FETAL PROINSULIN AND BIRTH-WEIGHT

In both diabetic and non-diabetic pregnancies fetal insulin is an impo rtant anabolic hormone. Fetal hyperinsulinaemia is associated with acc elerated fetal growth and increased birth weight. Insulin and C-peptid e concentrations in both umbilical cord and amniotic fluid reflect fet al beta-cell secretion and are correlated with birth weight. In the pr esent study umbilical venous proinsulin and insulin concentrations wer e measured in 54 term infants born to women with and without mild dist urbances of glucose tolerance. Umbilical venous cord proinsulin, assay ed using a highly specific immunoradiometric assay, was independently correlated with infant birth weight (Rho = 0.53, p < 0.0001) and birth percentile (Rho = 0.65, p < 0.0001). The correlation between birth we ight and birth percentile weight with umbilical venous insulin, measur ed using a non-specific insulin assay, was lost following correction f or the influence of proinsulin. Umbilical venous cord proinsulin appea rs to be a good indicator of fetal beta-cell activity, and in this stu dy, a superior marker to insulin assayed using a non-specific insulin radioimmunoassay. The longer half-life of proinsulin compared with ins ulin may contribute to proinsulin being a more robust marker of overal l fetal beta-cell activity than insulin.