title: Effectiveness of oral contraceptive pills in a large U.S. cohort comparing progestogen and regimen.
abstract: OBJECTIVE
  To estimate real-life effectiveness of oral contraceptive pills by progestogen, length of pill-free interval, and body mass index while focusing on the effect of progestogens with a long half-life and on 24-day oral contraceptive pills regimens.
  
  
  METHODS
  Outcome data from 52,218 U.S. participants in the International Active Surveillance of Women Taking Oral Contraceptives—a large, prospective, controlled, noninterventional, long-term cohort study with active surveillance of the study participants—were used to analyze contraceptive failure in association with oral contraceptive pills use. Low loss to follow-up is ensured by a comprehensive follow-up procedure. Contraceptive failure rates are described by Pearl Index and life-table analysis. Inferential statistics for contraceptive failure are based on Cox regression models.
  
  
  RESULTS
  Analyses are based on 1,634 unintended pregnancies during 73,269 woman-years of oral contraceptive pills exposure. Life-table estimates of contraceptive failure for a 24-day regimen of drospirenone and ethinyl estradiol and 21-day regimens of other progestogens were 2.1% and 3.5% after the first study year, and 4.7% and 6.7% after the third year. The adjusted hazard ratio was 0.7 (95% confidence interval 0.6–0.8). Direct comparisons of the 24-day and 21-day regimens of drospirenone and norethisterone, respectively, showed also lower contraceptive failure rates for 24-day regimens. Contraceptive failure rates adjusted for age, parity and educational level showed a slight increase with higher body mass index.
  
  
  CONCLUSIONS
  The 24-day oral contraceptive regimens containing a progestogen with a long half-life show higher contraceptive effectiveness under routine medical conditions compared with conventional 21-day regimens. Obesity seems to be associated with a slight reduction of contraceptive effectiveness.
  
  
  BACKGROUND
  ClinicalTrials.gov, www.clinicaltrials.gov, NCT00335257.
  
  
  METHODS
  II
authors.affiliation: From the ZEG, Berlin Center for Epidemiology and Health Research, Berlin, Germany.
authors.forename: Jürgen
authors.initials: J
authors.lastname: Dinger
authors.forename: Thai
authors.initials: T
authors.lastname: Do Minh
authors.forename: Nina
authors.initials: N
authors.lastname: Buttmann
authors.forename: Kristina
authors.initials: K
authors.lastname: Bardenheuer
mesh_terms: D000328:Adult; D015992:Body Mass Index; D003278:Contraceptives, Oral, Hormonal / Q000008:administration & dosage*; D005060:Europe; D005260:Female; D006801:Humans; D011247:Pregnancy; D018873:Pregnancy Rate; D011372:Progestins / Q000008:administration & dosage*; D011446:Prospective Studies; D014481:United States; D055815:Young Adult
chemical_list: D003278:Contraceptives, Oral, Hormonal; D011372:Progestins