A reanalysis of data from two clinical studies--in which 1,439 women were randomly assigned to use either the contraceptive sponge or the diaphragm and 1,394 women were randomly assigned to use either the cervical cap or the diaphragm--found first-year probabilities of failure during typical use of 17% for the sponge, 18% for the cervical cap and 13-17% for the diaphragm. The first-year probabilities of failure during perfect use are 11-12% for the sponge, 10-13% for the cervical cap and 4-8% for the diaphragm. The probability of failure during perfect use is significantly higher among women who have given birth than among those who have not for users of the sponge (19-21% vs. 9-10%) and users of the cervical cap (26-27% vs. 8-10%), but not for users of the diaphragm.
PIP: An important prerequisite of informed contraceptive choice is access to accurate information about the efficacy of various methods. Knowledge about the efficacy of female barrier methods is particularly scarce, however, even though such methods are currently being used by approximately 2.4 million women in the US. The authors present this paper with the objectives of shedding light upon the efficacy of female barrier methods when used correctly and consistently, and whether failure rates for the methods are higher among women who have had children than among women who have not. Findings are based upon the reanalysis of data from two clinical studies conducted in the US during the 1980s. One study randomly assigned 1439 women from 13 clinics to use either the contraceptive sponge or the diaphragm, while the other study randomly assigned 1394 women in Los Angeles, San Diego, and San Francisco to use either the cervical cap or the diaphragm. First-year probabilities of failure during typical use were 17% for the sponge, 18% for the cervical cap, and 13-17% for the diaphragm. First-year probabilities of failure during perfect use are 11-12% for the sponge, 10-13% for the cervical cap, and 4-8% for the diaphragm. Further, the probability of failure during perfect use was determined to be significantly higher among women who have given birth than among those who have not for users of the sponge (19-21% versus 9-10%) and users of the cervical cap (26-27% versus 8-10%), but not for users of the diaphragm.