Maternal exposure to PM_2.5 may increase the risk of congenital hypothyroidism in the offspring: A national database based study in China

Background: Maternal exposure to air pollution is related to fetal dysplasia. However, the association between maternal exposure to air pollution and the risk of congenital hypothyroidism (CH) in the offspring is largely unknown. Methods: We conducted a national database based study in China to explore the association between these two parameters. The incidence of CH was collected from October 1, 2014 to October 1, 2015 from the Chinese Maternal and Child Health Surveillance Network. Considering that total period of pregnancy and consequently the total period of particle exposure is approximately 10 months, average exposure levels of PM_2.5, PM₁₀ and Air Quality Index (AQI) were collected from January 1, 2014 to January 1, 2015. Generalized additive model was used to evaluate the association between air pollution and the incidence of CH, and constructing receiver operating characteristic (ROC) curve was used to calculate the cut-off value. Results: The overall incidence of CH was 4.31 per 10,000 screened newborns in China from October 1, 2014 to October 1, 2015. For every increase of 1 μg/m³ in the PM_2.5 exposure during gestation could increase the risk of CH (adjusted OR = 1.016 per 1 μg/m³ change, 95% CI, 1.001-1.031). But no significant associations were found with regard to PM₁₀ (adjusted OR = 1.009, 95% CI, 0.996-1.018) or AQI (adjusted OR = 1.012, 95% CI,0.998-1.026) and the risk of CH in the offspring. The cut-off value of prenatal PM_2.5 exposure for predicting the risk of CH in the offspring was 61.165 μg/m³. Conclusions: The present study suggested that maternal exposure to PM_2.5 may exhibit a positive association with increased risk of CH in the offspring. We also proposed a cut-off value of PM_2.5 exposure that might determine reduction in the risk of CH in the offspring in highly polluted areas.