During the transition at birth when the newborn begins breathing, what causes the foramen ovale to close?

During the transition at birth when the newborn begins breathing, what causes the foramen ovale to close?

• A. Oxygen levels increase
• B. The umbilical cord is clamped
• C. Pressure in the left atria of the heart becomes greater than that in the right atria of the heart
• D. Pulmonary blood vessels constrict, and pulmonary blood pressure increases

Answer: (C)

When the newborn starts breathing, the lungs fill with air and the pulmonary circulation becomes established. Blood returns from the lungs to the left atrium through the pulmonary veins, raising left atrial pressure. At the same time, clamping the umbilical cord stops placental blood flow, reducing venous return to the right atrium and lowering its pressure. This shift makes the left atrial pressure exceed the right atrial pressure, pushing the flap of tissue that forms the foramen ovale against the septum and functionally closing the opening. Over time, this seal becomes permanent as fibrous tissue forms. Oxygenation and cord clamping contribute to the change, but the key trigger is the new left-right atrial pressure gradient caused by lung aeration and loss of placental circulation. Pulmonary pressure actually decreases after birth as the lungs expand, not increases.

When the newborn starts breathing, the lungs fill with air and the pulmonary circulation becomes established. Blood returns from the lungs to the left atrium through the pulmonary veins, raising left atrial pressure. At the same time, clamping the umbilical cord stops placental blood flow, reducing venous return to the right atrium and lowering its pressure. This shift makes the left atrial pressure exceed the right atrial pressure, pushing the flap of tissue that forms the foramen ovale against the septum and functionally closing the opening. Over time, this seal becomes permanent as fibrous tissue forms. Oxygenation and cord clamping contribute to the change, but the key trigger is the new left-right atrial pressure gradient caused by lung aeration and loss of placental circulation. Pulmonary pressure actually decreases after birth as the lungs expand, not increases.