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.
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.
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.
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.
ClinicalTrials.gov, www.clinicaltrials.gov, NCT00335257.
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.
From the ZEG, Berlin Center for Epidemiology and Health Research, Berlin, Germany.
Supported by an unconditional grant from Bayer Schering Pharma, Berlin.
The authors thank Marlene Schoofs for editorial support in preparing the manuscript.
Corresponding author: Jürgen Dinger, ZEG, Berlin Center for Epidemiology and Health Research, Invalidenstrasse 115, 10115 Berlin, Germany; e-mail: email@example.com.
Financial Disclosure Dr. Dinger consults with manufacturers of products discussed in this article and received support for travel to the study's Safety Monitoring and Advisory Council Meetings from Bayer Schering Pharma. Ms. Bardenheuer received support for travel to the study's Safety Monitoring and Advisory Council Meetings from Bayer Schering Pharma. The other authors did not disclose any potential conflicts of interest.