Brominated flame retardants (BFRs) are ubiquitous, persistent contaminants that accumulate in human tissues and pass from mother to fetus through the placenta. One class of BFRs, polybrominated diphenyl ethers (PBDEs), has a chemical structure that is very similar to endogenous thyroid hormones (THs), and numerous laboratories studies have demonstrated that PBDEs can interfere with thyroid hormone regulation through a variety of different mechanisms. Studies suggest possible relationships between maternal serum BFRs and fetal development, but results have been inconsistent. To evaluate relationships between BFRs concentrations measured in placenta, a potentially more biologically relevant measure of exposure and birth outcomes, we analyzed samples from pregnant women (n=102) from Durham, NC. Women provided serum and placenta samples which were analyzed for BFRs and birth outcome data was abstracted from medical records. In this cohort we found that BFRs, including PBDEs, accumulated to significantly higher levels in placenta associated with male infants compared to female infants, despite no differences in maternal serum levels by fetal sex. We also and found that TH levels in human placental tissues levels were associated with placenta BFRs in a sex-specific manner. We statistically evaluated associations between BFRs (serum and placenta) and continuous measures of birthweight and gestational age while adjusting for relevant covariates. Placenta BFRs were associated with lower birthweight and shorter gestation, particularly among female infants. Baby girls with the highest BDE-153 exposures, for example, were born 1.5 weeks earlier (95% confidence interval: -2.6, -0.3) than those with low levels of BDE-153 in placenta. Associations between serum BFRs and birth outcomes followed similar patterns but were generally weaker. This research has significant implications for understanding the full impact of contaminant exposures on placenta function and fetal development.
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