Does Fat Beget Fat? The Relationship between Maternal Pre-Pregnancy BMI and Preschool Obesity

Erin K. Fletcher, Harvard University
Susan L. Averett, Lafayette College

The increasing prevalence of obesity during pregnancy raises concerns over the intergenerational transmission of obesity and its potential to exacerbate the current obesity epidemic. The fetal origins hypothesis posits that the intrauterine environment may have lasting effects on children's outcomes and mother's pre-pregnancy obesity has been associated with pediatric obesity. However, previous research is largely based on comparing individuals across families and hence cannot control for unobservable factors associated with both maternal and child obesity. We use within-family comparisons and instrumental variables to identify the effect of maternal pre-pregnancy obesity on obesity in children. Consistent with extant research, OLS models that rely on across-family comparisons indicate a significant correlation between maternal pre-pregnancy obesity and child obesity. However, maternal fixed effects render those associations insignificant. Instrumenting for mother’s BMI with her sisters’ BMI confirms the null result indicating that the in utero transmission of obesity is likely not driving the increase in childhood obesity.