Fetal growth,circulation &amniotic fluid 18

Fetal Growth Determinants of birth weight are multi-factorial &reflect the influence of the natural growth potential of fetus&the intrauterine environment which include maternal&placental factor. other factors are fetal hormones eg:insulin-like growth factor ,insulin,thyroxin& cortisol. Each baby has its own potential,wich can be preditable from physiological ccharacterstics at the beginning of pregnancy.

Physiological variables affecting normal fetal growth -pre pregnancy weight & maternal booking weight - maternal height -maternal age& parity - ethnic group -fetal sex -paternal height

Cardiovascular system The fetal circulation is different from adult. 3 modifications in fetal vascularity ensures that best,oxygenated blood from the placenta is delivered to the fetal brain, these are: 1.ductus venosus 2.foramen ovale 3.ductus arteriosus

Circulation Oxygenated blood passes from the placenta to the fetus through the umbilical vein which divides into 2 branches ,one that supplies the portal vein in the liver ,&another narrow vessel ,ductus venosus, which joins inferior vena cava. Blood stream passes across right atrium through a physiological defect in atrial septum,FORAMEN OVALE to left atrium ;then to left ventricle to aorta .by this only small portion of blood pass to the lungs why?

circulation nearly 1/3 of the blood flow through the ductus arteriosus pass to the body , and the other 2/3 is passed to the placenta through the2 Hypogastric arteries (distally become the umbilical artery) then the blood comes back from the placenta by the umbilical vein.

circulation Prior to birth ,the ductus remains patent by the vasodilator prostaglandin E2 &I .premature closure occure by the use of cyclo-oxygenase inhibitors like? At birth cessation of umblical blood flow causes cessation of flow in the ductus venosus ,a fall in pressure in right atrium &closure of foramen ovale

ciculation At birth ventilation of the lung opens the pulmonary circulation, with a rapid fall in pulmonary vascular resistance .The ductus arteriosus functionally closes within few days of birth.

Circulatory changes after birth The hypogastric artery (umbilical artery) will be atrophied and obliterated forming the umbilical ligaments. Intra-abdominal remnant of the umbilical vein form the ligamentum teres. Ductus venosus constrict by 10-96hours after birth, anatomically become closed by 2-3weeks(ligamentum venosum).

Respiratory system LUNG Full defferentiation of capillary canalicular elements of lung is by 20 weeks .aleoli develop after 24 w. Fetal breathing movements occur in utero &inceases with gestational age Does fetal lung inspire highly oxygenated or low oxygenated air ??

surfactant Is a phospholipid consist mainly from lecithin (80%) &its production enhanced by cortisol,growth restriction&prolonged rupture of membrane and delayed in diabetic patient .other phospholipid may be more potent in redusing surface tention e g phosphotidylglycerol wich is predictive in diabetic mother?

Normal lung development Requires adequate liquor &respiratory movement .oligohydramnios, decreased intrathoracic space ,chest wall deformities result in pulmonary hypoplasia which lead progressive respiratory failure Respiratory distress syndrome(RDS) is specific to prematures & associated with surfactant deficiency

Fetal blood The first fetal blood cells are formed on the surface of the yolk sac from 14_19 day until the third month. During the fifth week extramedullary hemopoesis begin in the liver & spleen then bone marrow at 7-8 weeks to become the predominant Most hemoglobine is fetal (HbF) which has two gama chain(alfa 2-gama 2) which have higher affinity to oxygen.from28-34 w ,a swich to HbA occures & at term HbF \HbA is80:20.

Fetal behaviour Fetal movement can be first perceived by the mother by 18w in primiparae &several weeks earlier in multiparae Diminished fetal movement associated with chronic hypoxia,growth failure, &may be precursor of fetal death With maturation of CNS the fetus developed well defined behavioural states

AMNIOTIC FLUID By 12w the amnion comes in contact with inner surface of the chorion &obliterates the extra-embryonic coelom to become adherent but not fused both lack vessels or nerves but contain phospholipid&enzymes Choriodecidual function play important role in the initiation of labour by the production of E2&F2a

Source of amniotic fluid Initially secreted by amnion but by 10 w it is transudation from fetal serum via skin &umbilical cord thenfrom16w the increase amount from imbalance between lung &kidney contribution &between swallowing. The volume increases 30ml in 10w to 1000ml in 38w then decreases.

Amniotic fluid At term the specific gravity of the fluid is 1010. It contains 99%water and it’s less osmolality than the maternal and fetal plasma. It has organic, inorganic and cellular constituents. Some concentration of important contents near term are: sodium 130mmol/l urea 3-4mmol/l protein 3 g/l lecithin 30-100mg/l alpha-fetoprotein 0.5-5 mg /l

Function protection ,prevention ,movement &development, The forewater bag form a wedge which with uterine contraction dilates the internal os and the cervical canal. At the rupture of the membrane during labour the fluid flushes the lower genital tract( aseptic and bactericidal). The amnion produce a variety of bioactive compounds including vasoactive peptides, growth factors, and cytokines.

Disposal of the amniotic fluid It’s partly by the absorption through the amnion in to maternal plasma and partly fetal swallowing and absorption by the fetal intestine to enter the fetal plasma.

Investigation of the amniotic fluid Samples of amniotic fluid can be obtained during pregnancy for various diagnostic purposes by abdominal amniocentesis, and a variety of chemical estimations for normal and pathological constituents can be made. Fetal amniotic cells can be obtained for tissue culture and chromosomal study.