title: Effects of socioeconomic position and clinical risk factors on spontaneous and iatrogenic preterm birth.
abstract: BACKGROUND
  The literature shows a variable and inconsistent relationship between socioeconomic position and preterm birth. We examined risk factors for spontaneous and iatrogenic preterm birth, with a focus on socioeconomic position and clinical risk factors, in order to explain the observed inconsistency.
  
  
  METHODS
  We carried out a retrospective population-based cohort study of all singleton deliveries in Nova Scotia from 1988 to 2003. Data were obtained from the Nova Scotia Atlee Perinatal Database and the federal income tax T1 Family Files. Separate logistic models were used to quantify the association between socioeconomic position, clinical risk factors and spontaneous preterm birth and iatrogenic preterm birth.
  
  
  RESULTS
  The study population included 132,714 singleton deliveries and the rate of preterm birth was 5.5%. Preterm birth rates were significantly higher among the women in the lowest (versus the highest) family income group for spontaneous (rate ratio 1.14, 95% confidence interval (CI) 1.03, 1.25) but not iatrogenic preterm birth (rate ratio 0.95, 95% CI 0.75, 1.19). Adjustment for maternal characteristics attenuated the family income-spontaneous preterm birth relationship but strengthened the relationship with iatrogenic preterm birth. Clinical risk factors such as hypertension were differentially associated with spontaneous (rate ratio 3.92, 95% CI 3.47, 4.44) and iatrogenic preterm (rate ratio 14.1, 95% CI 11.4, 17.4) but factors such as diabetes mellitus were not (rate ratio 4.38, 95% CI 3.21, 5.99 for spontaneous and 4.02, 95% CI 2.07, 7.80 for iatrogenic preterm birth).
  
  
  CONCLUSIONS
  Socioeconomic position and clinical risk factors have different effects on spontaneous and iatrogenic preterm. Recent temporal increases in iatrogenic preterm birth appear to be responsible for the inconsistent relationship between socioeconomic position and preterm birth.
authors.affiliation: Department of Obstetrics and Gynaecology and the School of Population and Public Health, University of British Columbia and the Children's and Women's Hospital of British Columbia, 4500 Oak Street, Vancouver, British Columbia V6H 3 N1, Canada. KSJoseph@cfri.ca.
authors.forename: K S
authors.initials: KS
authors.lastname: Joseph
authors.forename: John
authors.initials: J
authors.lastname: Fahey
authors.forename: Ketan
authors.initials: K
authors.lastname: Shankardass
authors.forename: Victoria M
authors.initials: VM
authors.lastname: Allen
authors.forename: Patricia
authors.initials: P
authors.lastname: O'Campo
authors.forename: Linda
authors.initials: L
authors.lastname: Dodds
authors.forename: Robert M
authors.initials: RM
authors.lastname: Liston
authors.forename: Alexander C
authors.initials: AC
authors.lastname: Allen
mesh_terms: D000328:Adult; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D007049:Iatrogenic Disease / Q000191:economics / Q000453:epidemiology*; D015994:Incidence; D009674:Nova Scotia / Q000453:epidemiology; D011159:Population Surveillance; D011247:Pregnancy; D047928:Premature Birth / Q000191:economics / Q000453:epidemiology / Q000209:etiology*; D012189:Retrospective Studies; D018570:Risk Assessment / Q000379:methods*; D012307:Risk Factors; D012923:Social Class; D012959:Socioeconomic Factors; D055815:Young Adult