Metabolic adaptations of the fetus and newborn.

During the perinatal period metabolic adaptations take place which insure that substrates for energy production and growth are available in the immediate postnatal period. The fetus receives a constant infusion of glucose, fatty acids and protein by the placenta. Late in gestation the accumulation of storage fuels such as glycogen and adipose tissue anticipate the abrupt cessation of substrate supply from the placenta at the time of birth. Postnatally an increase in endogenous production of glucose in the form of glycogenolysis and gluconeogenesis become important for maintenance of glucose homeostasis. Increase utilization of fatty acids in ketone bodies as energy substrates also become important in the postnatal period. These metabolic adaptations are mediated by the development of new enzyme activities as well as by changes in hormonal millieu and substrate availability.