Contraceptive effectiveness of two spermicides: A randomized trial

Objective: We conducted a multinational randomized trial to determine wheth er 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 w ho 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 st udy period. Pregnancy tests were performed on a scheduled basis. Each parti cipant was followed for 28 weeks or until she stopped considering the sperm icide as her primary method of contraception. Results: The Kaplan-Meier estimate of the C-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% po wer 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. R eported levels of sexual activity and compliance with use of the spermicide were high in both groups. Conclusion: The contraceptive effectiveness of these two spermicidal produc ts appeared similar. Both products were associated with a fairly high risk of pregnancy in this young, highly sexually active population. (Obstet Gyne col 1999;93:896-903. (C) 1999 by The American College of Obstetricians and Gynecologists.)