Modifying effects of prenatal exposure to rare earth elements on birth outcomes through maternal thyroid function in early pregnancy.

The potential health effects of exposure to rare earth elements (REEs) remain largely unexplored. This prospective cohort study aimed to elucidate the association between early pregnancy REE exposure and maternal thyroid function, as well as neonatal birth outcomes, in a cohort of pregnant women in Beijing, China. Additionally, the study explored the mediating role of thyroid homeostasis in the effects of REE exposure. Serum concentrations of fifteen REEs, along with Free Thyroxine (FT4), Thyroid Stimulating Hormone (TSH), and Thyroid Peroxidase Antibodies (TPOAb), were measured in 195 pregnant women. Multivariable linear regression analyses identified significant correlations between REE exposure and disruptions in maternal thyroid homeostasis. Specifically, Praseodymium (Pr) and Lutetium (Lu) were positively associated with FT4 levels, while Gadolinium (Gd) showed a positive correlation with TSH levels. Conversely, Thulium (Tm) was negatively associated with FT4 levels, and Yttrium (Y) was negatively correlated with TSH levels, indicating distinct interactions of specific REEs with thyroid regulation. Notably, Lu remained positively correlated with FT4 levels (β = 1.39, 95% CI = 0.55, 2.22) after adjusting for multiple comparisons. Regarding neonatal birth outcomes, Dysprosium (Dy) was found to be negatively associated with infant birth weight (β = -0.09, 95% CI = -0.170, -0.002). Furthermore, gender-specific analyses revealed significant associations between REE exposure and TPOAb levels among female neonates. Mediation analyses indicated that TSH significantly mediated the relationships between Terbium (Tb) and Y exposure and neonatal birth outcomes. The study suggests that REEs may disrupt endocrine function, particularly thyroid hormones, which could adversely affect neonatal growth, highlighting the need for further research on their impact in vulnerable populations.