title: The risk of unintended pregnancies in users of the contraceptive patch compared to users of oral contraceptives in the UK General Practice Research Database.
abstract: BACKGROUND
  The transdermal contraceptive patch EVRA has been marketed since 2002 as an alternative to oral contraceptives (OCs), but large follow-up studies of effectiveness are lacking.
  
  
  METHODS
  We used a cohort plus a nested case-control study to estimate rates and hazard ratios of unintended pregnancy among users of different hormonal contraceptives (HC) and to evaluate the effects of various potential predictors on unintended pregnancy.
  
  
  RESULTS
  Rates of unintended pregnancy were all low (overall rate 0.17 per 100 women-years), though they were slightly higher in users of progestogen-only OCs and EVRA compared to users of second-generation OCs. The hazard ratios for unintended pregnancy were also higher for users of progestogen-only OCs and the patch compared to users of second-generation OCs, although these estimates may be confounded by compliance. Rates of unintended pregnancy were inversely associated with age and duration of HC use as well as with other predictors of pregnancy but not body mass index or use of antibiotics.
  
  
  CONCLUSIONS
  The rates of unintended pregnancy were low for all study HCs, and while the data on unintended pregnancy in EVRA users compared to OC users are sufficient to rule out major differences in the rate of unintended pregnancy, they are not sufficient to rule out modest ones.
authors.affiliation: Boston Collaborative Drug Surveillance Program, Boston University School of Medicine, Lexington, MA 02421, USA. sjick@bu.edu
authors.forename: Susan S
authors.initials: SS
authors.lastname: Jick
authors.forename: Katrina W
authors.initials: KW
authors.lastname: Hagberg
authors.forename: James A
authors.initials: JA
authors.lastname: Kaye
authors.forename: Hershel
authors.initials: H
authors.lastname: Jick
mesh_terms: D000279:Administration, Cutaneous; D000293:Adolescent; D000328:Adult; D016022:Case-Control Studies; D003277:Contraceptives, Oral, Combined; D016208:Databases, Factual; D004338:Drug Combinations; D004997:Ethinyl Estradiol / Q000008:administration & dosage*; D019304:Ethinyl Estradiol-Norgestrel Combination; D005260:Female; D006801:Humans; D009644:Norgestrel / Q000008:administration & dosage / Q000031:analogs & derivatives*; D011247:Pregnancy; D011275:Pregnancy, Unwanted; D016016:Proportional Hazards Models; D006113:United Kingdom; D055815:Young Adult
chemical_list: D003277:Contraceptives, Oral, Combined; D004338:Drug Combinations; C511292:Ortho Evra; D009644:Norgestrel; D004997:Ethinyl Estradiol; D019304:Ethinyl Estradiol-Norgestrel Combination