The association between air pollution and temperature with risk of preterm neonatal mortality in Iran: a distributed lag time series model

Preterm delivery remains a significant determinant of neonatal morbidity and mortality worldwide. In this retrospective cohort study, we investigated the relationship between air pollutants, temperature, and preterm neonatal mortality in Tehran from 2008 to 2019 using time series analysis. Air pollution monitoring data spanning a 10-year study period were collected from various areas of Tehran through the Air Quality Control Center. Neonatal mortality data related to preterm births were obtained from the National Statistics Office of Iran, with mortality records registered at Tehran's main cemetery during the same period. We employed distributed lag linear and non-linear models to explore associations. Air pollutants (PM2.5, PM10, CO, O3, NO2, SO2) and the Air Quality Index (AQI) were assessed for their impact on preterm neonatal mortality. Additionally, we examined the effect of temperature using distributed lag models, considering both immediate and longer-term effects. Among 6494 preterm neonatal deaths during the study period, no statistically significant relationships were observed between air pollutants and preterm neonatal mortality. However, temperature exhibited a strong effect. Cold temperatures were associated with increased mortality risk, particularly at lag 2-5 and longer lags. Interestingly, a protective effect was observed at lag 0. Our results emphasize the need to consider temperature fluctuations in preterm neonatal health outcomes, even when air pollutants do not directly correlate with mortality.