Fetal hyperinsulinism at 14-20 weeks and subsequent gestational diabetes.

OBJECTIVE: To examine the predictive value of amniotic fluid (AF) insulin at 14-20 weeks' gestation for subsequent gestational diabetes and macrosomia in unselected gravidas 35 years or older at time of genetic amniocentesis.
METHODS: We identified 296 pregnancies through stored AF samples from genetic amniocenteses (collected March 1987 through August 1992) in women meeting the following criteria: age 35 years or older, amniocentesis at 14-20 weeks, performance of a 50-g glucose challenge test, and adequate delivery data.
RESULTS: A modified double-antibody radioimmunoassay reliably measured AF insulin with a detection limit of 0.35 microU/mL. Pregnant women in whom gestational diabetes was later diagnosed had higher median AF insulin levels than women who did not (0.60 versus 0.42 microU/mL, respectively; P = .026). A stepwise logistic regression analysis of gestational age at amniocentesis, maternal second-trimester weight, maternal age, and log AF insulin value on gestational diabetes showed only AF insulin to have a significant association with gestational diabetes (P = .004). Seven of 21 cases of gestational diabetes had AF insulin values exceeding the 95th percentile (1.33 microU/mL) compared with only 14 of 275 women with normal glucose tolerance (P < .001). Amniotic fluid insulin did not predict macrosomia in either nondiabetic or gestational diabetic pregnancies.
CONCLUSION: Gestational diabetes is associated with increased AF insulin at 14-20 weeks, suggesting augmentation of fetal insulin production in the early fetal period in at least some cases of gestational diabetes.