Umbilical cord serum perfluoroalkyl substance mixtures in relation to thyroid function of newborns: Findings from Sheyang Mini Birth Cohort Study

The epidemiological evidence on the associations between prenatal exposure to perfluoroalkyl substances (PFAS) and thyroid hormones in newborns was inconclusive. We aimed to estimate associations of fetal exposure to PFAS individually and in mixtures with thyroid function of newborns. A total of 490 mother-newborn pairs were included from Sheyang Mini Birth Cohort Study (SMBCS), a prospective cohort that recruited between June 2009 and January 2010. 12 PFAS and 7 thyroid function indicators were quantified in umbilical cord serum. We examined associations of prenatal exposure to individual and a mixture of PFAS with thyroid function indicators using multivariable linear regression and weighted quantile sum (WQS) regression models with adjustment for potential confounders, respectively. Higher cord serum concentrations of PFAS mixtures were related to increases in TT4 and FT4 levels, and reductions in TSH concentrations of newborns. Combining single-chemical models with multiple-chemical models, PFOS, PFNA and PFUnDA were associated with increased TT4 levels with contributing to the mixture effects of 46.4%, 22.8%, and 16.7%, respectively. PFOS exposure was in positive association with cord serum FT4 concentrations and contributed 28.9% to the joint effects of mixtures. PFNA and PFHpA were the most important contributors to the decreases of TSH levels of newborns with 46.3% and 45.0% among the mixtures, respectively. The current findings indicated the thyroid disruption of individual PFAS and their mixtures in cord serum. Additional studies are warranted to explore the underlying biological mechanisms, particularly for PFAS mixtures.