Time-to-Event Analysis of Fine Particle Air Pollution and Preterm Birth: Results from North Carolina, 2001-2005

Exposures to air pollution during pregnancy have been suggested as risk factors for preterm birth; however epidemiological evidence remains mixed and limited. This paper examines the association between ambient levels of particulate matter < 2.5 μm in aerodynamic diameter (PM2.5) and the risk of preterm birth in North Carolina between the period 2001 to 2005. The authors estimated the risks of cumulative and lagged average exposures to PM2.5 during pregnancy via a two-stage discrete-time survival model. The authors also considered exposure metrics derived from (1) ambient concentrations measured by the Air Quality System monitoring network (AQS) and (2) predicted concentrations by statistically fusing AQS with process - based numerical model output (FSD). Using the AQS measurements, an interquartile range (1.73μg/m3) increase in cumulative PM2.5 exposure was associated with a 6.8% (95% posterior interval: 0.5%, 13.6%) increase in the risk of preterm birth. Using the FSD predicted levels and accounting for prediction error, the authors also found significant adverse association between trimester 1, trimester 2, and cumulative PM2.5 exposure and preterm birth. These findings suggest that exposure to ambient PM2.5 during pregnancy is associated with increased risk of preterm birth even in aregion characterized by relatively good air quality.