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 PM_2.5 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 PM_2.5 and its components on maternal thyroid function and birth weight z-score (BWz). The GLR analysis reveals that the effect of PM_2.5 and its components on BWz differs according to the pregnancy stage and the specific pollutant involved. During the late pregnancy, increased exposure to PM_2.5 and specific components (for instance, \({\text{NO}}_{3}^{\_} { }\) ${\text{NO}}_3^{\_}$ and \({\text{SO}}_{4}^{2 - }\) ${\text{SO}}_4^{2-}$ ) 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 PM_2.5 exposure and BWz in late pregnancy. BKMR analysis confirmed that overall exposure to PM_2.5 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 \({\text{NH}}_{4}^{ + }\) ${\text{NH}}_4^{+}$ , \({\text{NO}}_{3}^{\_}\) ${\text{NO}}_3^{\_}$ and \({\text{SO}}_{4}^{2 - }\) ${\text{SO}}_4^{2-}$ , respectively (p < 0.05). In healthy pregnancies, exposure to PM_2.5 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 PM_2.5 components exposure and reduced the weight of offspring.