Tehran University of Medical Sciences Journal of Air Pollution and Health 2476-3071 11 3 2026 09 13 377 394 Shayan Khoddam Islamic Azad University Fahimeh Ramazani Tehrani Shahid Beheshti University of Medical Sciences Hasti Borgheipour Islamic Azad University Maryam Mousavi Reproductive Endocrinology Research Center, Research Institute for Endocrine Molecular Biology, Research Institute for Endocrine Sciences, Shahid Beheshti University of Medical Sciences, Tehran, Iran Hamzeh Mohammadi Department of Occupational Health and Safety Engineering, Islamic Azad University, Tehran, Iran 2025 12 14 2026 08 10 Introduction: Exposure to ambient air pollution is a critical environmental health risk, with growing evidence linking it to adverse pregnancy outcomes. However, long-term data from Iran remain limited. This study aimed to investigate the association between maternal exposure to major air pollutants and the risk of preterm birth in Tehran.  Materials and methods: This cohort study utilized 20 years of data (2000–2020) from the Tehran Lipid and Glucose Study (TLGS). We analyzed 697 pregnancies, assessing maternal exposure to Particulate Matter (PM₂.₅, PM₁₀), Ozone (O₃), Carbon monoxide (CO), Nitrogen dioxide (NO₂), and Sulfur dioxide (SO₂) from 10 validated monitoring stations. Historical PM₂.₅ concentrations (pre-2010) were reconstructed using archival data. The association between pollutant exposure and preterm birth was analyzed using Generalized Estimating Equation (GEE) models, adjusting for maternal age and Body Mass Index (BMI). Results: The incidence of preterm birth was 3.7% (26 cases). The adjusted GEE analysis showed a positive and statistically significant association between maternal CO exposure and preterm birth (coefficient = 0.537; 95% CI: 0.158 to 0.917; P = 0.005). Conclusion: No statistically significant associations were observed for PM₂.₅, PM₁₀, NO₂, SO₂, and O₃ in the adjusted models. Our findings provide evidence suggesting a potential association between maternal exposure to ambient carbon monoxide and preterm birth in this urban population. These findings highlight the potential public health relevance of traffic-related CO exposure for pregnant women in highly polluted urban settings. https://japh.tums.ac.ir/index.php/japh/article/view/1170 https://japh.tums.ac.ir/index.php/japh/article/download/1170/480