Individual and Joint Effects of Early-Life Ambient [Formula: see text] Exposure and Maternal Prepregnancy Obesity on Childhood Overweight or Obesity

BACKGROUND: Although previous studies suggest that exposure to traffic-related pollution during childhood increases the risk of childhood overweight or obesity (COWO), the role of early life exposure to fine particulate matter (aerodynamic diameter [Formula: see text]; [Formula: see text]) and its joint effect with the mother's prepregnancy body mass index (MPBMI) on COWO remain unclear. OBJECTIVES: The present study was conducted to examine the individual and joint effects of ambient PM(2.5) exposures and MPBMI on the risk of COWO. METHODS: We estimated exposures to ambient [Formula: see text] in utero and during the first 2 y of life (F2YL), using data from the U.S. Environmental Protection Agency’s (EPA's) Air Quality System matched to residential address, in 1,446 mother–infant pairs who were recruited at birth from 1998 and followed up prospectively through 2012 at the Boston Medical Center in Massachusetts. We quantified the individual and joint effects of [Formula: see text] exposure with MPBMI on COWO, defined as the child's age- and sex-specific BMI [Formula: see text] [Formula: see text] at the last well-child care visit between 2 and 9 y of age. Additivity was assessed by estimating the reduced excess risk due to interaction. RESULTS: Comparing the highest and lowest quartiles of [Formula: see text] , the adjusted relative risks (RRs) [95% confidence intervals (CIs)] of COWO were 1.3 (95% CI: 1.1, 1.5), 1.2 (95% CI: 1.0, 1.4), 1.2 (95% CI: 1.0, 1.4), 1.3 (95% CI: 1.1, 1.6), 1.3 (95% CI: 1.1, 1.5) and 1.3 (1.1, 1.5) during preconception; the first, second, and third trimesters; the entire period of pregnancy; and F2YL, respectively. Spline regression showed a dose–response relationship between [Formula: see text] levels and COWO after a threshold near the median exposure ([Formula: see text]). Compared with their counterparts, children of obese mothers exposed to high levels of [Formula: see text] had the highest risk of COWO [[Formula: see text] , relative excess risk due to interaction (RERI) not significant]. CONCLUSIONS: In the present study, we observed that early life exposure to [Formula: see text] may play an important role in the early life origins of COWO and may increase the risk of COWO in children of mothers who were overweight or obese before pregnancy beyond the risk that can be attributed to MPBMI alone. Our findings emphasize the clinical and public health policy relevance of early life [Formula: see text] exposure. https://doi.org/10.1289/EHP261