Prenatal exposure to PM_2.5 components and the risk of different types of preterm birth and the mediating effect of pregnancy complications: a cohort study

Objectives: This study aims to reveal the single and mixed associations of PM_2.5 and its components with very, moderately, and late preterm births and to explore the potential mediating role of pregnancy complications in PM_2.5-induced preterm birth.

Study design: This was a retrospective cohort study.

Methods: We enrolled 168,852 mothers and matched the concentrations of PM_2.5 and its five components (OM, SO₄^2-, BC, NO₃^-, and NH₄⁺) based on their geographical location. Next, we used generalized linear models, quantile g-computation, and mediation analysis to evaluate the associations of PM_2.5 and its components with very, moderately, and late preterm births and the mediating role of pregnancy complications.

Results: Prenatal exposure to PM_2.5 and its components was associated with preterm birth, and the association was strongest in the third trimester. Preterm birth was associated with co-exposure to a mixture of PM_2.5 components in the third trimester, and the contributions of NO₃^-, NH₄⁺, and BC to the risk of preterm birth were positive. Meanwhile, pregnancy complications mediated PM_2.5-induced preterm birth. Moreover, very and moderately preterm births were associated with PM_2.5 and its components in the second and third trimesters, and very and late preterm births were associated with co-exposure to a mixture of PM_2.5 components in the third trimester.

Conclusions: Later exposure to PM_2.5 during pregnancy will cause earlier preterm birth. Targeted and positive interventions for anthropogenic sources of specific PM_2.5 components and pregnancy complications are helpful for preterm birth prevention.