title: Offspring number, pregnancy, and risk of a first clinical demyelinating event: the AusImmune Study.
abstract: OBJECTIVE
  To examine the association between past pregnancy, offspring number, and first clinical demyelination risk.
  
  
  METHODS
  Cases (n = 282) were aged 18-59 years with a first clinical diagnosis of CNS demyelination (first clinical demyelinating event [FCD]) and resident within 1 of 4 Australian centers (from latitudes 27° south to 43° south) from 2003 to 2006. Controls (n = 542) were matched to cases on age, sex, and study region, without first clinical diagnosis of CNS demyelination.
  
  
  RESULTS
  Higher offspring number was associated with FCD risk among women (p < 0.001) but not men (p = 0.71); difference in effect; p = 0.001. Among women, higher parity was associated with reduced risk of FCD (adjusted odds ratio 0.51 [95% confidence interval 0.36, 0.72] per birth) with a similar magnitude of effect observed among classic first demyelinating events (adjusted odds ratio 0.47 [95% confidence interval 0.29, 0.74]). The apparent beneficial effect of higher parity was also evident among parous women only (p < 0.001). Among cases, a clear female excess was evident for those with low but not high (4 or more) offspring number. Factors such as human leukocyte antigen DR15 genotype did not appear to modify the association between higher parity and a reduced FCD risk among women.
  
  
  CONCLUSIONS
  These findings are consistent with a cumulative beneficial effect of pregnancy. Temporal changes toward an older maternal age of parturition and reduced offspring number may partly underlie the increasing female excess among MS cases over time.
authors.affiliation: Murdoch Childrens Research Institute, Melbourne, Australia. anne-louise.ponsonby@mcri.edu.au
authors.forename: A-L
authors.initials: AL
authors.lastname: Ponsonby
authors.forename: R M
authors.initials: RM
authors.lastname: Lucas
authors.forename: I A
authors.initials: IA
authors.lastname: van der Mei
authors.forename: K
authors.initials: K
authors.lastname: Dear
authors.forename: P C
authors.initials: PC
authors.lastname: Valery
authors.forename: M P
authors.initials: MP
authors.lastname: Pender
authors.forename: B V
authors.initials: BV
authors.lastname: Taylor
authors.forename: T J
authors.initials: TJ
authors.lastname: Kilpatrick
authors.forename: A
authors.initials: A
authors.lastname: Coulthard
authors.forename: C
authors.initials: C
authors.lastname: Chapman
authors.forename: D
authors.initials: D
authors.lastname: Williams
authors.forename: A J
authors.initials: AJ
authors.lastname: McMichael
authors.forename: T
authors.initials: T
authors.lastname: Dwyer
mesh_terms: D000022:Abortion, Spontaneous / Q000453:epidemiology; D000293:Adolescent; D000328:Adult; D001315:Australia / Q000453:epidemiology; D001327:Autoimmune Diseases / Q000453:epidemiology; D016001:Confidence Intervals; D004247:DNA / Q000235:genetics; D003627:Data Interpretation, Statistical; D003711:Demyelinating Diseases / Q000453:epidemiology* / Q000209:etiology*; D005260:Female; D005838:Genotype; D006684:HLA-DR Antigens / Q000235:genetics; D006801:Humans; D008297:Male; D008572:Menarche; D008875:Middle Aged; D016017:Odds Ratio; D010298:Parity / Q000502:physiology*; D011247:Pregnancy / Q000502:physiology*; D011248:Pregnancy Complications / Q000453:epidemiology*; D018570:Risk Assessment; D012307:Risk Factors; D012737:Sex Factors; D011795:Surveys and Questionnaires; D055815:Young Adult
chemical_list: D006684:HLA-DR Antigens; D004247:DNA