Effect of sustained maternal hyperglycaemia on the fetus in normal and diabetic pregnancies.

The effect of prolonged maternal hyperglycaemia on fetal plasma glucose and insulin concentrations was investigated in eight normal and nine diabetic patients. It was found that under fasting conditions the fetal glucose concentration in gestational diabetic pregnancies tended to be lower than in normal pregnancies. Insulin measurements suggested that this may be due to fetal hyperinsulinism in the diabetic group. During glucose infusion, regardless of the degree of maternal hyperglycaemia, the fetal glucose concentration was limited in 12 out of 13 cases to less than 200 mg/100 ml, with only small differences between normal and diabetic pregnancies. It is proposed that the placenta prevents unlimited transport of glucose to the fetus; yet in diabetic pregnancies a sequence of increased maternal-fetal glucose transport, fetal hyperinsulinism, and fetal hypoglycaemia may contribute to the observed perinatal mortality.