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