Which structure connects the ascending aorta and the pulmonary artery during fetal circulation?

During fetal circulation, the ductus arteriosus is the structure that connects the ascending aorta and the pulmonary artery. This vessel plays a critical role in diverting blood away from the non-functioning fetal lungs, allowing it to bypass pulmonary circulation.

In the fetus, the lungs are not yet used for gas exchange, as oxygen is provided by the placenta. The ductus arteriosus acts as a shunt, enabling oxygen-rich blood from the aorta to flow directly into the pulmonary artery and subsequently into the descending aorta, thus supplying the rest of the body without having to travel to the lungs. After birth, the ductus arteriosus normally closes and becomes the ligamentum arteriosum, permanently separating the aorta from the pulmonary artery and establishing normal postnatal circulation.

The other structures mentioned have different roles in fetal circulation. The foramen ovale is responsible for allowing blood to flow from the right atrium to the left atrium, bypassing the lungs. The ductus venosus channels blood from the umbilical vein directly to the inferior vena cava, also bypassing the liver. The umbilical artery carries deoxygenated blood from the fetus back to the placenta. Therefore, the ductus arter