Toxicological evidence suggests that organophosphate esters (OPEs) may disrupt metabolic processes involved in energy balance and adiposity, yet epidemiological findings remain inconsistent. Among 283 mother-child dyads in the Maternal-Infant Research on Environmental Chemicals (MIREC) cohort, we examined associations between gestational urinary OPE metabolites, including bis(2-chloroethyl) phosphate (BCEP), bis(1-chloro-2-propyl) phosphate (BCIPP), bis(1,3-dichloro-2-propyl) phosphate (BDCIPP), di-n-butyl phosphate (DNBP), and diphenyl phosphate (DPHP), measured at 6-13 and 16-21 weeks of gestation, and seven indicators of adiposity in children aged 7-11 years. We employed adjusted linear and modified Poisson regressions for metabolite-specific estimates and quantile g-computation for joint mixture effects. Associations varied by gestational window. At 6-13 weeks gestation, each doubling in BCIPP concentration was associated with an increased risk of overweight/obesity (aRR = 1.05; 95% CI: 1.02, 1.08) and higher body fat percentage (β = 0.41; 95% CI: 0.35, 0.47). Similarly, each doubling in DNBP was positively associated with waist-to-height (WHtR) Z-scores (β = 0.07; 95% CI: 0.05, 0.09) and body fat percentage (β = 0.39; 95% CI: 0.34, 0.44), whereas doubling of DPHP was associated with higher fat mass index (FMI) Z-scores (β = 0.04; 95% CI: 0.01, 0.07). At 16-21 weeks, BCIPP doubling remained associated with increased risk of overweight/obesity (aRR = 1.03; 1.01, 1.05). Additionally, BDCIPP (β = 0.03; 0.01, 0.05) and DNBP (β = 0.03; 0.01, 0.05) doubling were associated with higher FMI Z-scores, and DNBP was associated with increased waist circumference (WC) Z-scores (β = 0.04; 0.01, 0.06). While the overall mixture effect was null, BCIPP and DNBP were identified as the primary positive contributors to the joint effects. Findings support gestational OPEs as potential obesogens.
