Association of ambient air pollutants with maternal thyroid hormones during the entire pregnancy

This study aims to investigate associations between PM₁₀, PM_2.5, and NO₂ and maternal thyroid hormones. We investigated 443 pregnant women in Zhejiang, China with repeated examinations of serum thyroid hormones at 10, 17, and 32 weeks. Individual exposures to ambient air pollution were retrospectively calculated by inverse distance weighting interpolation. Multivariate linear mixed models were applied to estimate the association between air pollutants and thyroid hormones. PM₁₀ exposure was positively associated with TSH (β: 0.077 [95% CI: 0.003, 0.152]), and negatively associated with FT₃ (β: -0.041 [-0.057, -0.025]) and FT₄ (β: -0.036 [-0.055, -0.017]) during the 0-90 lag days (per IQR). Similarly, increased exposure to PM_2.5 was associated with decreased FT₃ (β: -0.016 [-0.032, -0.001]), and increased Tg (β: 0.147 [0.025, 0.269]). Evaluated NO₂ levels were associated with decreased FT₃ (β: -0.026 [-0.039, -0.014]) and FT₄ (β: -0.036 [-0.052, -0.020]), as well as increased Tg (β: 0.129 [0.011, 0.247]). The results indicate that exposure to ambient PM₁₀, PM_2.5, and NO₂ throughout the entire pregnancy adversely affects thyroid hormones, implying potential health implications of air pollution on maternal thyroid function.