What physiological change occurs when the umbilical cord is clamped?

When the umbilical cord is clamped, the physiological transition that occurs is an increase in systemic vascular resistance. Prior to clamping, the fetus is dependent on placental circulation, which allows for low resistance in the systemic circulation due to the presence of the placenta providing oxygen and nutrients. Once the umbilical cord is clamped, this external vascular connection is severed, leading to a significant increase in systemic vascular resistance as the neonate’s own circulatory system must now accommodate the demands of the body without the low-pressure placental circuit.

This change occurs alongside an increase in blood volume returning to the heart from systemic circulation, which helps to establish effective heart function and normal blood pressure in the neonate. The combined effect of the clamping of the umbilical cord and the newborn's breathing efforts contributes to expanded lung volume, which subsequently reduces pulmonary resistance and enhances oxygenation. Thus, the increase in systemic vascular resistance is a critical change that supports the transition to extrauterine life.