Relationship between environmental PM2.5 exposure in early pregnancy and thyroid hormone levels in pregnant women

Objectives: To investigate a potential association between exposure to different concentrations of environmental fine particulate matter (PM2.5) during early pregnancy and maternal thyroid hormone levels. Methods: The Midong District of Urumqi City was selected as the site for PM2.5 exposure, while Bole City served as the non-exposed group. Participants were women volunteers enrolled before the 28th week of gestation. Basic data were collected, and levels of FT3, FT4, TSH, and urinary iodine were measured. Generalized linear models were used to investigate associations between different environmental exposures to PM2.5 and maternal thyroid hormone levels in early pregnancy. A restricted cubic spline was employed to examine exposure-response relationships between PM2.5 pollution and maternal thyroid hormone levels. Results: The mean daily indoor, outdoor, and multi-environmental PM2.5 exposure of pregnant women in early pregnancy was significantly different between the two sites (p < 0.05). The average daily exposure concentrations of PM2.5 in different environments during the first weeks of pregnancy in the two regions were negatively correlated with maternal levels of FT3 and FT4. The risk of abnormal thyroid hormone levels was higher in pregnant women living in the Midong District compared to those from Bole City. Conclusions: PM2.5 exposure during early pregnancy was associated with decreased maternal levels of FT3 and FT4. The adverse health effects of exposure to PM2.5 during early pregnancy on both pregnant women and their offspring should be continually emphasized.