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 approximate to 0.1 mmol/L; beta ' = 0.063; p = 0.02) and insulin (approximate to 1.1 pmol/L; beta ' = 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 (approximate to 1.08 units; beta ' = 0.071; p = 0.02) and higher QUICKI (approximate to 1.06 units; beta ' = 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 (approximate to 1.15 units; beta ' = 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.