Cervical cap versus diaphragm for contraception.

Abstract

The cervical cap and the diaphragm are vaginal barrier contraceptive methods that prevent pregnancy by covering the cervix. The two devices also act as a reservoir for spermicide. The cervical cap is smaller and can remain in place longer than the diaphragm. Two types of cervical caps, the Prentif cap and the FemCap, have been compared to the diaphragm in randomized controlled trials. The review seeks to evaluate the contraceptive efficacy, safety, discontinuation, and acceptability of the cervical cap with that of the diaphragm. We searched MEDLINE, Popline, Cochrane Controlled Trials Register, EMBASE, and LILACS for randomized controlled trials of cervical caps, and we reviewed the references of the included publications. Also, we wrote to the manufacturers and known investigators to request information about any other published or unpublished trials not found in our search. All randomized controlled trials in any language comparing a cervical cap with a diaphragm were eligible for inclusion. All titles and abstracts located in the literature searches were assessed, and articles identified for inclusion were independently abstracted by two reviewers. Data were entered and analyzed with RevMan 4.1, and a second reviewer verified the data entered. Outcome measures include contraceptive efficacy, safety, discontinuation, and acceptability. Outcomes were calculated as Peto odds ratios with 95 percent confidence intervals using women as the denominators. Life-table and Kaplan-Meier cumulative rate ratios for selected measures were also presented in "Additional Tables." The Prentif cap was comparable to the diaphragm in preventing pregnancy, but the FemCap was not as effective in preventing pregnancy as its comparison diaphragm. The curves for the life-table cumulative pregnancy rates through 24 months for the Prentif cap and the diaphragm were not statistically significantly different (p-value of 0.39). However, the six-month Kaplan-Meier cumulative pregnancy rates for the FemCap and the diaphragm did not meet the a priori definition of clinical equivalence. The Prentif cap had a higher proportion of Class I to Class III cervical cytologic conversions at the three-month visit than the diaphragm; the odds ratio was 2.3 (95% CI, 1.0-5.1). The FemCap trial did not find differences in Papanicolaou smear results between the cap and diaphragm groups. Prentif cap users had a lower odds ratio of vaginal ulcerations or lacerations (0.3; 95% CI, 0.1-0.7) than diaphragm users. FemCap users had a higher odds ratio of blood in the device on removal (2.3; 95% CI, 1.3-4.1), but a lower odds ratio of urinary tract infections (0.6; 95% CI, 0.4-1.0) than those in the diaphragm group. In the FemCap trial, similar proportions of women reported liking their assigned device "somewhat" or "a lot" at the two-week interview. However, FemCap users were less likely than the diaphragm users to state that they were "probably" or "definitely" likely to use the device alone after completing the trial (odds ratio of 0.5; 95% CI, 0.3-0.7) or that they would recommend it to a friend (odds ratio of 0.5; 95% CI, 0.3-0.8). The Prentif cap was as effective as its comparison diaphragm in preventing pregnancy, but the FemCap was not. Both cervical caps appear to be medically safe.