During transition from fetal to neonatal circulation, what happens when the umbilical cord is clamped, and which structures normally close?

• A. Umbilical cord clamping decreases systemic vascular resistance; patent foramen ovale and ductus arteriosus close; ductus venosus closes.
• B. Clamping the umbilical cord increases systemic vascular resistance; patent foramen ovale and ductus arteriosus close; ductus venosus closes.
• C. Clamping has no effect on SVR; PFO stays open.
• D. Clamping increases venous return; ductus venosus reopened.

Answer: (B)

When the umbilical cord is clamped, the placenta, a low-resistance vascular bed, is removed from the circulation. This abrupt removal raises systemic vascular resistance as the baby’s circulation becomes independent from the placental circuit. At the same time, the lungs begin to take over oxygenation, so pulmonary vascular resistance falls and pulmonary blood flow increases. This shift in pressure and flow causes the heart to change the pressures in the heart chambers: left atrial pressure rises relative to right atrial pressure, promoting the closure of the foramen ovale. The ductus arteriosus also constricts and closes as oxygen tension rises and prostaglandin levels fall, stopping the connection between the pulmonary artery and the aorta. The ductus venosus closes because the placental circulation is gone; blood that previously bypassed the liver via the ductus venosus now circulates through the liver.

So the key sequence is: cord clamping increases systemic vascular resistance, the foramen ovale and ductus arteriosus close, and the ductus venosus closes.