Association of maternal serum concentration of hydroxylated polychlorinated biphenyls with maternal and neonatal thyroid hormones: The Hokkaido birth cohort study.

BACKGROUND:Evidence on the toxicity of hydroxylated metabolites of polychlorinated biphenyls (OH-PCBs) for thyroid hormones (TH) is limited, and the underlying mechanism remains unknown. OBJECTIVES:We aimed to investigate the effects of environmental prenatal exposure to OH-PCBs and maternal and neonatal TH levels, taking the maternal-fetal TH transfer into account. METHODS:In this prospective birth cohort (the "Hokkaido study") we included 222 mother-neonate pairs. We measured five OH-PCB isomers in maternal serum samples either during pregnancy or within 5 days of delivery. Thyroid stimulating hormone (TSH) and free thyroxine (FT4) levels were obtained from maternal blood samples at an early gestational stage (median; 11.1 weeks) and from heel prick samples of neonates between 4 and 7 days after birth. Multiple linear regression analysis and structural equation modeling (SEM) were performed to investigate the associations between maternal OH-PCB and maternal and neonatal TH levels. RESULTS:Median concentration of ∑OH-PCBs was 25.37 pg/g wet weight. The predominant isomer was 4-OH-CB187, followed by 4-OH-CB146+3-OH-CB153. In the fully adjusted linear regression analysis, maternal ∑OH-PCBs was positively associated with maternal FT4, and 4-OH-CB187 was positively associated with both maternal and neonatal FT4 levels. Maternal OH-PCBs showed no significant association with TSH among mothers and neonates. Path analysis indicated the indirect pathway from 4-OH-CB187 exposure to increased neonatal FT4, via maternal THs and neonatal TSH. CONCLUSIONS:These findings suggest that maternal exposure to OH-PCBs during pregnancy may increase both maternal and neonatal FT4 levels. Neonatal FT4 is presumed to be increased by prenatal 4-OH-CB187 indirectly, and this process may be mediated by maternal THs and neonatal TSH.