What physiological change occurs in the neonate's plasma insulin levels after the umbilical cord has ceased functioning?

After the umbilical cord ceases functioning, the physiological change in a neonate's plasma insulin levels is a decrease. This occurs primarily because the neonate is transitioning from a continuous supply of glucose and insulin from the mother, which was provided via the placenta, to an independent metabolic state.

Once the cord is clamped and the neonatal circulation becomes fully independent, the immediate source of maternal glucose and insulin is eliminated. The neonate's own pancreas must then begin to regulate blood glucose levels and respond to changing conditions, leading to a reduction in circulating insulin levels initially as the body adjusts.

This decrease is a crucial part of the transition to extrauterine life, as the neonate's hepatic function and glucose metabolism start to take over. In the absence of the placental supply, the decrease in insulin is necessary for the proper management of the infant's blood sugar levels as they begin to feed and metabolize nutrients independently.