title: Maternal cigarette smoking and the risk of pregnancy-induced hypertension and eclampsia.
abstract: BACKGROUND
  Although previous studies have found that maternal smoking decreases the risk of pregnancy-induced hypertension (PIH), the difference of this effect between primiparous and multiparous women has not been well studied and the results of the exposure-response relationships between maternal smoking and PIH are inconsistent. No previous study has specifically examined the relationship between maternal smoking and eclampsia.
  
  
  METHODS
  We analysed data from a population-based retrospective cohort study of 3 153 944 singleton pregnancies in the US. The data were derived from the national linked birth/infant mortality database for 1998. Multiple logistic regressions were used to describe the relationship between cigarette smoking and PIH and eclampsia.
  
  
  RESULTS
  The adjusted odds ratios (ORs) [95% confidence intervals (95% CIs)] for PIH were 0.80 (0.77-0.83) for primiparous women and 0.81 (0.78-0.83) for multiparous women among smokers compared with non-smokers. The corresponding adjusted ORs (95% CIs) for eclampsia were 0.74 (0.66-0.82) and 0.75 (0.68-0.83), respectively. For PIH, the adjusted OR (95% CI) for smokers vs non-smokers were 0.82 (0.79-0.86), 0.81 (0.78-0.83), 0.80 (0.77-0.83), and 0.88 (0.79-0.98), respectively, for 1-5, 6-10, 11-20, and >20 cigarettes per day (test for trend: P = 0.86). The corresponding figures for eclampsia were 0.85 (0.75-0.95), 0.74 (0.66-0.82), 0.68 (0.58-0.78), and 0.73 (0.49-1.04), respectively (test for trend: P = 0.02).
  
  
  CONCLUSIONS
  Maternal cigarette smoking decreases the risk of PIH and eclampsia, with a significant inverse exposure-response relationship apparent for eclampsia.
authors.affiliation: OMNI Research Group, Department of Obstetrics and Gynecology, University of Ottawa, Faculty of Medicine, Ontario, Canada. qyang@ohri.ca
authors.forename: Qiuying
authors.initials: Q
authors.lastname: Yang
authors.forename: Shi Wu
authors.initials: SW
authors.lastname: Wen
authors.forename: Graeme N
authors.initials: GN
authors.lastname: Smith
authors.forename: Yue
authors.initials: Y
authors.lastname: Chen
authors.forename: Daniel
authors.initials: D
authors.lastname: Krewski
authors.forename: Xi Kuan
authors.initials: XK
authors.lastname: Chen
authors.forename: Mark C
authors.initials: MC
authors.lastname: Walker
mesh_terms: D000293:Adolescent; D000328:Adult; D017677:Age Distribution; D004461:Eclampsia / Q000453:epidemiology* / Q000517:prevention & control; D004812:Epidemiologic Methods; D005260:Female; D006801:Humans; D046110:Hypertension, Pregnancy-Induced / Q000453:epidemiology* / Q000517:prevention & control; D008297:Male; D010298:Parity; D011247:Pregnancy; D012907:Smoking / Q000453:epidemiology*; D014481:United States / Q000453:epidemiology