Fetal circulation refers to the unique system of blood flow in a developing fetus. Unlike adults, fetuses do not use their lungs for oxygen; instead, they receive oxygen-rich blood from the placenta through the umbilical cord. This blood bypasses the lungs via two key structures: the foramen ovale, which allows blood to flow between the right and left atria, and the ductus arteriosus, which connects the pulmonary artery to the aorta. As the fetus grows, its circulatory system prepares for birth. After delivery, the foramen ovale and ductus arteriosus close, redirecting blood flow to the lungs for oxygenation. This transition is crucial for the newborn's adaptation to breathing air and marks the shift from fetal to postnatal circulation.