title: Outdoor air pollution, preterm birth, and low birth weight: analysis of the world health organization global survey on maternal and perinatal health.
abstract: BACKGROUND
  Inhaling fine particles (particulate matter with diameter ≤ 2.5 μm; PM2.5) can induce oxidative stress and inflammation, and may contribute to onset of preterm labor and other adverse perinatal outcomes.
  
  
  OBJECTIVE
  We examined whether outdoor PM2.5 was associated with adverse birth outcomes among 22 countries in the World Health Organization Global Survey on Maternal and Perinatal Health from 2004 through 2008.
  
  
  METHODS
  Long-term average (2001-2006) estimates of outdoor PM2.5 were assigned to 50-km-radius circular buffers around each health clinic where births occurred. We used generalized estimating equations to determine associations between clinic-level PM2.5 levels and preterm birth and low birth weight at the individual level, adjusting for seasonality and potential confounders at individual, clinic, and country levels. Country-specific associations were also investigated.
  
  
  RESULTS
  Across all countries, adjusting for seasonality, PM2.5 was not associated with preterm birth, but was associated with low birth weight [odds ratio (OR) = 1.22; 95% CI: 1.07, 1.39 for fourth quartile of PM2.5 (> 20.2 μg/m3) compared with the first quartile (< 6.3 μg/m3)]. In China, the country with the largest PM2.5 range, preterm birth and low birth weight both were associated with the highest quartile of PM2.5 only, which suggests a possible threshold effect (OR = 2.54; CI: 1.42, 4.55 and OR = 1.99; CI: 1.06, 3.72 for preterm birth and low birth weight, respectively, for PM2.5 ≥ 36.5 μg/m3 compared with PM2.5 < 12.5 μg/m3).
  
  
  CONCLUSIONS
  Outdoor PM2.5 concentrations were associated with low birth weight but not preterm birth. In rapidly developing countries, such as China, the highest levels of air pollution may be of concern for both outcomes.
authors: University of South Carolina Arnold School of Public Health, Columbia, South Carolina, USA.
authors: Nancy L
authors: NL
authors: Fleischer
authors: Mario
authors: M
authors: Merialdi
authors: Aaron
authors: A
authors: van Donkelaar
authors: Felipe
authors: F
authors: Vadillo-Ortega
authors: Randall V
authors: RV
authors: Martin
authors: Ana Pilar
authors: AP
authors: Betran
authors: João Paulo
authors: JP
authors: Souza
mesh_terms: D000397:Air Pollution / Q000009:adverse effects*; D005260:Female; D006801:Humans; D007230:Infant, Low Birth Weight; D007231:Infant, Newborn; D052638:Particulate Matter / Q000633:toxicity*; D011247:Pregnancy; D047928:Premature Birth / Q000139:chemically induced / Q000453:epidemiology*; D014944:World Health Organization
chemical_list: D052638:Particulate Matter