Contraceptive effectiveness of two spermicides: a randomized trial

Abstract

Objective: We conducted a multinational randomized trial to determine whether a spermicidal film containing 72 mg of nonoxynol-9 per film was at least as effective in preventing pregnancy as a foaming tablet containing 100 mg of nonoxynol-9 per tablet. Methods: Between September 1995 and July 1997, 765 women aged 18–35 years who had no evidence of subfecundity were randomly assigned to use one of the two spermicides as their only contraceptive method at every coital act for 28 weeks. Participants were asked to keep coital diaries throughout the study period. Pregnancy tests were performed on a scheduled basis. Each participant was followed for 28 weeks or until she stopped considering the spermicide as her primary method of contraception. Results: The Kaplan-Meier estimate of the 6-month probability of pregnancy during typical use of the spermicide was 28.0% in the tablet group and 24.9% in the film group ( P = .78, one-tailed test). The study had nearly 75% power to have detected a difference of seven percentage points between groups. Results were almost identical when the analysis included only months when the participants reported use of the spermicide during every coital act. Reported levels of sexual activity and compliance with use of the spermicide were high in both groups. Conclusion: The contraceptive effectiveness of these two spermicidal products appeared similar. Both products were associated with a fairly high risk of pregnancy in this young, highly sexually active population.