Associations between the maternal urinary biomarker mixture and boy’s MDI scores assessed with repeated holdout random subset WQSR in the negative direction, based on the concentrations (ng/mL) in the first trimester ( participants, samples) and the averaged concentrations (ng/mL) over the three trimesters ( participants, samples) for participants from a birth cohort study in Wuhan, China, 2014–2017. The models were adjusted for maternal age (categorical), PBMI (categorical), maternal education (categorical), passive smoking (categorical), folic acid supplementation during pregnancy (categorical), parity (categorical), breastfeeding duration (categorical), delivery mode (categorical), and sampling seasons (except for average concentrations). * were considered statistically significant. Details of chemical abbreviations are provided in Figure 1, and the numerical values are listed in Table S9. Note: CI, confidence interval; MDI, mental development index; PBMI, prepregnancy body mass index; WQSR, weighted quantile sum regression.