Background: Polybrominated diphenyl ethers (PBDEs) are lipophilic flame retardants that bioaccumulate in humans. Child serum PBDE concentrations in California are among the highest worldwide. PBDEs may be associated with obesity by disrupting endocrine systems.

Objective: In this study, we examined whether pre- and postnatal exposure to the components of pentaBDE mixture was associated with childhood obesity in a population of Latino children participating in a longitudinal birth cohort study in the Salinas Valley, California.

Methods: We measured PBDEs in serum collected from 224 mothers during pregnancy and their children at 7 years of age, and examined associations with body mass index (BMI) at age 7 years.

Results: Maternal PBDE serum levels during pregnancy were associated with higher BMI z -scores in boys (BMI z -score β_adjusted = 0.26; 95% CI: –0.19, 0.72) but lower scores in girls (BMI z -score β_adjusted = –0.41; 95% CI: –0.87, –0.05) at 7 years of age ( p _interaction = 0.04). In addition, child’s serum BDE-153 concentration (log₁₀), but not other pentaBDE congeners, demonstrated inverse associations with BMI at age 7 years (BMI z -score β_adjusted = –1.15; 95% CI: –1.53, –0.77), but there was no interaction by sex.

Conclusions: We estimated sex-specific associations with maternal PBDE levels during pregnancy and BMI at 7 years of age, finding positive associations in boys and negative associations in girls. Children’s serum BDE-153 concentrations were inversely associated with BMI at 7 years with no difference by sex. Future studies should examine the longitudinal trends in obesity with PBDE exposure and changes in hormonal environment as children transition through puberty, as well as evaluate the potential for reverse causality.