Limited Impact of Fetal Sex and Maternal Body Mass Index on Fetal and Maternal Insulin Resistance and Lipid Metabolism: Findings from the PEARs Study

Anthony R. Rafferty, Aisling A. Geraghty, Maria A. Kennelly, Eileen C. O’Brien, Reshma Merin Reji, John Mehegan, Ricardo Segurado, Thomas Smith, Orla Maguire, Martina Cronin, Fionnuala M. McAuliffe

The intrauterine environment can have a significant impact on fetal and maternal well-being, both during pregnancy and in later life. We aimed to identify how fetal sex and maternal body mass index (BMI) influence insulin resistance and metabolic function during pregnancy with maternal BMI > 25 kg/m2. This secondary analysis assessed data from the PEARS-randomized controlled trial that recruited pregnant women with body mass indexes 25-39.9 kg/m2. Longitudinal measurements of maternal and fetal insulin resistance and metabolic function were recorded throughout pregnancy. Regression models tested the effects of fetal sex and maternal BMI on markers of metabolic function and insulin regulation. A total of 484 women and their newborns (252 (52%) males vs. 232 (48%) females) were included in the analysis. A total of 333 (69%) women were overweight and 151 (31%) were obese. Male newborns were heavier and larger than females, and had a higher rate of instrumental delivery. Males had a lower LDL, but no other markers of insulin resistance or metabolic function were affected by fetal sex. Women with obesity had elevated markers of insulin resistance and metabolic dysfunction compared with women that were overweight, but maternal BMI did not impact these variables in the fetus. Fetal sex did not impact maternal and fetal metabolic parameters in women with BMI > 25 kg/m2. However, a higher BMI caused increasingly deranged maternal blood lipid concentrations and markers of insulin resistance as pregnancy progressed. Lipid monitoring and interventions to reduce lipids during pregnancy therefore require further evaluation.