Joint effects of maternal smoking and ambient air pollution on neonatal adiposity and BMI trajectories in the Healthy Start study

Abstract

Background: Exposure to environmental toxicants during pregnancy, including maternal smoking and ambient air pollution, may influence early-life growth. These exposures may work synergistically, but few studies have explored this potential interaction. We sought to explore the potential interaction between fetal exposure to tobacco and O3 and PM2.5 with birth weight and neonatal adiposity, as well as BMI growth trajectories through age 3 years.Methods: We followed 526 mother-child pairs enrolled in the Healthy Start cohort, who were born full-term (≥37 weeks gestation). Maternal urinary cotinine was measured at ~27 weeks gestation. Maternal residential address at study enrollment was used to estimate average concentrations of fine particulate matter (PM2.5) and ozone (O3) by trimester and throughout pregnancy. Neonatal adiposity (fat mass percentage) was measured using air displacement plethysmography. Child weight and length/height were abstracted from medical records. Interaction was assessed by including cotinine categories (<31.5 versus ≥31.5 ng/mL [indicating active smoking]), PM2.5 or O3 categories (first and second tertiles versus third tertile), and their product term in linear regression models, with birth weight and infant adiposity as separate outcomes. Mixed-effects regression models estimated the association between cotinine categories, PM2.5/O3 categories, and their product with childhood BMI.Results: Our interaction results suggest that the rate of BMI growth among offspring exposed to both maternal smoking and higher PM2.5 exposure in the third trimester (PM2.5≥8.1 μg/m3) was higher than would be expected due to the individual exposures alone (0.6 kg/m2 per year; 95% CI: 0.1, 2.3; p for interaction=0.03). We did not detect interactions between maternal smoking and O3 or PM2.5 at any other time point on birth weight, neonatal adiposity, or BMI growth trajectories.Conclusions: Although PM2.5 was well below EPA standards, exposure during the third trimester may influence early-life growth when combined with maternal smoking.