Prenatal assessment of fetal outcome by amniotic fluid C-peptide levels in pregnant diabetic women.

Amniotic fluid C-peptide (AFCP), insulin, and glucose levels were measured in 33 diabetic and 126 nondiabetic pregnant women at greater than or equal to 36 weeks' gestation. Levels of AFCP distinguished diabetic from nondiabetic patients more reliably than amniotic fluid (AF) insulin or glucose. Levels of AFCP in diabetic patients correlated well with infant birth weight adjusted for gestational age (large for gestational age greater than adequate for gestational age), degree of diabetic control (fair to poor control greater than good control), or diabetogenic infant morbidity, but did not correlate with classes of diabetes within the limits of the population studied. We conclude that AFCP is a useful prognostic index for predicting fetal outcome in diabetic pregnancies. A level of AFCP of greater than or equal to 1.0 pmoles/ml is associated with an increased risk of macrosomia in infants of diabetic mothers.