Fetal circulation is different from postnatal (adult) circulation to accommodate the unique environment of the womb. Here’s an overview of fetal circulation:

1. Oxygen and Nutrient Supply: The fetus relies on the mother’s bloodstream for oxygen and nutrient supply. Oxygen-rich blood from the mother flows through the placenta and into the umbilical vein.
2. Umbilical Vein: The oxygenated blood from the placenta enters the fetus through the umbilical vein. This blood is rich in oxygen and nutrients.
3. Ductus Venosus: Some of the blood from the umbilical vein bypasses the liver through a vessel called the ductus venosus, ensuring that the liver doesn’t have to process the full amount of blood flow.
4. Inferior Vena Cava: The majority of oxygenated blood from the umbilical vein enters the fetal inferior vena cava, mixing with deoxygenated blood returning from the lower part of the fetus’s body.
5. Foramen Ovale: In the fetal heart, there is a small hole called the foramen ovale in the septum (wall) between the two atria (upper chambers). This allows some of the oxygenated blood in the right atrium to pass directly into the left atrium, bypassing the fetal lungs.
6. Ductus Arteriosus: Blood leaving the right ventricle is pumped into the pulmonary artery. However, most of it is redirected away from the lungs through a vessel called the ductus arteriosus, which connects the pulmonary artery to the aorta.
7. Aorta: From the aorta, oxygenated blood is distributed to the body, supplying nutrients and oxygen to the fetal tissues.
8. Umbilical Arteries: After circulating through the fetal body, deoxygenated blood returns to the placenta through the umbilical arteries, where it releases waste products and picks up oxygen and nutrients again.

Fetal circulation is designed to provide the developing fetus with oxygen and nutrients while bypassing the non-functional fetal lungs. After birth, several changes occur, including the closure of the foramen ovale and ductus arteriosus, as the baby’s lungs take over oxygen exchange, and the circulatory system adapts to the outside world.