Maternal body mass index, offspring body mass index, and blood pressure at 18 years: a causal mediation analysis.

OBJECTIVE Understanding the natural history of hypertension is key to identifying prevention strategies. Previous work suggests that in utero exposures and offspring anthropometrics may play a role. This study examined the relationship between maternal pre-pregnancy body mass index (BMI) and the mediating role of childhood and adolescent BMI on offspring blood pressure at 18 years. METHODS We performed multivariable regression and causal mediation analyses within 3217 mother - offspring pairs from the Avon Longitudinal Study of Parents and Children prospective birth cohort. The main exposure was maternal pre-pregnancy BMI, and the outcome was offspring blood pressure at 18 years of age categorized as normal or elevated. Latent trajectory analysis was used to quantify the mediator, offspring BMI trajectories, derived from multiple measurements throughout childhood and adolescence. Mediation analyses were repeated using current offspring BMI at 18 years as a continuous variable. RESULTS Multivariable logistic regression revealed that for every 1 unit increase in maternal BMI, the risk of elevated blood pressure at 18 years of age increased by 5% (aOR: 1.05, 95% CI: 1.03-1.07; p < 0.001). The strength of this association was reduced after adjusting for offspring BMI trajectory (aOR: 1.03, 95% CI: 1.00-1.05; p = 0.017) and eliminated after adjusting for offspring BMI at 18 years (aOR: 1.00; 95% CI: 0.98-1.03; p = 0.70). Causal mediation analysis confirmed offspring BMI at 18 years as a mediator, where BMI trajectory accounted for 46% of the total effect of maternal BMI on elevated offspring blood pressure and current BMI account for nearly the entire effect. CONCLUSIONS Maternal pre-pregnancy BMI is associated with an increased risk of elevated blood pressure in offspring at 18 years of age although it appears to be entirely mediated by offspring BMI.