Associations of Ambient Particulate Matter with Maternal Thyroid Autoimmunity and Thyroid Function in Early Pregnancy

This prospective birth cohort study evaluated the association of exposure to PM_2.5 (diameter ≤2.5 μm), PM_1-2.5 (1-2.5 μm), and PM₁ (≤1 μm) with maternal thyroid autoimmunity and function during early pregnancy. A total of 15,664 pregnant women were included at 6 to 13⁺⁶ gestation weeks in China from 2018 to 2020. Single-pollutant models using generalized linear models (GLMs) showed that each 10 μg/m³ increase in PM_2.5 and PM_1-2.5 was related with 6% (odds ratio [OR] = 1.06, 95% confidence interval [CI]: 1.01, 1.12) and 15% (OR = 1.15, 95% CI: 1.08, 1.22) increases in the risk of thyroid autoimmunity, respectively. The odds of thyroid autoimmunity significantly increased with each interquartile range increase in PM_2.5 and PM_1-2.5 exposure (P for trend <0.001). PM₁ exposure was not significantly associated with thyroid autoimmunity. GLM with natural cubic splines demonstrated that increases in PM_2.5 and PM_1-2.5 exposure were associated with lower maternal FT4 levels, while a negative association between PM₁ and FT4 levels was found when exposure exceeded 32.13 μg/m³. Only PM_2.5 exposure was positively associated with thyrotropin (TSH) levels. Our findings suggest that high PM exposure is associated with maternal thyroid disruption during the early pregnancy.