How the relationships between preterm birth and ambient air pollution vary over space: A case study in Georgia, USA using geographically weighted logistic regression

Preterm birth (PTB) is a major cause of infant mortality and morbidity. The relationships between PTB and ambient air pollution have been examined by many previous studies worldwide, but the results vary among different studies, and no general conclusion could be drawn about the relationships. We analyzed 116,112 live and singleton births in year 2000 in Georgia, USA in this cross-sectional study. A spatial statistical method, Geographically Weighted Logistic Regression (GWLR), was employed to model the relationships between PTB and two ambient air pollutants, ozone (O₃) and fine particulate matter (PM_2.5), with nine individual-level birth and maternal demographic, socioeconomic, behavioral, and lifestyle factors, and three community socioeconomic status (SES) and urbanization variables as covariates. Different from the results calculated from global logistic regression, the results obtained from the GWLR model show that the relationships between PTB and the two pollutants vary over space. Positively significant (a higher risk of PTB is associated with a higher concentration of air pollutant), negatively significant (a lower risk of PTB is associated with a higher concentration of air pollutant), and non-significant relationships between PTB and air pollutants are all discovered in different regions of Georgia, and the varying relationships are strongly related to the varying SES and urbanization level of the communities of the births. PTB is not significantly associated with either O₃ or PM_2.5 in most of the state, especially in urban communities. The positively significant relationship between PTB and O₃ or PM_2.5 that indicates either air pollutant might be a significant PTB risk factor is primarily located in rural communities with low SES. These findings suggest that in order to more successfully reduce PTB risk, it is necessary to consider the varying relationships between PTB and air pollution across the communities with different levels of urbanization and SES for making and implementation of local public health policies.