What is the function of the foramen ovale in fetal circulation?

The foramen ovale serves a critical role in fetal circulation by allowing oxygenated blood, which comes from the placenta, to bypass the non-functioning lungs of the fetus. In utero, the fetus does not use its lungs for oxygen exchange as it relies on the mother’s placenta to provide oxygen-rich blood.

The foramen ovale is an opening between the right and left atria of the heart. When blood returns to the fetus from the placenta through the umbilical vein, it enters the right atrium. Instead of being pumped into the right ventricle and sent to the lungs, a significant portion of this blood flows through the foramen ovale into the left atrium, then to the left ventricle, and out to the rest of the body, effectively allowing most of the oxygenated blood to bypass the pulmonary circulation where the lungs would be if they were functioning.

This bypass is crucial, as the lungs are filled with fluid at this stage and are not yet performing their respiratory function. After birth, the foramen ovale typically closes as the newborn begins to breathe air and the circulation pattern changes, thereby directing blood flow through the lungs for oxygenation.

In contrast, the other answers do not accurately describe