Testing the fuel-mediated hypothesis: maternal insulin resistance and glucose mediate the association between maternal and neonatal adiposity, the Healthy Start study.

Aims/hypothesis: In women who are overweight or obese before or during pregnancy there is an associated risk of increased fetal growth and higher birthweight. The metabolic phenotype of the overweight/obese pregnant woman, characterised by higher than normal insulin resistance (IR) and increased circulating fuels, suggests a mechanism resulting in fetal overnutrition and subsequent increased adiposity. We tested the fuel-mediated hypothesis in an observational pre-birth cohort of 951 mother-offspring pairs, the Healthy Start study.

Methods: We conducted a path analysis to estimate the simultaneous effects of maternal IR and maternal fuels (fasting glucose, triacylglycerol [TG] and NEFA levels) in late pregnancy in mediating the relationship between maternal pre-pregnancy BMI and neonatal adiposity (per cent fat mass [%FM]).

Results: The total effect of maternal BMI on neonatal %FM was significant (total effect 0.16, 95% CI 0.08, 0.22, p < 0.001). The mediated path including maternal IR and glucose levels together accounted for 21% (p < 0.01) of the total effect of maternal BMI on neonatal %FM while the mediating effects of all other fuels were non-significant.

Conclusions/interpretation: Using a novel application of path analysis our data implicate maternal IR and glucose levels as important mediators of the association between maternal and infant adiposity.