title: Recent use of oral contraceptives and the risk of multiple sclerosis.
abstract: BACKGROUND
  Exogenous estrogens affect the onset and clinical course of experimental allergic encephalomyelitis. Oral contraceptives, a frequent source of exogenous estrogens in humans, could have a role in the development of multiple sclerosis (MS).
  
  
  OBJECTIVE
  To examine whether recent oral contraceptive use and pregnancy history are associated with the risk of MS.
  
  
  METHODS
  A case-control study nested in the General Practice Research Database. This database contains prospective health information (drug prescriptions and clinical diagnoses) on more than 3 million Britons who are enrolled with selected general practitioners.
  
  
  METHODS
  One hundred six female incident cases of MS, younger than 50 years, with at least 3 years of continuous recording in the General Practice Research Database before the date of first symptoms (index date), identified between January 1, 1993, and December 31, 2000, and 1001 controls matched on age, practice, and date of joining the practice. Main Outcome Measure Incidence of first symptoms of MS, confirmed through medical records.
  
  
  RESULTS
  The incidence of MS was 40% lower (odds ratio, 0.6; 95% confidence interval, 0.4-1.0) in oral contraceptive users compared with nonusers during the previous 3 years. The risk of MS increased in the 6 months after pregnancy (odds ratio, 2.9, 95% confidence interval, 1.2-6.6), but it was not otherwise related to parity.
  
  
  CONCLUSIONS
  The hormonal changes that occur during oral contraceptive use and pregnancy may be associated with a short-term reduction in the risk of MS, and the postpartum period may be associated with a short-term increase in the risk of MS.
authors.affiliation: Department of Epidemiology, Harvard School of Public Health, Brigham and Women's Hospital, Boston, MA 02115, USA. aalogut@alumni.unav.es
authors.forename: Alvaro
authors.initials: A
authors.lastname: Alonso
authors.forename: Susan S
authors.initials: SS
authors.lastname: Jick
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Olek
authors.forename: Alberto
authors.initials: A
authors.lastname: Ascherio
authors.forename: Hershel
authors.initials: H
authors.lastname: Jick
authors.forename: Miguel A
authors.initials: MA
authors.lastname: Hernán
mesh_terms: D000293:Adolescent; D000328:Adult; D000367:Age Factors; D016022:Case-Control Studies; D003276:Contraceptives, Oral / Q000009:adverse effects*; D005260:Female; D019538:Health Care Surveys / Q000379:methods; D006801:Humans; D008137:Longitudinal Studies; D009103:Multiple Sclerosis / Q000453:epidemiology* / Q000209:etiology*; D011247:Pregnancy; D011446:Prospective Studies; D012189:Retrospective Studies; D012306:Risk; D013997:Time Factors
chemical_list: D003276:Contraceptives, Oral