Pregnancy exposure to organophosphate flame retardants and alterations in maternal and newborn thyroid hormone levels

The recent tightening of regulations on the polybrominated diphenyl ethers (PBDEs) production has led to an increase in the use of organophosphate flame retardants (OPFR). Although several toxicological studies suggest that these chemicals can disrupt thyroid homeostasis, epidemiological studies remain sparse. This work aims to investigate the associations between prenatal OPFR exposure and thyroid hormone levels in mothers and their newborns. The study population consisted of 442 mother-child pairs from the French SEPAGES cohort recruited between 2014 and 2017. Four OPFR metabolites -diphenyl phosphate (DPhP), di-n-butyl phosphate (DNBP), bis(1,3-dichloro-2-propyl) phosphate (BDCIPP), and bis(2-butoxyethyl) phosphate (BBOEP) -were measured in two pools of multiple urine samples collected during the second and third trimesters of pregnancy. Thyroid hormones were measured in maternal sera at the second trimester, and in newborns from a heel-prick blood spot. Adjusted linear regression models were used to assess the associations between each OPFR metabolite and each thyroid hormone. Maternal urinary iodine, child's sex, and exposure window were considered in additional analyses as potential effect modifiers. DNBP and BDCIPP were positively associated with newborn total thyroxine (TT4) and tended to be negatively associated with maternal total triiodothyronine (TT3). DPhP concentrations were also negatively associated with maternal thyroid stimulating hormone (TSH) levels. Our results suggest that exposure to OPFR could influence thyroid hormone levels in pregnant women and their newborns, raising concerns about potential adverse impacts on fetal development and postnatal health.