Fetal circulation

1. Oxygenated blood enters fetus from placenta via umbilical vein
2. Blood enters IVC
   • 50% directly through liver/hepatic sinusoids
   • 50% via ductus venosus (later ligamentum venous in ligamentum teres)
3. From IVC blood enters right atrium
   • Passes through foramen ovale into left atrium, mixes with blood returning from lungs, ejected into left ventricle
   • Passes into right ventricle, to pulmonary trunk then aorta via ductus arterious (later ligamentum arteriosus)
4. Blood enters the aorta
5. Half of blood enters umbilical arteries (medial umbilical ligament) for return back to placenta

Circulatory changes at birth

1. Shunt closure
   • FO closes (pressure effect)
   • DV closes
   • DA closes -
2. Fall in pulmonary vascular resistance
   • Following airation of lungs
   • Rise in pulmonary blood flow
3. Closure of umbilical vessels