Why does the foramen ovale close after birth?

The closure of the foramen ovale after birth is primarily due to the increased left atrial pressure. Before birth, the fetus relies on the foramen ovale to allow blood to bypass the non-functioning lungs, as oxygen is provided through the placenta. During this time, the right atrial pressure is usually higher than that of the left due to the flow of blood coming from the inferior vena cava.

At the moment of birth, several changes occur: the newborn takes its first breaths, leading to the expansion of the lungs and a subsequent decrease in pulmonary vascular resistance. Consequently, this allows increased blood flow to the lungs, resulting in oxygenation of blood and a shift in pressures within the heart. The pressure in the left atrium rises as the lungs become functional and blood returns from the pulmonary veins, surpassing the pressure in the right atrium. This pressure differential pushes the septum primum against the septum secundum, effectively closing the foramen ovale.

While decreased right atrial pressure and increased blood flow to the lungs play pivotal roles in this transition, it is the increased left atrial pressure that directly facilitates the anatomical closure of the foramen ovale, leading to its eventual permanent closure over time. The closure of