CARBOHDRATE METABOLISM IN THE FETUS AND THE NEWBORN

Fetal carbohydrate metabolism: its clinical importance

A basic understanding of fetal nutrition and metabolism is essential in the clinical management of the obstetric patient. The fetus depends upon a constant infusion of glucose for energy production and growth. Maternal glucose is the prime source of this nutrient. Alterations in maternal carbohydrate homeostasis will lead to changes in fetal metabolism. In diabetes mellitus, hyperglycemia may produce hyperinsulinemia and macrosomia. The growth-retarded fetus may have a decreased supply of maternal glucose and reduced amounts of hepatic glycogen and adipose tissue. The fetus must depend upon these stores for survival during periods of intrauterine hypoxia. In the newborn period, hypothermia and hypoxia may rapidly deplete energy reserves. With this information, the clinician may more knowledgeably manage dietary demands in the antepartum patient, fetal distress during labor, and the immediate newborn period.

Glucose metabolism by human placental villi

1. Glucose phosphorylation rates of about 1 mumole/g./min. have been measured at room temperature in homogenates of human placental chorionic villi, and these rates are relatively constant throughout gestation. 2. This reaction has an apparent K(m) for glucose of 3x10(-5)m both in early and term placenta. 3. Human foetal membranes, the amnion and chorion, also phosphorylate glucose at a rate about equal to that of the placenta. 4. On incubation of intact bits of villus tissue from 8-12-week or full-term placenta with labelled pyruvate, followed by paper chromatography of the tissue extract, the following distribution of label was observed: residual pyruvate, 40-60%; lactate, 30-50%; glucose, 6%; fructose, 7%; sorbitol, 0.6%. 5. The concept of the placenta acting as a foetal liver during early pregnancy is inconsistent with the observation that glucose production by this organ persists up to term.