title: The influence of prior oral contraceptive use on risk of endometriosis is conditional on parity.
abstract: OBJECTIVE
  To estimate the influence of prior oral contraceptive pill (OCP) use on future diagnosis of endometriosis in young women.
  
  
  METHODS
  Prospective cohort study, the Australian Longitudinal Study on Women's Health.
  
  
  METHODS
  Community-based sample.
  
  
  METHODS
  9,585 women age 18-23 at study onset.
  
  
  METHODS
  None.
  
  
  METHODS
  Risk of self-reported endometriosis estimated with Cox proportional-hazards regression with time-dependent covariates.
  
  
  RESULTS
  Compared with never users, endometriosis hazard ratios in nulliparous women with <5 years and ≥ 5 years of OCP use (preceding diagnosis) were 1.8 (95% CI, 1.30-2.53) and 2.3 (95% CI, 1.59-3.40), respectively. Similar risk was seen in both women reporting infertility and unsure fertility. In parous women with <5 years of use, the hazard ratio for endometriosis was 0.41 (95% CI, 0.15-0.56) and for ≥ 5 years of use was 0.45 (95% CI, 0.16-1.23). Women reporting early noncontraceptive OCP use had a twofold higher risk (odds ratio 2.07; 95% CI, 1.72-2.51).
  
  
  CONCLUSIONS
  Prior OCP exposure reduces the risk of diagnosis of endometriosis in parous women but increases it among nulliparous women; these associations appear unaffected by fertility status. An increased risk of endometriosis diagnosis seen in women reporting early noncontraceptive OCP use may explain some of the positive OCP risk seen in nulliparous women.
authors.affiliation: Department of Obstetrics and Gynecology, Chicago, Illinois; Department of Obstetrics and Gynecology, University of Chicago, Pritzker School of Medicine, Chicago, Illinois. Electronic address: ftu@northshore.org.
authors.forename: Frank F
authors.initials: FF
authors.lastname: Tu
authors.affiliation: Center for Biomedical Research Informatics, NorthShore University HealthSystem, Chicago, Illinois.
authors.forename: Hongyan
authors.initials: H
authors.lastname: Du
authors.affiliation: Department of Obstetrics and Gynecology, Chicago, Illinois.
authors.forename: Gregory P
authors.initials: GP
authors.lastname: Goldstein
authors.affiliation: Department of Medical Social Sciences, Northwestern University School of Medicine, Chicago, Illinois.
authors.forename: Jennifer L
authors.initials: JL
authors.lastname: Beaumont
authors.affiliation: Center for Biomedical Research Informatics, NorthShore University HealthSystem, Chicago, Illinois.
authors.forename: Ying
authors.initials: Y
authors.lastname: Zhou
authors.affiliation: School of Human Movement Studies, University of Queensland, St. Lucia, Queensland, Australia.
authors.forename: Wendy J
authors.initials: WJ
authors.lastname: Brown
mesh_terms: D000293:Adolescent; D001315:Australia; D016009:Chi-Square Distribution; D003278:Contraceptives, Oral, Hormonal / Q000009:adverse effects*; D004715:Endometriosis / Q000175:diagnosis / Q000209:etiology* / Q000503:physiopathology / Q000517:prevention & control; D005260:Female; D005298:Fertility; D006801:Humans; D008137:Longitudinal Studies; D015999:Multivariate Analysis; D010298:Parity; D011247:Pregnancy; D016016:Proportional Hazards Models; D011446:Prospective Studies; D012307:Risk Factors; D057566:Self Report; D013997:Time Factors; D055815:Young Adult
chemical_list: D003278:Contraceptives, Oral, Hormonal
keywords: Combined oral contraceptives; dysmenorrhea; endometriosis; risk factor