BackgroundAlthough experiments in animals suggest that phthalates may have obesogenic effects, studies on prenatal exposure in children show inconsistent results.MethodsWe measured urinary concentrations of 11 phthalate metabolites collected twice during pregnancy from mothers participating in the Center for the Health Assessment of Mothers and Children of Salinas (CHAMACOS) cohort study (N=345). Height, weight, waist circumference, and percent body fat were assessed in their children between 5 and 12 years of age. We used generalized estimating equations to examine associations at each age and tested for interaction by sex.ResultsMetabolites of diethyl phthalate (DEP), di-n-butyl phthalate (DBP), butyl benzyl phthalate, and di(2-ethylhexyl) phthalate (DEHP) were positively associated with BMI z-score, waist circumference z-score, and percent body fat at multiple ages. At age 12, we observed increased odds of being overweight/obese with each doubling of prenatal concentrations of DEP (odds ratio=1.3; 95% confidence intervals: 1.1, 1.4), DBP (1.2; 1.0, 1.4), and DEHP (1.3; 1.0, 1.6) metabolites. Results were similar in boys and girls except for DBP metabolites and the non-specific metabolite mono-(3-carboxypropyl) phthalate, which showed positive associations only in boys.ConclusionIn utero exposure to certain phthalates is associated with increased BMI and risk for overweight/obesity in childhood.Pediatric Research advance online publication, 31 May 2017; doi:10.1038/pr.2017.112.