What triggers the closure of the ductus arteriosus immediately after birth?

• A. Increase in CO2 and decrease in prostaglandins
• B. Decrease in oxygen and decrease in prostaglandins
• C. Increase in oxygen and decrease in prostaglandins
• D. Decrease in CO2 and increase in oxygen

Answer: (C)

The closure of the ductus arteriosus immediately after birth is primarily triggered by an increase in oxygen levels and a decrease in prostaglandins. During fetal life, the ductus arteriosus serves as a shunt, allowing blood to bypass the non-functioning lungs by connecting the pulmonary artery to the aorta.

After birth, the baby takes its first breaths, leading to an increase in systemic oxygen levels. This increase in oxygen concentration is critical as it promotes vasoconstriction of the ductus arteriosus, facilitating its closure. Additionally, the decrease in prostaglandins, which are vasodilators that keep the ductus arteriosus patent during fetal life, further aids in the closure process.

Together, these changes help to re-establish normal pulmonary circulation and direct blood flow to the lungs for oxygenation, marking a significant transition in the newborn's circulatory system. Understanding this physiological change is crucial in neonatal care, as the persistence of a patent ductus arteriosus can lead to complications.