title: Acute Impact of Hourly Ambient Air Pollution on Preterm Birth.
abstract: BACKGROUND
  Preterm birth is a major perinatal health problem, but factors leading to it are still not completely understood.
  
  
  OBJECTIVE
  Our goal was to identify the relation between acute increase in ambient air pollution in a few hours before onset of labor and the risk of preterm birth.
  
  
  METHODS
  We collected registered birth outcome data and hourly ambient air pollution measurements during 2009‒2013 in Brisbane, Australia. Using a time-stratified case-crossover design and conditional logistic regression models with natural cubic splines, we assessed the shape of air pollution-preterm birth curve, after controlling for potential confounders. We also examined the effect modification of other factors.
  
  
  RESULTS
  The association between air pollution [nitrogen dioxide (NO2), sulfur dioxide (SO2), and carbon monoxide (CO)] and preterm birth was nonlinear. Threshold concentrations for the mean of 0‒24 hr NO2, 24‒48 hr SO2, and 24‒48 hr CO before onset of labor were 7.6 parts per billion (ppb), 3.8 ppb, and 162.5 ppb, respectively. Increases in air pollution concentrations above thresholds were associated with increased risks of preterm birth. The odds ratios of preterm birth at the 95th percentile of NO2, SO2, and CO against the thresholds were 1.17 (95% CI: 1.08, 1.27), 1.01 (95% CI: 0.99, 1.04), and 1.18 (95% CI: 1.06, 1.32), respectively. The associations were modified by demographic factors, such as maternal smoking and socioeconomic status.
  
  
  CONCLUSIONS
  Acute increases in ambient air pollution concentrations above certain levels before onset of labor may stimulate preterm birth.
  
  
  BACKGROUND
  Li S, Guo Y, Williams G. 2016. Acute impact of hourly ambient air pollution on preterm birth. Environ Health Perspect 124:1623-1629; http://dx.doi.org/10.1289/EHP200.
authors.affiliation: School of Public Health, The University of Queensland, Brisbane, Queensland, Australia.
authors.forename: Shanshan
authors.initials: S
authors.lastname: Li
authors.forename: Yuming
authors.initials: Y
authors.lastname: Guo
authors.forename: Gail
authors.initials: G
authors.lastname: Williams