Background: Polybrominated diphenyl ethers (PBDEs) reduce blood concentrations of thyroid hormones in laboratory animals, but it is unclear whether PBDEs disrupt thyroid hormones in pregnant women or newborn infants.

Objectives: We investigated the relationship between maternal PBDE levels and thyroid hormone concentrations in maternal and cord sera.

Methods: We used data from the Health Outcomes and Measures of the Environment (HOME) Study, a prospective birth cohort of 389 pregnant women in Cincinnati, Ohio, who were enrolled from 2003 through 2006 and delivered singleton infants. Maternal serum PBDE concentrations were measured at enrollment (16 ± 3 weeks of gestation). Thyroid hormone concentrations were measured in maternal serum at enrollment ( n = 187) and in cord serum samples ( n = 256).

Results: Median maternal serum concentrations of BDEs 28 and 47 were 1.0 and 19.1 ng/g lipid, respectively. A 10-fold increase in BDEs 28 and 47 concentrations was associated with a 0.85-μg/dL [95% confidence interval (CI): 0.05, 1.64] and 0.82-μg/dL (95% CI: 0.12, 1.51) increase in maternal total thyroxine concentrations (TT₄), respectively. Both congeners were also positively associated with maternal free thyroxine (FT₄). We also observed positive associations between BDE-47 and maternal total and free triiodothyronine (TT₃ and FT₃). A 10-fold increase in BDE-28 was associated with elevated FT₃ concentrations (β = 0.14 pg/mL; 95% CI: 0.02, 0.26). In contrast, maternal PBDE levels were not associated with thyroid hormone concentrations in cord serum.

Conclusions: These findings suggest that maternal PBDE exposure, particularly BDEs 28 and 47, are associated with maternal concentrations of T₄ and T₃ during pregnancy.