Ambient ozone exposure and pregnancy complications and adverse birth outcomes: A systematic review and meta-analysis

Background: Ambient ozone pollution is becoming a global health threat under global warming. Evidence on the association between ambient ozone and pregnancy complications and adverse birth outcomes has grown enormously. To provide a comprehensive assessment of the evidence, we performed a systematic review and metaanalysis to outline current epidemiological evidence. Methods: A systematic literature search up to January 2024 was conducted in PubMed, Web of Science, Cochrane Library and Embase. We included studies that examined the association of ambient ozone exposure with pregnancy complications and birth outcomes. Data extraction was performed independently. All eligible studies were synthesized qualitatively. A random-effects meta-analysis was used to summarize the available effect estimates that calculated with a 10 mu g/m3 exposure. We further evaluated whether geographic location, study design, study quality, and exposure assessments explain the heterogeneity. This study protocol was registered with PROSPERO (CRD42024499445). Results: A total of 10,940 records were originally searched, 65 articles were finally included. Our results showed that first trimester ozone exposure significantly increased the risk of preeclampsia (pooled odds ratio (OR) = 1.018, 95%CI: 1.006-1.030). For birth outcomes, short-term ozone exposure was associated with the risk of preterm birth, with the pooled OR of 1.005 (95%CI: 1.002-1.008) and 1.003(95%CI:1.000-1.005). First trimester and whole pregnancy ozone exposure were associated with the risk of small for gestational age, with the pooled OR of 1.007 (95%CI: 1.002-1.012) and 1.030 (95%CI: 1.010-1.050), respectively. Conclusion: First trimester ozone exposure was associated with adverse pregnancy complications and adverse birth outcomes. Future investigations that considering local climates and population characteristics are warranted to explore the vulnerability at local and regional levels for tailored preventions.