Relationship between ambient air pollution and preterm birth: a retrospective birth cohort study in Yan'an, China

Preterm birth (PTB) has been associated with exposure to air pollution, but it is unclear whether effects might vary among air pollution sources in a valley city, and yet few studies have investigated refined susceptible windows for PTB. We performed a retrospective birth cohort study in Yan' an city, a typical valley city in the west of China, and analyze the effects of air pollutants on premature delivery, identify critical windows for maternal air pollutants exposure and PTB. The pregnant women who gave birth in the Affiliated Hospital of Yan'an University and Yan'an people's Hospital from January 1, 2018 to December 31, 2019 were selected as the research objects. A questionnaire survey and medical records were conducted. The daily average concentrations of particulate matter with aerodynamic diameters of <= 2.5 mu m (PM2.5) and <= 10 mu m (PM10), nitrogen dioxide (NO2), sulfur dioxide (SO2) and ozone (O-3) in Yan'an City from January 1, 2017 to December 31, 2019 were collected. After controlling the confounding factors of PTB by logistic regression model, the effect of air pollutants on preterm birth was analyzed. After controlling the confounding factors such as maternal age, gestational times and gestational hypertension syndrome, PTB was associated with exposure to third trimester PM10 (adjusted odds ratio [aOR] = 1.019, 95% confidence interval [95%CI] =1.004-1.035). PTB risk increased with second trimester exposure to SO2 (aOR = 1.039, CI = 1.011-1.068), also with third trimester (aOR = 1.031, CI = 1.010-1.053). PTB was also associated with third trimester O-3 (aOR = 1.023, CI =1.005-1.041). This study indicates that maternal exposure to PM10, SO2 and O-3 might lead to increased risk of PTB, and critical exposure windows were inconsistent.