Perinatal Islet Function in Gestational Diabetes: Assessment by Cord Plasma C-Peptide and Amniotic Fluid Insulin

Abstract

We have attempted to use perinatal islet performance as an index of the impact of maternal fuels during fetal development. Accordingly, we analyzed cord plasma for C-peptide and amniotic fluid (secured several weeks before delivery) for immunoreactive insulin in infants of mothers with normal metabolism (NM), gestational diabetes (GDM), and tightly regulated White Class B or Class C insulin-dependent diabetes mellitus (IDDM). We tried to subdivide mothers with GDM on the basis of severity by distinguishing between those with fasting plasma glucose within the normal range for pregnancy (i.e., less than 105 mg/dl and those with fasting plasma glucose of 105 mg/dl or greater). Most of the latter were treated with insulin whereas the former received diet alone. We found that cord plasma levels of C-peptide in infants of mothers with GDM < 105, GDM ≥ 105, and IDDM did not differ significantly from one another; all were approximately twofold greater than in infants from mothers with NM. Values for insulin and ratios of insulin/glucose in amniotic fluid were also increased and to a similar degree in all three diabetic groups; all exceeded the findings in the NM group. Our results indicate that islet function is enhanced at birth in the offspring of mothers with even the mildest forms of untreated gestational diabetes (i.e., GDM < 105) to a degree that is not appreciably different than in more severe forms of diabetes receiving tightly regulated insulin therapy. The augmented B-cell secretion cannot be ascribed to intrapartum events, since similar changes were also found in amniotic fluid secured several weeks before delivery. We conclude that neonatal insulin secretion may constitute an exquisitely sensitive index of the effects of ambient fuels during intrauterine life. Neonatal B-cell function thereby may provide a useful yardstick for the retrospective evaluation of maternal glucoregulation during late gestation.