The impact of prenatal exposure to fine particulate matter and its components on maternal and neonatal thyroid function and birth weight: a prospective cohort study

Maternal and child health has garnered considerable attention recently. The effects of prenatal exposure to PM2.5 and its components on thyroid function in both mothers and fetuses, as well as on offspring birth weight, remain unexplored. This study involved 446 mother-infant pairs from a cohort study in Ma'anshan, China, during 2021-2022. Air pollution data were obtained from the Tracking Air Pollution (TAP) project. Thyroid hormone levels (FT3, FT4, and TSH) were measured in maternal blood samples taken at various pregnancy stages and in cord blood. We employed multiple analytical methods to evaluate the effects of PM2.5 and its components on maternal thyroid function and birth weight z-score (BWz). The GLR analysis reveals that the effect of PM2.5 and its components on BWz differs according to the pregnancy stage and the specific pollutant involved. During the late pregnancy, increased exposure to PM2.5 and specific components (for instance, NO3_ and SO42-) was correlated with elevated maternal FT4 levels (p < 0.05) and reduced BWz (p < 0.05). QgC results illustrated a notable negative correlation between heightened PM2.5 exposure and BWz in late pregnancy. BKMR analysis confirmed that overall exposure to PM2.5 and its components negatively impacted BWz during the third trimester. Mediation analysis showed that changes in maternal FT4 levels accounted for approximately 8.52%, 8.05%, and 8.13% of the negative effects on BWz from exposure to NH4+, NO3_ and SO42-, respectively (p < 0.05). In healthy pregnancies, exposure to PM2.5 and its components during the late pregnancy is linked to alterations in maternal thyroid hormone levels, potentially leading to reduced birth weight. Maternal FT4 levels may mediate the connection between PM2.5 components exposure and reduced the weight of offspring.