sperm
deposited in the
vagina
300,000 reach the
upper vagina &
uterus
300 make it to the
fallopian tube
 1 will be able to
fertilize egg
MORULA
The zygote undergoes rapid cell division without
cell growth (termed cleavage) until a solid ball of
cells is produced termed the morula. The cells
that make up the morula are termed blastomeres.
16 cells/4 days post-fertilization
BLASTULA
The center of the morula “hollows out” and creates
blastula. The space inside the blastula is termed
the blastocele.
Blastocyst begins developing two
cell types:
Embyroblast = inner cell mass
Trophoblast
Implantation 5-6 days postovulation
hCG secreted by trophoblast
GASTRULA
Cell migration results in the formation
of the gastrula. The gastrula contains
three layers of cells termed germ layers.
13 days post-fertilization
Ectoderm - Cells of the ectoderm will form the outer skin &
nervous system
Endoderm - Cells of the endoderm form the digestive tract and
& associated organs.
Mesoderm - Cells of the mesoderm give rise to muscle, connective
tissues, & reproductive tissues.
Visible Embryo www.visembryo.com
Placenta

Greek “plakous” = flat cake
Origins
Maternal = decidua basalis
Fetal = chorion frondosum
Placental Functions
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Respiratory function
Nutritive function
Excretory function
Production of enzymes
Production of pregnancy associated
plasma proteins (PAPP)
Barrier function
Endocrine function
Respiratory Function

O2 and CO2 cross the placenta by simple
diffusion
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Fetal hemoglobin has a higher affinity
and carrying capacity for oxygen than
adult hemoglobin
Nutritive Function
Simple diffusion
Active
transport
Facilitated
diffusion
Pinocytosis
Excretory Function

Waste products as urea passed from
fetus through placenta via simple
diffusion
Barrier Function
Maternal blood (intervillous spaces) &
fetal blood (chorionic villi) remain
separated by the Placental Barrier

Endothelium of fetal blood vessels
 Villous stroma
 Cytotrophoblast
 Syncytioptrophoblast
Incomplete Barrier
Does allow passage of antibodies,
hormones, many drugs, some viruses


Large molecular size molecules do not
cross (eg insulin, heparin)
Hormone Function - hCG
Human chorionic gonadotropin
 Produced by the synciotrophoblast
 Rises sharply after implantation peaking
10-12 weeks of pregnancy
 Detectable 9 days after mid-cycle LH
peak
 Doubling time 1.3-2 days

Human Placental Lactogen (hPL)
Produced by synciotrophoblast
 Similar to growth hormone
 Increases free fatty acids providing
sources of nutrition
 Inhibits gluconeogenesis
 Mammotrophic & lactogenic effect

Estrogen & Progesterone

Estriol is the major pregnancy estrogen
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Progesterone is synthesized in the
synciotrophoblast from maternal
cholesterol
Multiple gestations
Twins
1:80
Triplets 1:6400
Quadruplets etc.
1:512,000
Twinning
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Dizygotic (70%)
Separately fertilized ova
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Does have hereditary pattern
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75% time same sex
 Race is a factor (AA most common)
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10 fold increase in women with previous set of twins
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Rate increases with increasing age (peak 35-40)
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More common in women who become pregnant soon
after stopping oral contraceptives
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Twinning
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Monozygotic (30%)
Types
di/di = Separation before differentiation of the
trophoblast (before Day 3)
 mono/di = After trophoblast but before amnion
formation (Days 3-8)
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mono/mono = After amnion formation (Days 8-13)
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Conjoined twins = Days 13-15

Placental Abnormalities
Amniotic Bands
• Tear of amnion early in development
• Constriction bands
• Other associated anomalies club foot, syndactyly,
facial abnormalities
Twin Twin Transfusion Syndrome
• Can only happen in
monochorionic gestations
• Abnormal vessel
communications deep
within the placenta
• Donor Twin
• Recipient Twin
Placenta Previa
Implantation of the placenta
over the cervical os

Commonly seen in second
trimester
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Marginal previa = 2 to 3 cm
from os
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Increased risk for bleeding

Cesarean delivery
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Increased risk for placenta
accreta
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Placenta Accreta
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Abnormal trophoblast invasion into the
myometrium
Associated with life threatening
hemorrhage and increased need for
immediate hysterectomy
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Placenta Increta/Percreta
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Increta = invasion deep into myometrium
 Percreta = invasion through the serosa
into surrounding tissues
 Life threatening
 Placenta often left in place
Risk Factors
Advanced maternal age
 Increased parity
 Prior uterine surgery
Highest risk for accreta is having had
previous c-section for previa
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24% (one)
67% (four or more)
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Umbilical Cord
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Develops from the connecting stalk
 At term measures about 50 cm
 2 cm diameter
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Long cord > 100 cm
Short cord < 30 cm
Structure: It consists of mesodermal
connective tissue called Wharton's jelly,
covered by amnion.
It contains:

One umbilical vein carries oxygenated
blood from the placenta to the foetus

Two umbilical arteries carry
deoxygenated blood from the foetus to
the placenta,
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Remnants of the yolk sac and allantois.
Abnormalities of the Umbilical Cord
Velamentous
Insertion
• Vessels divide before
reaching chorionic plate
• 1% of placentas
• 25-50% infants
structural defects
Vasa previa = vessels present ahead of the fetus
Cord Lengths
Short Cord
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Less than 30 cm
Early separation
Delayed descent
Uterine inversion
Long Cord
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More than 100 cm
 Cord prolapse
 True knots
Coiling around the
neck
Knots
False Knot
Localized collection of Wharton’s jelly
containing a loop of vessels
True Knot
Fetus passes through a loop of cord
If pulled tight can result in asphyxia
Single Umbilical Artery

May be associated with congenital
anomalies (30%)
 Occurs one in 500 deliveries