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3243008 
Journal Article 
Effectiveness of Oral Contraceptive Pills in a Large U.S. Cohort Comparing Progestogen and Regimen 
Dinger, J; Do Minh, T; Buttmann, N; Bardenheuer, K 
2011 
1 
Obstetrics and Gynecology
ISSN: 0029-7844
EISSN: 1873-233X 
117 
1 
33-40 
WOS:000285500800006 
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. CONCLUSION: 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.