Perfluoroalkyl and polyfluroalkyl substances and maternal thyroid hormones in early pregnancy

The development of the embryo and fetal brain depends on maternal transfer of thyroid hormones (THs) in early pregnancy. Perfluoroalkyl and polyfluoralkyl substances (PFAS) may disrupt maternal TH homeostasis in pregnancy, but findings from epidemiologic studies were inconsistent. We aimed to assess this relationship in early pregnancy in a large prospective cohort study.

A total of 1885 pregnant women enrolled in the Shanghai Birth Cohort were used. Ten PFAS, free thyroxine (FT4), free triiodothyronine (FT3), thyroid stimulating hormone (TSH) and thyroid peroxidase antibody (TPOAb) were measured in maternal blood collected prior to 16 weeks of gestation. Multiple linear regression accompanied by restricted cubic spline was used to examine the association and the exposure-response relationship between each PFAS and TH in separate models. Possible effect modification by TPOAb status was also investigated.

Perfluorooctanoic acid [PFOA, β = 0.121, 95% confidence interval (CI): 0.015, 0.227] and perfluorohexane sulfonate (PFHxS, β = 0.123, 95% CI: 0.024, 0.222) were positively associated with FT4. Perfluorononanoic acid (PFNA, β = 0.179, 95% CI: 0.047, 0.311) and PFHxS (β = 0.197, 95% CI: 0.054, 0.339) were positively associated with FT3, while PFHxS was negatively associated with TSH (β = -0.115, 95%CI: 0.216, -0.014). TPOAb-positivity appeared to modify the associations between PFAS and THs. In TPOAb-positive women, several long-chain PFAS were positively associated with FT4 and/or FT3 and tended to be negatively associated with TSH.

Several long-chain PFAS were associated with disrupted TH homeostasis in Chinese pregnant women, especially among TPOAb-positive women.