Which fetal structure becomes the ligamentum arteriosum after birth?

• A. Ductus arteriosus
• B. Foramen ovale
• C. Ductus venosus
• D. Umbilical vein

Answer: (A)

The key idea is how fetal circulation remodels after birth. The ductus arteriosus is a vessel that connects the pulmonary artery to the aorta in the fetus, allowing blood to bypass the nonfunctioning lungs. Once born, with the lungs expanding and oxygen levels rising, the ductus arteriosus constricts and eventually fibroses, turning into a fibrous cord known as the ligamentum arteriosum. This remnant stays between the aorta and the pulmonary artery.

Other fetal structures have different fates: the foramen ovale compresses and becomes the fossa ovalis in the interatrial septum; the ductus venosus closes and becomes the ligamentum venosum in the liver; the umbilical vein closes and becomes the ligamentum teres hepatis (round ligament) of the liver.