Increased basal insulin sensitivity in late pregnancy in women carrying a male fetus: a cohort study

BACKGROUND: It has been suggested that fetal sex may be able to modify maternal metabolism and physiology during pregnancy. Recently pregnant women carrying a male fetus were reported to be more insulin sensitive than those carrying females, although related evidence is inconsistent. METHODS: In this study we administered a 75 g oral glucose tolerance test at around week 28 of pregnancy in 813 pregnant women from a contemporary birth cohort (the Cambridge Baby Growth Study), derived surrogate indices of insulin secretion and sensitivity, and related them to the fetal sex. RESULTS: Carrying a male fetus was associated with lower fasting glucose (difference in mean concentrations ≈ 0.1 mmol/L; β′ = 0.063; p = 0.02) and insulin (≈ 1.1 pmol/L; β′ = 0.075; p = 0.01) concentrations but not with post-load glucose or insulin concentrations. Male fetal sex was also associated with lower HOMA IR (≈ 1.08 units; β′ = 0.071; p = 0.02) and higher QUICKI (≈ 1.06 units; β′ = 0.080; p = 0.007) values suggesting increased basal insulin sensitivity. There were no differences in indices of insulin secretion, except for the insulin disposition index which was higher in women carrying a male fetus (≈ 1.15 units; β′ = 0.090; p = 0.007). Birth weights were higher in male offspring. CONCLUSIONS: Women carrying a male fetus were relatively more insulin sensitive in the fasting state and secreted more insulin relative to this degree of insulin sensitivity. These results are consistent with the idea that the fetal sex may be able to modify the maternal glucose-insulin axis.