Impact of Polybrominated Diphenyl Ethers on Thyroid Hormone Levels Among California Women During Second Trimester of Pregnancy

Abstract

S-31C4-5 Background/Aims: In animal studies, polybrominated diphenyl ether (PBDE) flame retardants are linked to hypothyroidism, characterized by reduced free and total thyroxine (T4) levels. However, associations between PBDEs and thyroid hormone levels in humans have been inconsistent. We examined the association between PBDEs and thyroid hormone levels during the second trimester of pregnancy among women in California, where exposures are expected to be elevated due to the state's unique furniture flammability standard (TB117). Methods: Serum samples were collected from 25 pregnant women (gestational age: 19–23 weeks) at San Francisco General Hospital between 2008 and 2009. Eighteen samples to date were analyzed for 19 tri- to deca-substituted PBDE congeners. A summary measure of 4 frequently detected congeners (47, 99, 100, and 153) was also constructed (ΣPBDEs). Samples were analyzed for thyroid-stimulating hormone (TSH), and free and total T4. Analysis of polychlorinated biphenyls and perfluorinated compounds are underway. Results: The study population was 36% Hispanic, 40% Black, 12% White, and 12% Asian. The majority of patients used public insurance. Mean age was 23 years (range: 16–42 years). PBDE levels among this study population (geometric mean; BDE-47: 45 ng/g lipid, ΣPBDEs: 81 ng/g lipid) were elevated compared to pregnant women in National Health and Nutrition Examination Survey 2003–2004 (n = 75) (geometric mean; BDE-47: 24 ng/g lipid, ΣPBDEs: 54 ng/g lipid). Serum BDE-47 was inversely associated with free T4 (R2 = 0.26, P = 0.02) and positively associated with TSH (R2 = 0.14, P = 0.07). Associations remained unchanged after adjusting for race, age, or gestational age. Similar associations were observed for ΣPBDEs, BDE-99, and BDE-100 but not BDE-153. Conclusion: PBDEs are associated with decreased T4 and increased TSH among pregnant women. These effects are consistent with findings from animal studies, and warrant further investigation since maternal subclinical hypothyroidism during pregnancy has important implications for fetal development. The elevated PBDE exposures are also consistent with higher use of flame retardants in California.