Fetal and neonatal circulation

The fetal circulation is designed to serve prenatal needs. Very little blood goes to the lungs before birth because they are nonfunctional.
The well-oxygenated blood returns from the placenta into the umbilical vein, goes through the ductus venosus and vena cava inferior (which also receives deoxygenated blood from the portal vein) to the right atrium. Most of the blood goes through the foramen ovale into the left atrium and mixes with the blood from the pulmonary veins. The blood passes into the left ventricle and leaves via the ascending aorta.
A small amount of blood goes from the right atrium into the right ventricle, leaves by the pulmonary trunk and through the ductus arteriosus into the aorta. The mixed blood from the descending aorta returns to the placenta through umbilical arteries.

Circulation before birth

1. Liver
2. Portal vein
3. Umbilical vein
4. Ductus venosus
5. Right atrium
6. Right ventricle
7. Vena cava superior
8. Foramen ovale
9. Vena cava inferior
10. Left atrium
11. Left ventricle
12. Ductus arteriosus
13. Lung
14. Pulmonary vein
15. Pulmonary artery
16. Descending aorta
17. Umbilical arteries
18. Ascending aorta
19. Interventricular septum
20. Ventricural wall

At birth, the circulation of the fetal blood through the placenta ceases and the lungs begin to function.
The foramen ovale, ductus arteriosus, ductus venosus and umbilical vessels subsequently close or transform into corresponding ligaments.

Circulation after birth

1. Vena cava inferior
2. Liver
3. Portal vein
4. Ligamentum teres hepatis
5. Lung
6. Pulmonary vein
7. Pulmonary artery
8. Vena cava superior
9. Ligamentum arteriosum
10. Closed oval foramen
11. Descending aorta
12. Medial umbilical ligament
13. Superior vesical artery
14. Ascending aorta
15. Interventricular septum
16. Ventricural wall