SynthesisBMC pregnancy and childbirth2026
Association between long-term and short-term exposure to outdoor air pollution and stillbirth: a systematic review and meta-analysis.
Synthesis in BMC pregnancy and childbirth, 2026. The graph could read no effect estimate from its abstract, so it casts no vote on the map. Not yet cited in PubMed.
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Abstract
This systematic review and meta-analysis aimed to investigate the relationship between both short-term and long-term exposure to key outdoor air pollutants specifically particulate matter (PM10 and PM2.5), sulfur dioxide (SO2), nitrogen dioxide (NO2), ozone (O3) and carbon monoxide (CO) and the risk of stillbirth. An extensive literature search was performed using multiple databases, including PubMed, Web of Science, Scopus, and Embase, with studies considered up to August 20, 2024. The quality of the studies was assessed using established criteria. Twenty-two studies met the inclusion criteria, highlighting significant associations between outdoor air pollutants and stillbirth. Long-term exposure to NO2/NOx during the first, second, and third trimesters was linked to increased odds of stillbirth, with standardized ORs of 2.79 (95% CI: 1.26–6.14), 2.74 (95% CI: 1.25-6.00), and 2.63 (95% CI: 1.25–5.56), respectively.However, no significant association was observed for NO2/NOx exposure throughout the entire pregnancy (OR: 2.84, 95% CI: 0.89–9.08). Similarly, each 10 µg/m3 increase in PM10 during each trimester was associated with elevated stillbirth risk, yielding standardized ORs of 2.31 (95% CI: 1.44–3.68), 2.56 (95% CI: 1.51–4.35), and 2.73, (95% CI: 1.53–4.87), respectively. Additionally, PM10 exposure throughout the entire pregnancy showed increased risk, with a standardized OR of 2.78 (95% CI: 1.34–5.76). Likewise, a 10 µg/m3 increase in PM2.5 exposure was associated with higher stillbirth risk in each trimester, resulting in ORs of 2.53 (95% CI: 1.16–5.48), 2.69 (95% CI: 1.17–6.19), and 2.75 (95% CI: 1.12–6.73), respectively. A 10 µg/m3 increase in PM2.5 exposure over the entire pregnancy was linked to increased odds of stillbirth (OR: 2.92, 95% CI: 1.4–6.06). Short-term exposure, evaluated over multiple lag days, displayed varied risk patterns, particularly regarding CO and SO2, while PM2.5 effects showed inconsistencies across studies. Due to substantial heterogeneity in lag period definitions, exposure metrics, and effect estimate formats across studies, a quantitative meta-analysis for short-term exposure was not feasible; thus, evidence for short-term effects remains descriptive and preliminary. This review suggests that outdoor air pollution is associated with an increased stillbirth risk, highlighting the need for public health measures and standardized research.
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