Ambient air pollutants in the first trimester of pregnancy and birth defects: an observational study

Objectives: As current studies on the relationships between air pollutants exposure during the first trimester and birth defects were not fully elucidated, this study aimed to assess the association between selected air pollutants and birth defects.

Design: An observational study.

Participants: We obtained 70 854 singletons with gestational age <20 weeks who were delivered at a large maternal and child healthcare centre in Wuhan, China.

Outcome measures: Birth defects data and daily average concentration of ambient particulate matter ≤10 µm diameter (PM₁₀), PM ≤2.5 µm diameter (PM_2.5), sulfur dioxide (SO₂) and nitrogen dioxide (NO₂) were obtained. Logistic regression analysis was applied to assess the association between maternal air pollutants exposure during first trimester and total birth defects, congenital heart defects (CHDs), limb defects and orofacial clefts with adjustments of potential covariates.

Results: There were a total of 1352 birth defect cases included in this study, with a prevalence of 19.08‰. Maternal exposed to high concentrations of PM₁₀, PM_2.5, NO₂ and SO₂ in the first trimester were significantly associated with elevated ORs of birth defects (ORs ranged from 1.13 to 1.23). Additionally, for male fetuses, maternal exposed to high PM_2.5 concentration was associated with an elevated odd of CHDs (OR 1.27, 95% CI 1.06 to 1.52). In the cold season, the ORs of birth defects were significantly increased among women exposed to PM_2.5 (OR 1.64, 95% CI 1.41 to 1.91), NO₂ (OR 1.22, 95% CI 1.08 to 1.38) and SO₂ (OR 1.26, 95% CI 1.07 to 1.47).

Conclusions: This study showed unfavourable effects of air pollutants exposure during the first trimester on birth defects. Especially, the association between maternal PM_2.5 exposure and CHDs was only observed among male fetuses, and stronger effects of PM_2.5, NO₂ and SO₂ exposure on birth defects were observed in the cold season.