What happens to the ductus arteriosus after birth?

After birth, the ductus arteriosus undergoes a closure process, ultimately becoming the ligamentum arteriosum. In fetal life, the ductus arteriosus is a vital structure that connects the pulmonary artery to the descending aorta, allowing blood to bypass the non-functioning fetal lungs. Once the baby is born and takes its first breaths, the lungs expand and begin to function, which alters blood flow dynamics in the circulatory system.

The increase in oxygen levels and the drop in circulating prostaglandins contribute to the constriction of the ductus arteriosus. Over several days to weeks after birth, this constriction leads to the permanent closure of the ductus arteriosus, resulting in the formation of the ligamentum arteriosum. This transformation is a normal part of postnatal circulatory adaptation as the body shifts from fetal to neonatal circulation.

The other scenarios presented do not accurately describe the physiological changes that occur: the ductus does not enlarge after birth, nor does it remain open for several months or become part of the aortic arch. Instead, its primary role transitions to a remnant structure, the ligamentum arteriosum, which has no significant function in the adult circulatory system.