Metabolism of glucose in the fetus

Glucose is a vital substrate for the growing and developing fetus. It is required by most cells for oxidative and nonoxidative ATP production and serves as a precursor for other carbon-containing compounds. It is the primary fuel used for several specialized cells and is the major fuel used by the brain. Its storage in the liver as glycogen provides a means by which glucose homeostasis can be maintained, particularly during the neonatal period. The fetal requirement for glucose is met almost, if not entirely, by transplacental transport from the mother to the fetus. At birth, there is an abrupt loss of the maternal supply of substrates and nutrients and the newborn has to mobilize glucose and other substrates to meet its energy needs.

A number of studies in a variety of species, including humans, have shown that fetal plasma glucose concentrations are significantly lower than that of the mother. Furthermore, there is a direct relationship between maternal and fetal plasma glucose concentrations and the supply of glucose to the fetus is highly dependent upon maternal glycemia. Thus, the supply of glucose to the fetus is likely to be diminished in the case of maternal hypoglycemia and to be increased in the case of maternal hyperglycemia. However, the placenta has a large capacity for glucose storage in the form of glycogen which blunts glucose transfer to the fetus when significant maternal hyperglycemia occurs.