title: Area-level poverty and preterm birth risk: a population-based multilevel analysis.
abstract: BACKGROUND
  Preterm birth is a complex disease with etiologic influences from a variety of social, environmental, hormonal, genetic, and other factors. The purpose of this study was to utilize a large population-based birth registry to estimate the independent effect of county-level poverty on preterm birth risk. To accomplish this, we used a multilevel logistic regression approach to account for multiple co-existent individual-level variables and county-level poverty rate.
  
  
  METHODS
  Population-based study utilizing Missouri's birth certificate database (1989-1997). We conducted a multilevel logistic regression analysis to estimate the effect of county-level poverty on PTB risk. Of 634,994 births nested within 115 counties in Missouri, two levels were considered. Individual-level variables included demographics factors, prenatal care, health-related behavioral risk factors, and medical risk factors. The area-level variable included the percentage of the population within each county living below the poverty line (US census data, 1990). Counties were divided into quartiles of poverty; the first quartile (lowest rate of poverty) was the reference group.
  
  
  RESULTS
  PTB < 35 weeks occurred in 24,490 pregnancies (3.9%). The rate of PTB < 35 weeks was 2.8% in counties within the lowest quartile of poverty and increased through the 4th quartile (4.9%), p < 0.0001. High county-level poverty was significantly associated with PTB risk. PTB risk (< 35 weeks) was increased for women who resided in counties within the highest quartile of poverty, adjusted odds ratio (adj OR) 1.18 (95% CI 1.03, 1.35), with a similar effect at earlier gestational ages (< 32 weeks), adj OR 1.27 (95% CI 1.06, 1.52).
  
  
  CONCLUSIONS
  Women residing in socioeconomically deprived areas are at increased risk of preterm birth, above other underlying risk factors. Although the risk increase is modest, it affects a large number of pregnancies.
authors.affiliation: Department of Obstetrics and Gynecology, Washington University School of Medicine, St, Louis, Missouri, USA. defranee@ucmail.uc.edu
authors.forename: Emily A
authors.initials: EA
authors.lastname: DeFranco
authors.forename: Min
authors.initials: M
authors.lastname: Lian
authors.forename: Louis A
authors.initials: LA
authors.lastname: Muglia
authors.forename: Mario
authors.initials: M
authors.lastname: Schootman
mesh_terms: D005260:Female; D005843:Geography; D005865:Gestational Age; D006801:Humans; D016015:Logistic Models; D008923:Missouri / Q000453:epidemiology; D016017:Odds Ratio; D011203:Poverty / Q000706:statistics & numerical data; D011247:Pregnancy; D011256:Pregnancy Outcome / Q000191:economics*; D047928:Premature Birth / Q000453:epidemiology*; D012307:Risk Factors; D012959:Socioeconomic Factors; D016387:Women's Health
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