The foramen ovale closes after birth due to an increase in

Prepare for the Fetal Echocardiography Test. Utilize flashcards and multiple-choice questions that come with hints and explanations. Ace your exam preparation!

The main idea is that birth reverses the atrial pressure gradient. As the newborn begins breathing, the lungs expand and pulmonary vascular resistance falls, increasing blood flow through the lungs and returning more oxygenated blood to the left atrium. This raises left atrial (left heart) pressure relative to right atrial pressure. When the left atrial pressure becomes higher, the flap of the foramen ovale is pressed closed against the opening, functionally sealing it. Over time the closure becomes anatomic as the septum primum and secundum fuse.

Think of it as the pressure shift driving closure: left-sided pressures rise after birth due to increased pulmonary venous return, while the right-sided pressures do not rise enough to keep the opening open. A higher right-sided pressure would oppose closure, and a rise in pulmonary vascular resistance wouldn’t occur after birth (it falls), which also helps the process. Respirations help by expanding the lungs, but the key trigger is the rise in left atrial pressure relative to the right.