Background The fetuses of women with gestational diabetes mellitus are at risk for macrosomia and its attendant complications. The best method of achieving euglycemia in these women and reducing morbidity in their infants is not known. We compared the efficacy of postprandial and preprandial monitoring in achieving glycemic control in women with gestational diabetes. Methods We studied 66 women with gestational diabetes mellitus who required insulin therapy at 30 weeks of gestation or earlier. The women were randomly assigned to have their diabetes managed according to the results of preprandial monitoring or postprandial monitoring (one hour after meals) of blood glucose concentrations. Both groups were also monitored with fasting blood glucose measurements. The goal of insulin therapy was a preprandial value of 60 to 105 mg per deciliter (3.3 to 5.9 mmol per liter) or a postprandial value of less than 140 mg per deciliter (7.8 mmol per liter). Obstetrical data and information on neonatal outcomes were c...