Exploring the association between air pollution and spontaneous abortion through systematic review and bibliometric analysis

Air pollution has been recognized as a significant environmental risk factor with potentially adverse effects on women's reproductive health. This study presents the existing literature on air pollution exposure and its link to spontaneous abortion (SAB) utilizing a systematic literature review (SLR) and bibliometric analysis (BA). Firstly, SLR was employed to collect relevant articles based on specified inclusion/exclusion criteria and formulated research questions. Secondly, BA was used to map and assess research trends, current knowledge, and structure using network analysis constructed on citation, co-citation, co-occurrence, and collaboration patterns among articles, authors, keywords, and institutions, respectively. Thematic analysis identified emerging and crucial research areas. This review encompasses 45 articles investigating short- and long-term exposure to single pollutants (n = 18) and multi-air pollutants (n = 27). Particulate matter-PM2.5 (n = 12 of 16) and PM10 (n = 10 of 14), and NO2 (n = 8 of 14) demonstrated the most consistent associations with SAB followed by SO2 (n = 5 of 9) and O3 (n = 3 of 6), while CO (n = 4 of 6), PAH (n = 1 of 2), BC, and heavy metal (n = 1 of 1 each) showed inconsistent associations. This study reports considerable heterogeneity between studies concerning study design, air pollution exposure assessment, and outcome assessment. Studies of this nature present immense challenges and demand a standard protocol and a multi-disciplinary strategy involving scientists, epidemiologists, governments, and policymakers. Finally, systematic mapping and analysis performed in this study provide valuable insights into future research paths, offering a roadmap for further investigation.