What major change occurs in the circulatory system at birth?

At birth, a significant transformation occurs in the circulatory system as the fetus transitions to an independent life outside the womb. One of the most critical events in this change is the closure of the ductus arteriosus. Prior to birth, the ductus arteriosus connects the pulmonary artery to the aorta, allowing blood to bypass the non-functioning fetal lungs, which are filled with fluid and not yet supplying oxygen.

When the baby takes its first breaths, the lungs inflate, leading to a decrease in pressure within the pulmonary arteries. This change in pressure, along with increased oxygen levels in the blood, prompts the ductus arteriosus to constrict and eventually close within the first few days of life. This closure is essential for proper circulation, redirecting blood flow to the lungs for oxygenation, and establishing the normal postnatal circulatory pathways.

The other options refer to related changes but do not capture the primary event that defines this crucial transition. For instance, while there is a decrease in placental blood supply as the umbilical cord is clamped, leading to more blood returning to the heart, it doesn’t encapsulate the pivotal alteration in vascular structure. Similarly, while the foramen ovale does open in u