Gestational exposure to ambient particulate matter and preterm birth: An updated systematic review and meta-analysis.

Previous studies on gestational particulate matter (PM) exposure and preterm birth (PTB) showed inconsistent results, and no study systematically examined the short-term effect of PM exposure on PTB subtypes. To investigate both long- and short-term effects of the evidence to date in general population, we searched for epidemiological studies on PM exposure and PTB that published in PubMed, Web of Science, Embase and Cochrane Library up to March 31, 2022. The protocol for this review was registered with PROSPERO (CRD42021265202). Heterogeneity was assessed by Cochran's Q test and I statistic. Publication bias was evaluated using funnel plots and Egger's tests. Subgroup analysis, meta-regression and sensitivity analysis were performed. Of 16,801 records, 84 eligible studies were finally included. The meta-analysis of long-term effect showed that per 10 μg/m increase in PM and PM during entire pregnancy were associated with PTB, the pooled odds ratios (ORs) were 1.084 (95% CI: 1.055-1.113) and 1.034 (95% CI: 1.018-1.049). Positive associations were found between PM in second trimester and PTB subtypes. For the short-term exposure, we observed that PTB was positively associated with a 10 μg/m increment in PM on lag day 2 and 3, the pooled ORs and 95% CIs were 1.003 (1.001-1.004) and 1.003 (1.001-1.005), with I of 65.30% and 76.60%. PM exposure on ave day 1 increased the risk of PTB, the pooled OR was 1.001 (95% CI: 1.000, 1.001). We also found that PM exposure in 2 weeks prior to birth increased PTB risk. Our results support the hypothesis of both long- and short-term PM exposure increase the risk of PTB. Further well-designed longitudinal studies and investigations into potential biological mechanisms are warranted.