Association Between Air Pollutant Exposure and Preterm Birth: A Retrospective Cohort Study.

Abstract

OBJECTIVES: To explore the relationship between air pollutant exposure and preterm birth. DESIGN: It was a retrospective cohort study. METHODS: We conducted a retrospective cohort study of 48,534 singleton pregnancies delivered at Nantong Maternal and Child Healthcare Hospital between January 1, 2017 and December 31, 2022. Daily concentrations of six pollutants (PM2.5, PM10, SO2, NO2, CO, O3) were assigned to each woman’s residence and averaged over the first (T1), second (T2), and third (T3) trimesters. Cox proportional hazards models estimated hazard ratios (HRs) and 95% confidence intervals (CIs) for PTB across pollutant quartiles, adjusting for maternal age, parity, season of last menstrual period, fetal sex, pregnancy complications, heart disease, uterine fibroids, obesity, and precious infant status. Generalized estimating equations (GEE) accounted for within-subject exposure correlations. Sensitivity analyses compared models with and without adjustment for pregnancy complications. RESULTS: In fully adjusted Cox models, highest-quartile exposure to PM2.5 during T1 and T3 was associated with increased PTB risk (T1 Q4 vs. Q1: HR=1.155, 95% CI: 1.025–1.302; T3 Q4 vs. Q1: HR=1.325, 95% CI: 1.182–1.486). SO2, NO2, and O3 exposures in T3 similarly elevated PTB risk (SO2 Q4 vs. Q1: HR=1.750, 95% CI: 1.570–1.951; NO₂ Q4 vs. Q1: HR=1.311, 95% CI: 1.154–1.489; O₃ Q4 vs. Q1: HR=1.466, 95% CI: 1.282–1.677). GEE analyses corroborated these associations (all p<0.001). Sensitivity analyses yielded consistent estimates, indicating negligible mediation by pregnancy complications. CONCLUSIONS: Late-pregnancy exposure to pollutants confers the risk for preterm birth. Public health interventions should prioritize air quality improvement during the third trimester to reduce PTB incidence.