Longer oral contraceptive regimens containing a progestogen show higher effectiveness

Compared with conventional 21-day regimens, 24-day oral contraceptive regimens containing a progestogen with a long half-life show higher contraceptive effectiveness under routine medical conditions, according to research published in the January 2011 issue of Obstetrics & Gynecology.

Jürgen Dinger, MD, PhD, and colleagues used 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 participants to analyze contraceptive failure associated with the use of oral contraceptive pills.

Analyses were based on 1,634 unintended pregnancies during 73,269 woman-years of exposure to oral contraceptive pills. Life-table estimates of contraceptive failure for a 24-day regimen of drospirenone and ethinyl estradiol (NuvaRing, Merck) and 21-day regimens of other progestogens were 2.1% and 3.5%, respectively, after the first study year and 4.7% and 6.7%, respectively, after the third year. The adjusted hazard ratio was 0.7 (95% CI, 0.6–0.8). Direct comparisons of the 24-day and 21-day regimens of drospirenone and norethisterone, respectively, also showed lower contraceptive failure rates for 24-day regimens.

Obesity seems to be associated with a slight reduction of contraceptive effectiveness, according to researchers.