Fetal insulin balance: gestational diabetes and postpartal screening.

It must be determined whether high neonatal birth weight (greater than or equal to 4000 g) is due to genetic factors or to a disorder of maternal carbohydrate metabolism. Oral glucose tolerance tests are known to be unreliable during the puerperium. If the mother's carbohydrate metabolism was disturbed during pregnancy, neonatal overweight may result from fetal hyperinsulinism. This can be diagnosed by determining the insulin in the umbilical cord blood. Mature neonates of metabolically healthy women show an insulin level of 9.2 +/- 4.4 microU/ml (N = 180) in the umbilical cord blood. The third, tenth, 50th, 90th, and 97th percentiles were calculated as 1.4, 4.3, 8.8, 15.4, and 17.7 microU/ml, respectively. With insulin values over 20 microU/ml in the umbilical cord blood, a disturbance of maternal carbohydrate metabolism during pregnancy is likely. Among 4560 births in one year, 335 neonates weighed 4000 g and more, corresponding to a proportion of 7.35%. In one quarter of the infants over 4000 g, high birth weight was associated with fetal hyperinsulinism. This corresponds to a frequency of 1.8% of all births.