Association between ambient PM2.5 exposure during pregnancy and risk of preterm birth: a retrospective birth cohort study in Chengdu, Southwest China.

BACKGROUND: Prenatal PM2.5 exposure has been associated with preterm birth (PTB), but evidence on exposure windows and population heterogeneity remain inconsistent. METHODS: This retrospective cohort included 35,136 singleton births at a Chengdu hospital from 2015 to 2024. Satellite- and monitor-based PM2.5 exposures were estimated for conventional and fixed gestational windows. Logistic regression adjusted for individual characteristics, meteorological factors, conception season, and district fixed effects, with cluster-robust standard errors by district and last-menstrual-period year-month. PTB was classified as earlier (28-33 weeks) or late (34-36 weeks), and exploratory subgroup analyses were conducted. RESULTS: Among 35,136 births, 2,622 (7.46%) were preterm. Mean whole-pregnancy PM2.5 concentrations were 49.11 ug/m3 for satellite data and 51.92 ug/m3 for monitoring data. Per 10 ug/m3 increase, the whole-pregnancy ORs were 1.089 (95% CI: 1.010-1.174) and 1.091 (95% CI: 0.996-1.195), respectively. Positive associations were observed during the first and third trimesters. For exposure during weeks 32-33, the ORs for late PTB were 1.063 and 1.069 using monitoring and satellite data, respectively; corresponding ORs for exposure during weeks 34-35 and PTB at week 36 were 1.084 and 1.095. Positive estimates occurred for late but not earlier PTB. Exploratory analyses suggested potential heterogeneity by ethnicity, parity, and migrant status. CONCLUSION: Prenatal PM2.5 exposure was associated with PTB,with positive associations observed for the first and third trimesters and in the landmark analyses of weeks 32-33 and 34-35. Satellite and monitoring data yielded similar district-level estimates, while satellite data provided complete coverage and narrower confidence intervals. Reducing PM2.5 exposure throughout pregnancy may help reduce PTB burden.