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Fetal Period
SOHRABI
/ /۲۰۲۳ ۰۴ ۲۱ :۰۸ ۴۵
Beginning of 3rd month to
end of pregnancy
Fetal
period
Supportive Structures
• Certain structures develop to support, maintain, new life throughout pregnancy– Embryonic or fetal membrane (chorion and
amnion)– Placenta– Umbilical cord
Amnion
Envelop the embryo and
umbilical cord.
Umbilical Cord
Umbilical Cord• Lifeline between placenta and fetus• Contains 3 vessels
– 2 umbilical arteries– 1umbilical vein
• Wharton’s jelly– Gelatinous material surrounding cord– Prevents cord from collapsing, kinking
• 18-20 inches long
8th week30 mm
amniotic sac
umbilical cord
placenta
Amniotic fluid
• Amniotic fluid contains– Fetal urine– Fetal hair– Sabaceous materials– Epithelial cells– Clear fluid /98% water
• Functions– Prevents amnion from sticking to embryo– Allows movement of embryo– Maintains constant normal body temp. for
embryo– Helps to protect fetus from outside injury– Provides nourishment (can drink up to …
daily)
Amniotic fluid initially is isotonic, but as fetus develops; concentration changes by urine and sloughed cells of the fetus, placenta, and amniotic sac.
– Contains 500-1000ml of amniotic fluid
– Oligohydramnios: < 500 ml• Causes associated with oligohydramios
– Fetal genitourinary anomalies– Uteroplacental insufficiency– Fetal hypoxia
– Polyhydramnios: > 2000ml at birth• Factors associated with polyhydramnios
– Spinal bifida– Anencephaly– Diabetes
Amniotic sac at term
What is a placenta?
Temporary structure
Functions as an organ and endocrine gland
Is shared by embryo and the woman
Fully functional by the 12th week of pregnancy
The FetusWeek 16
The Fetus
Week 8
How is the placenta formed?
– Outermost layer of “bag of waters” is chorion
– Finger-like projections from chorion form chorionic villi
– Chorionic villi embed within the decidua forming the placenta
Placenta• Syncytiotrophoblast secretes
enzymes that create blood filled cavities in the maternal tissue.
• Cytotrophoblast then forms villi that grow into the pools of venous blood.– Produces chorion
frondosum on the side that faces the uterine wall.
• Other side of chorion bulges into the uterine cavity(chorion laeve).
Placenta
• Decidual reaction:– Endometrial growth.– Accumulation of glycogen.
• Decidua basalis: – Maternal tissue in contact with the
chorion frondosum.
• Decidua basalis and chorion fondosum together become placenta.
Circulation is the result of a decidual reaction
– Stromal cells of the endometrium enlarge
– Capillaries become dilated and form sinusoids
– Erosion of these sinusoids by the trophoblast fills area with maternal blood establishing a primitive circulatory system
Maternal circulation in the placenta is outside of the maternal circulator
system
Placental circulation
Maternal blood flows into spaces between villi (intervillous spaces)
Returns fetal waste products to maternal circulation
Maternal and fetal blood does not mix unless there is a rupture of the chorionic
villus
Size & shape
of
placenta
Fetal surface
Maternal surface
Placenta Perevia
Placenta Function
– Transfer of oxygen and nutrients to fetus– Removes fetal waste
– Protects fetus by transferring maternal antibodies to fetus
• Synthesis of hormones to maintain pregnancy (endocrine gland)– Estrogen– Progesterone– Human chorionic gonadotropin (HCG)– Human placental lactogen(HPL)– Relaxin
Progesterone– Aids in development of
the decidua– Progesterone Decreases
uterine contractility– Promotes fat storage to
prevent starvation– Decreases GI motility and
bladder/ureter toneStimulates uterine growth.
– Suppresses LH and FSH.– Stimulates development
of alveolar tissue of the mammary gland.
EstrogenPromotes growth and enlargement of fetusEndometrial growth.Promotes maternal vascularitystimulates ductal development in breastCauses pigmentation changesInhibition of prolactin secretion.Enlargement of mother’s uterus.
Placental hormones
• HCG– Stimulates the corpus luteum to release
estrogen/progesterone until placenta is functional
Stimulates male fetus to release testosterone /aids in intrauterine development of male reproductive tract
– Responsible for positive home pregnancy test
– Prevents immunological rejection of implanting embryo.
– Has thyroid-stimulating ability.– Produces effects similar to LH.
HPL (human placental lactogen)Promotes maternal changes in metabolism (increased to meet needs of growing fetus)Contributes to breast enlargement
RelaxinPromotes relaxation of sacroiliac, sacroccygeal, and pubic jointsPrevents premature labor contractionsPromotes cervical softening
Placental hormones
Placental hormones
• crown-rump length (CRL) (sitting height)
• crown-heel length (CHL), the measurementfrom the vertex of the skull to the heel
(standing height)
• Length(3,4,5 months)• Weigh 5 month= 500 gr.• Weight(8,9 months) ,3600 gr.
Age(Weeks)CRL(Cm)Weight(gr)
9-125-810-45
13-169-1460-200
17-2015-19250-450
21-2420-23500-820
25-2824-27900-1300
29-3228-301400-2100
33-3631-342200-2900
37-3835-363300-3400
• Ultrasond:• 4th-7th weeks, CHL• 16th -30th weeks, BPD,…
• In general, the length of pregnancy is considered to be:• 266 days or 38 weeks after fertilization
• 280 days, or 40 weeks after the onset of the last normal menstrual period(LNMP)
50 mm
9 weeksToes separate eyelids develop major parts ofbrain are present
61 mm
10 weeksChin grows nostrilsseparate face appearshuman genitals appearmale or female
11 weeksWell-defined neck appearinggenitalia arecompleting sucking reflex appearing
73 mm
87 mm
12 weeksWell-defined neck appearsFingers/toes formedNail beds begin formationTooth buds present Placenta totally formed and functioningFHT audible with doppler
12 weekssucking reflex appearsGenitalia are complete
3rd Month
• Position of eyes and ears• Position of limbs• Primary ossification centers• Return of physiological hernia• Sex definition• Nervous reflexes
140 mm
16 weeksall major organs form
Blood cells form
Palate and nasal septum closure
Swallows amniotic fluid and excretes urine
Head hair & Lanugo(body hair)
forms over body
movements are felt by mother
20 weeksQuickening (fetal movement) by primipara
Considered the age of viability because some infants have survived at this age
5th Month
• Lanugo hair on body• Hair of head and eyebrows• Sense of fetus movement by mother
230 mm
24 weeksSkin is wrinkled fat depositing under skin(Subcutaneous fat )
Eyebrows and eye lashes are formed
pupils react to light
Lung alveoli maturation & lung circulation develop
270 mm
28 weeksFetus may be viable if born eyelids openVernix caseosa protects skin
6th , 7th Month
• 25 Cm, 1100 gr.• Red and shrink skin
300 mm
32 weeksmostsenses are well developed
fat deposits increase
body hair is lost but head hair is well developed
Fingerprint formation
Areola of breast visible but flat
Skin is pink
Vigorous fetal movement
36 weeks Lanugo is
disappearing Breast tissue
further develops Body begins to
look plump and rounded
fetus turning head downin uterus
350 mm
40 weeksInfant is full-term
Skin is smooth; lanugo is gone from face and extremties
Fingernails are fully formed and extend to ends of fingers
Eye color is established
Head erect
8th, 9th Month
• Vernix caseosa• 3600 gr.• CRH=36 Cm• CHL=50 Cm
Birth
• Premature• Postmature
IUGRIntrauterine Growth Restriction
SGASmall for Gestational Age
Fetally MalnourishedDysmature
IUGR
10%With:neurological deficienciescongenital malformations
meconium aspirationHypoglycemiaHypocalcemiRespiratory distress syndrome (RDS).higher in blacks than in whites
Causative factors: • chromosomal abnormalities (10%)• teratogens• congenital infections (rubella,• cytomegalovirus, toxoplasmosis, and syphilis)• poor maternal health (hypertension and renal and cardiac disease the mother’s nutritional status and socioeconomic level; her use of cigarettes, alcohol, and other
drugs• placental insufficiency; and multiple births (e.g., twins, triplets
• The major growth-promoting factor during development before and after
birth is insulinlike growth factor-I (IGF-I), which has mitogenic and
anabolic effects.
• Fetal tissues express IGF-I and serum levels are correlated with fetal growth.
• Mutations in the IGF-I gene result in IUGR and this growth retardation is continued after birth.
• In contrast to the prenatal period, postnatal growth depends upon growth hormone (GH). • This hormone binds to its receptor (GHR), activating a signal transduction pathway and resulting in
synthesis and secretion of IGF-I. • Mutations in the GHR result in Laron dwarfism, which is
characterized by growth retardation, midfacial hypoplasia, blue sclera, and
limited elbow extension.• These individuals show little or no IUGR, since IGF-I production does not depend upon GH during fetal development.
The End