Fetal Development: Dr. Dina Nawfal Dr. Dina Nawfal Department of Obstetrics & Gynecology College of Medicine University of Mosul

Fetal Development Fetal Development: fetal growth is dependent on  adequate transfer of the nutrients and oxygen across the placenta (maternal nutrition and placental perfusion).  hormonal effects also play an important role of fetal growth like insulin and thyroxin.

Cardiovascular system and fetal circulation:  fetal circulation is quite different from that of the adult  characterized by four shunts 1- Umbilical circulation.

2- Ductus venosus.

3-Foramen ovale

4- Ductus arteriosus

 The umbilical vein, carrying oxygenated blood from the placenta to the fetal body enters the portal system  most of the blood bypass the liver through ductus venosus which directly enters the inferior vena cava  blood reaching the heart through the inferior vena cava has an O2 saturation of about 70%.

 one-third of blood returning to the heart from inferior vena cava flows across the right atrium through the foramen ovale to the left atrium  blood flows from the left atrium into the left ventricle and then to the ascending aorta to supply the brain and upper body  most of the blood that enters right atrium enters the right ventricle

 the descending aorta supplies the lower body and the major portion of blood flow goes to the umbilical arteries which carry deoxygenated blood to the placenta  right ventricular outflow enters the pulmonary artery and the blood will bypass the lungs and flow through the ductus arteriosus to the descending aorta

Changes in the fetal circulation after birth  Shortly after birth the umbilical vessels,ductus venosus, foramen ovali and ductus arteriosus are obliterated.  Absence of placental circulation.  lung expansion.  Reduce pulmonary vascular resistance.  the right and the left ventricle work in series.

Factors increasing the oxygen supply to the fetus 1- Increase diffusion of oxygen across the placenta. 2- High hemoglobin(Hb) concentration. 3- Presence of Hb F which has high affinity to oxygen.

Respiratory system The lung first appears as an outgrowth from the primitive foregut at about 3-4 weeks.

By 20 weeks the conductive airway tree and parallel vascular tree is well developed.

 Surfactant production starts from about 30 weeks & act by lowering surface tension of the alveoli & prevent its collapse.  inadequate amounts of surfactant result in (RDS).  fetal breathing movements occur in utero  Adequate amniotic fluid volume is necessary for lung maturation

Gastrointestinal system The primitive gut is present by the end of the 4th week and consists of three parts, the foregut, midgut and hindgut.

 Peristalsis in the intestine occurs from the second trimester  at term the large bowel is filled with meconium  meconium aspiration syndrome and respiratory distress can occur if meconium aspirated in utero.

Liver, pancress and gall bladder  The pancreas, liver and epithelia lining of the biliary tree derive from the endoderm of the foregut  By the sixth week, the liver performs haematopoiesis  Due to reduced ability to conjugate bilirubin, physiological jaundice are common after delivery  Glycogen is stored within the liver, maximal in the third trimester

Kidney and urinary tract The kidney, recognized in its permanent final form (metanephric kidney) by 4 th weeks

 The mesoderm in the thoracolumbar area become epithelial tubules  The excretory and the collecting system are completed by the weeks of gestation but these structures are not yet mature and the maturation and concentration ability is gradual and continues after birth

Blood and immune system  Very early red blood cells and immune cells are derived from haematopoietic cells in the yolk sac.  By 8 weeks the yolk sac is replaced by the liver as the source of these cells  By 20 weeks almost all of these cells are produced by the bone marrow.  Immunoglobuline G (IgG) originates mostly from the maternal circulation  Maternal IgM and IgA are not cross the placenta

 Ninety per cent of fetal haemoglobin is HbF between 10 and 28 weeks gestation.  At term the ratio of HbF to HbA is 80:20  HbF has a higher affinity for oxygen than HbA  At birth, the mean capillary haemoglobin is 18 g/dl

Endocrine system Major components of the hypothalamic-pituitary axis are in place by 12 weeks gestation. thyroid gland produces thyroxine from (10 to 12)weeks Behavioral status first activity is the beating of the fetal heart 5-6 weeks followed by fetal movements at 7-8 weeks. by 12 weeks breathing movement, yawning, sucking and swallowing.

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