What happens to the fetal blood flow after the umbilical cord is clamped at birth?

• A. Blood pressure rises and systemic vascular resistance decreases
• B. Blood pressure falls and the placenta is re-engaged
• C. Rises in blood pressure and increased resistance occur
• D. The ductus arteriosus closes immediately

Answer: (C)

After the umbilical cord is clamped at birth, the physiological changes that occur are significant. The clamping of the cord interrupts the placental circulation, leading to an increase in systemic vascular resistance due to the cessation of low-resistance placental blood flow. When the blood flow through the umbilical vessels is stopped, two important factors come into play: the baby's lungs begin to expand with air, and with that expansion, pulmonary vascular resistance decreases. This transition causes blood flow to shift from the placental circuit to the systemic circuit.

As a result of these changes, systemic blood pressure tends to rise. The increase in blood pressure is a direct response to the increased systemic vascular resistance, which is critical for ensuring adequate perfusion to the vital organs of the newborn. Immediately after the birth and obtaining the increased systemic resistance, the blood pressure does not just stabilize; it also often rises in the immediate postnatal period due to these adaptations.

The response of the ductus arteriosus is also a part of this transition, as it usually closes in the days following birth, but the immediate hemodynamic effects after clamping the cord are characterized by increased blood pressure and increased systemic vascular resistance. Understanding this transition is fundamental in perin