title: Reproduction and the risk of multiple sclerosis.
abstract: BACKGROUND
  The incidence of multiple sclerosis (MS) in Denmark has doubled in women since 1970, whereas it has been almost unchanged in men.
  
  
  OBJECTIVE
  To investigate whether age at first childbirth and number of births have an effect on the risk of developing MS.
  
  
  METHODS
  The cohort consisted of 1403 patients with MS of both sexes, identified through the Danish Multiple Sclerosis Registry, with clinical onset between 2000 and 2004. For each case, 25 control persons were drawn by random from the Danish Civil Registration System matched by sex, year of birth, and residential municipality.
  
  
  RESULTS
  More female cases than controls had no childbirths or fewer births before clinical onset (p=0.018) but only in the last five years preceding onset (p<0.0001). Childbirths within five years before clinical onset reduced the risk of MS onset in women: OR=0.54 (95% CI 0.41-0.70, p<0.0001) for one child and OR=0.68 (95% CI 0.53-0.87, p=0.002) for more than one child. Parental age at first childbirth had no effect on the risk of MS.
  
  
  CONCLUSIONS
  The data did not suggest reversed causality between childbirth and MS.
authors.affiliation: Department of Neurology, University of Copenhagen, Copenhagen, Denmark.
authors.forename: Melinda
authors.initials: M
authors.lastname: Magyari
authors.forename: Nils
authors.initials: N
authors.lastname: Koch-Henriksen
authors.forename: Claudia C
authors.initials: CC
authors.lastname: Pfleger
authors.forename: Per Soelberg
authors.initials: PS
authors.lastname: Sørensen
mesh_terms: D000328:Adult; D017668:Age of Onset; D016022:Case-Control Studies; D015984:Causality; D015331:Cohort Studies; D003718:Denmark / Q000453:epidemiology; D005260:Female; D006801:Humans; D015994:Incidence; D008297:Male; D009103:Multiple Sclerosis / Q000453:epidemiology*; D016017:Odds Ratio; D010290:Parents; D011247:Pregnancy; D012042:Registries; D012098:Reproduction; D012306:Risk; D012307:Risk Factors; D012737:Sex Factors; D055815:Young Adult
keywords: Multiple sclerosis; case-control studies; epidemiology; pregnancy; registries; risk factors