Impacts of extreme air pollution events on pregnancy outcomes: A systematic review

Extreme air pollution events are characterised by high pollution concentrations and a wide impact range, which may pose a serious threat to the health of pregnant women and fetuses. Air pollutants can affect fetal development through the placental barrier, increasing the risk of premature birth, low birth weight, gestational hypertension and miscarriage. Although some studies have investigated the impact of extreme air pollution events on pregnancy outcomes, there is no systematic and comprehensive synthesis of the evidence regarding the impact of these extreme events.

Given the frequent occurrence of extreme air pollution events due to climate change and intensified human activities, this systematic literature review aims to assess the impact of extreme air pollution events on adverse pregnancy outcomes.

The final literature search was conducted on March 24, 2026, using Scopus, Web of Science and PubMed databases. The search was limited to the English language and publication dates from January 1, 2015 to March 1, 2026. Studies were selected using the PECOS (Pregnant women, Exposure to extreme air pollution events, Comparison with lower or no exposure, Pregnancy outcomes, Observational study designs) framework and synthesised following Synthesis Without Meta-Analysis (SWiM) guidelines. From an initial pool of 5187 results, 30 studies met the inclusion criteria and were included in the final synthesis. Risk of bias was assessed using the Liverpool Literature Risk of Bias Assessment Tool.

This review found that exposure to certain extreme air pollution events during pregnancy was consistently associated with increased risks of preterm birth and low birth weight, the most obvious is wildfire-related PM_2.5:reported effect estimates ranged from no association to odds ratios of approximately 1·4-1·6 (with 95% CI) for preterm birth and from approximately 1·00 to 1·03-1·06 (with 95% CI) for low birth weight. PM_2.5 was the most studied pollutant (26 studies), followed by PM₁₀, SO₂, NO₂, CO, and O₃. The most common adverse outcomes were preterm birth (reported in 18 studies) and low birth weight (reported in 11 studies).

Despite heterogeneity in definitions and confounder adjustment, findings show that the overall direction of associations was consistent across studies, suggesting that acute extreme air pollution events pose a significant risk to maternal and fetal health.