['Offspring of mothers with impaired glucose tolerance are far more likely to develop type 2 diabetes. We tested the hypothesis that maternal glucose tolerance in pregnancy affects fetal insulin sensitivity or beta-cell function.', 'In a prospective singleton pregnancy cohort study, we analyzed glucose, insulin, and proinsulin concentrations in maternal blood at the 50-g oral glucose tolerance test (OGTT) at 24-28 weeks of gestation and in venous cord blood (n = 248). The cord blood glucose-to-insulin ratio and proinsulin concentration were used as indicators of fetal insulin sensitivity and the proinsulin-to-insulin ratio was used as an indicator of fetal beta-cell function.', 'Higher OGTT blood glucose levels were associated with significantly lower cord plasma glucose-to-insulin ratios (r = -0.31, P < 0.001) and higher proinsulin concentrations (r = 0.31, P < 0.001) but not with proinsulin-to-insulin ratios. In a comparison of gestational diabetic (n = 26) versus euglycemic pregnancy, cord blood glucose-to-insulin ratios were substantially lower (geometric mean 10.1 vs. 20.0 mg/dl/microU/ml; P < 0.001), whereas proinsulin concentrations were much higher (24.4 vs. 13.8 pmol/l; P < 0.001), despite similar cord blood glucose concentrations indicating adequate management of diabetes. The differences remained significant after controlling for prepregnancy and fetal adiposity, family history of diabetes, gestational age, and other potential confounders. Significant changes in the glucose-to-insulin ratio and proinsulin concentration were also observed in obese (n = 31) mothers, but the differences became not statistically significant after adjustment for maternal glucose tolerance and fetal adiposity.'] Does maternal glucose tolerance in pregnancy affect fetal insulin sensitivity?