Air pollution and adverse birth outcomes: a narrative review of epidemiological and mechanistic findings

Abstract Air pollution remains a significant global health challenge and is increasingly recognized as a critical exposomic risk factor for adverse birth outcomes. Although numerous epidemiological studies have linked prenatal air pollution exposure to low birth weight, preterm birth, and stillbirth, important uncertainties remain regarding the underlying biological mechanisms, critical exposure windows, and the interplay between different pollutants and susceptibility factors. This narrative review synthesizes epidemiological findings and mechanistic evidence identified through literature searches in PubMed, Scopus, and Web of Science to provide a comprehensive overview of how maternal exposure to air pollutants affects fetal development and pregnancy outcomes. The reviewed epidemiological evidence largely supports an association between maternal air pollution exposure and adverse birth outcomes. For example, a 10 µg/m 3 increase in fine particulate matter (PM 2.5 ) exposure during the second trimester has been associated with an 11.8 g reduction in birth weight and a 23.1% increase in the risk of preterm birth. Oxidative stress, inflammation, endocrine disruption, vascular dysfunction, and epigenetic modifications are considered key biological pathways through which air pollution may impair placental function, alter fetal growth trajectories, and increase the likelihood of pregnancy complications. The placenta serves as a critical interface between maternal and fetal health and is particularly vulnerable to environmental insults, with air pollution exposure linked to changes in placental morphology, perfusion, and metabolic function. However, challenges persist in disentangling the effects of individual pollutants, establishing causality, identifying critical windows of susceptibility, and determining the extent to which sociodemographic, lifestyle, and genetic factors modify these associations. Current research gaps underscore the need for studies integrating high-resolution exposure assessment, multi-pollutant modeling, and mechanistic investigations to better clarify the impact of air pollution on pregnancy outcomes. Graphical Abstract Air pollution and adverse birth outcomes