Blood is supplied from the placenta to the baby via the umbilical vein.

Ductus venosus is a foetal blood vessels that connect the umbilical vein to the IVC.  Carries highly oxygenated blood from the placenta to the foetus

Foramen ovale & caval valve - the umbilical cord delivers oxygen rich blood to the baby’s atrium, most of this blood travels through the foramen ovale into the LA and is directed by the caval valve.  This is to bypassing the pulmonary circulation since the foetal lungs do not contain air

allows oxygenated blood from umbilical cord to pass from RA to LA, directed by caval valve. allows bypassing of pulmonary circulation as foetal lungs dont contain air. at birth a sudden drop in RA pressure assosiated with increased LA pressure closes the caval valve which fuses and becomes the fossa ovale. ~25% have incomplete closure, often asymptomatic.

Ductus arteriosus - Protects the lungs against circulatory overload and carries medium oxygenated blood (mixed with venous blood) from pulmonary trunk to aorta, thereby bypassing the pulmonary circulation

immediately after birth, ductus arteriosus constricts, allowing the blood from the RV to enter pulmonary arteries

collapsed lungs contribute high resistance to pulm flow

reliance on placenta for gas exchange

blood shunts from RA to LA through foramen ovale

blood shunts from pulm artery to aorta through ductus arteriosus (kept open by PGE1/PGE2)

lungs inflate, drop in pulmonary resistance and decrease R side pressure

removal of placental circulation increases systemic resistance increasing LA/LV pressure leading to foramen ovale closure within 6 months

increased oxygenation status inhibits PGE1/PGE2 release and allows ductus arteriosus SMC to contract, completly closing within 72 hours