Associations of ambient air pollution exposure during pregnancy with maternal and neonatal thyroid function: Systematic review and meta-analysis.

Thyroid function in both pregnant women and newborns is vital for ensuring healthy child growth and development. Existing evidence suggests that exposure to air pollutants during pregnancy may disrupt maternal and neonatal thyroid function; however, findings across studies remain inconsistent. This systematic review and meta-analysis included 24 studies (55,814 pregnant women and 84,645 neonates) published until April 30, 2025. Results indicated that each 10 μg/m3 increase in PM2.5 was associated with a significant decrease in maternal FT4 levels (-0.42%; 95% CI: -0.83%, -0.01%) and neonatal FT4 levels (-0.90%; 95% CI: -1.52%, -0.29%). PM2.5 exposure also increased the risk of maternal hypothyroxinemia (OR = 1.49; 95% CI: 1.16, 1.91). Subgroup analyses revealed stronger effects in the first and third trimesters. Additionally, the study found a nonlinear relationship between PM2.5 exposure and thyroid hormone levels in pregnant women while potential breakpoints vary across thyroid parameters, which range from 20.60 to 71.02 μg/m3, the collective patterns indicate that the most dynamic PM2.5-related effects on maternal thyroid function occur within the 20-60 μg/m3 exposure window. Above approximately 60 μg/m3, response slopes generally diminish, reflecting a sublinear curvature in the exposure-response relationships. These breakpoints notably exceed the World Health Organization air quality guideline (10 μg/m3). These findings underscore the need for stricter air quality regulations to protect maternal and neonatal thyroid health. Further research is warranted to explore the underlying mechanisms and identify critical exposure windows.