title: Maternal smoking predicts the risk of spontaneous abortion.
abstract: BACKGROUND
  Few studies have examined smoking prior to pregnancy and the occurrence of spontaneous abortion, as most studies have addressed the risk of spontaneous abortion in relation to smoking during pregnancy. However, results are not entirely consistent. The aim of the present study was to assess the risk of spontaneous abortion considering smoking prior to pregnancy.
  
  
  METHODS
  We performed a nested case-control study using prospective data from a population-based cohort comprising 11,088 women aged 20-29 years. From this cohort, women who experienced either a spontaneous abortion (n=343) or who gave birth (n=1,578) during follow-up were selected. Associations between self-reported smoking at enrollment and subsequent spontaneous abortion were analyzed by means of multiple logistic regression.
  
  
  RESULTS
  The risk of spontaneous abortion in relation to pre-pregnancy smoking showed a clear dose-response effect. The adjusted odds ratio (95% confidence interval) for spontaneous abortion among current smokers prior to conception was 1.20 (1.04-1.39) per every extra five cigarettes smoked per day. The increased risk was only present for current smokers. The duration of smoking prior to pregnancy was not a significant predictor for subsequent spontaneous abortion.
  
  
  CONCLUSIONS
  The amount of daily smoking prior to pregnancy seems to be associated with an increased risk of spontaneous abortion, whereas the duration of smoking does not seem to be related to an increased risk of spontaneous abortion.
authors.affiliation: Department of Virus, Hormones and Cancer, Institute of Cancer Epidemiology, Danish Cancer Society, Copenhagen, Denmark.
authors.forename: Ann
authors.initials: A
authors.lastname: Nielsen
authors.forename: Charlotte Gerd
authors.initials: CG
authors.lastname: Hannibal
authors.forename: Bodil Eriksen
authors.initials: BE
authors.lastname: Lindekilde
authors.forename: Janne
authors.initials: J
authors.lastname: Tolstrup
authors.forename: Kirsten
authors.initials: K
authors.lastname: Frederiksen
authors.forename: Christian
authors.initials: C
authors.lastname: Munk
authors.forename: Thomas
authors.initials: T
authors.lastname: Bergholt
authors.forename: Lisbeth
authors.initials: L
authors.lastname: Buss
authors.forename: Bent
authors.initials: B
authors.lastname: Ottesen
authors.forename: Morten
authors.initials: M
authors.lastname: Grønbaek
authors.forename: Susanne Krüger
authors.initials: SK
authors.lastname: Kjaer
mesh_terms: D000022:Abortion, Spontaneous / Q000453:epidemiology*; D000328:Adult; D016022:Case-Control Studies; D015331:Cohort Studies; D016001:Confidence Intervals; D003718:Denmark / Q000453:epidemiology; D004305:Dose-Response Relationship, Drug; D005260:Female; D006801:Humans; D007231:Infant, Newborn; D016015:Logistic Models; D016017:Odds Ratio; D016742:Preconception Care / Q000706:statistics & numerical data; D011237:Predictive Value of Tests; D011247:Pregnancy; D011256:Pregnancy Outcome; D011446:Prospective Studies; D012307:Risk Factors; D012907:Smoking / Q000009:adverse effects*; D013997:Time Factors