pediatrics
Perinatal Physiology
Neonatal Endocrine Function
(See also Overview of the Endocrine System .) The fetus depends completely on the maternal supply of glucose via the placenta and does not contribute to glucose production. The fetus begins to build a hepatic glycogen supply early in gestation, accumulating most glycogen stores during the second half of the third trimester. The neonate’s glucose supply terminates when the umbilical cord is cut; concurrently, levels of circulatingepinephrine,norepinephrine, andglucagonsurge, whileinsulinlevels decline. These changes stimulate gluconeogenesis and mobilization of hepatic glycogen stores. In healthy, term neonates, glucose levels reach a nadir 30 to 90 minutes after birth, after which neonates are typically able to maintain normal glucose homeostasis. Infants at highest risk of Neonatal Hypoglycemia include those with reduced glycogen stores ( In the fetus, the placenta is the main source of minerals necessary for bone mineralization by active transport of calcium, magnesium, and phosphorous that is stimulated by maternal and placentalparathyroid hormone(PTH) and PTH-related protein (PTHrP). In the neonate, the kidneys and intestines control the delivery and excretion of these minerals. Fetal PTH production is suppressed by high circulating calcium levels supplied by the placenta. When the umbilical cord is cut at birth, the placental infusion of calcium ceases, causing a 20 to 30% fall in serum calcium levels, reaching a trough level at 24 to 48 hours. Simultaneously, serum phosphorous rises. There is a lag before the neonatal parathyroid glands become fully responsive (physiologic hypoparathyroidism) and serum PTH surges in response to the decline in serum calcium. Calcium and phosphorous levels then stabilize at neonatal levels and skeletal mineral homeostasis becomes controlled by the intestines and kidneys. 1.Kovacs CS: Calcium, phosphorus, and bone metabolism in the fetus and newborn.Early Hum Dev91(11):623–628, 2015. doi: 10.1016/j.earlhumdev.2015.08.007 