Mosby's Canadian Practical Nurse (PN) Practice Test

Closure of the foramen ovale at birth is driven by a shift in atrial pressures when the newborn begins breathing. Once the first breath is taken, the lungs expand and pulmonary vascular resistance falls, allowing more blood to flow to the lungs and return to the left atrium. This increases left atrial pressure relative to right atrial pressure, and the higher pressure on the left side pushes the flap-like opening in the atrial septum shut, producing functional closure. Over time, the septum becomes a permanent barrier as the foramen ovale tissue seals into the fossa ovalis.

The other factors don’t explain the mechanism as directly. While clamping the umbilical cord contributes to the cardiovascular transition, the closure itself is due to the new pressure gradient from the lungs’ increased blood return to the left atrium. Also, pulmonary vascular resistance decreases after birth, not increases, so that change wouldn’t trigger closure.