Examining the Evidence
Focus on Contraception: Cervical cap versus diaphragm: Efficacy and acceptability
To evaluate the efficacy, safety, discontinuation, and acceptability of the cervical cap in comparison with the diaphragm.
Methods and Results
Investigators searched the literature for randomized controlled trials comparing the cervical cap to the diaphragm. Two trials met inclusion criteria; both recruited sexually active women aged 18 to 40 years. The first trial randomized subjects to the Prentif Cavity Rim Cervical Cap (Lamberts Ltd, Oxford, England) or the Ortho diaphragm (Ortho Pharmaceutical, Raritan, NJ). The second compared the FemCap cervical cap (FemCap Inc, Del Mar, Calif) with the All-Flex diaphragm (Ortho). Outcomes were calculated as Peto odds ratios with 95% confidence intervals (CI), using total number of women as the denominator. Life-table and Kaplan-Meier cumulative rate ratios were also calculated for selected measures.
As a contraceptive, the Prentif Cap was comparable in efficacy to the diaphragm, but the FemCap was less effective than its comparison diaphragm.
The Prentif Cap had a higher proportion of class I to class III (older classification of Papanicolaou smears) cervical cytologic conversions at 3 months than the diaphragm, with an odds ratio of 2.3 (95% CI, 1.0-5.1); there were no differences in Pap smear results between groups in the FemCap trial. Prentif Cap users had a lower odds ratio of vaginal ulcerations or lacerations (0.3; 95% CI, 0.1-0.7) than diaphragm users, and FemCap users had a higher odds ratio of blood in the device on removal (2.3; 95% CI, 1.3-4.1). FemCap users also had a lower odds ratio of urinary tract infections than women using the diaphragm (0.6; 95% CI, 0.4-1.0).
Few women use the cervical cap as their primary contraceptive, although it has been available since the late 1980s. Concerns about efficacy, frequent office visits, and limited sexual spontaneity likely contribute to its relatively low popularity. Further, residency training programs tend to focus on hormonal contraception.
Unfortunately, despite its comprehensive and detailed database review, this metaanalysis is of limited value, since only 2 studies were deemed worthy of inclusion. Other concerns include:
- Unacceptable dropout rates. Only 34% of women assigned to the Prentif Cap completed the study. The FemCap group had a similar but slightly lower rate of discontinuation. These dropout rates contribute negatively to any predetermined significance.
- Different follow up durations. For the Prentif Cap, investigators calculated the cumulative life-table rate ratios of pregnancy in comparison with the diaphragm for periods ranging from 6 months to 2 years. (At 6 months, it was 1.3.) In the FemCap trial, the Kaplan-Meier 6-month cumulative pregnancy rate in comparison with the diaphragm was 1.7, but the FemCap’s efficacy beyond that time was not established.
- Incomparable groups for cytologic review. As the authors discuss, the cervical cap has been implicated in the progression of cytologic abnormalities on Pap smears. Further, it does not protect women from sexually transmitted infections such as human papil-lomavirus, so the risk of developing subsequent cytologic abnormalities exists.
- The difficulty of determining acceptability. Accurate estimates of acceptability are difficult to formulate, although the high dropout rate in both trials suggests limited popularity. Interestingly, 31% of FemCap users experienced dislodgement of the device and a significant number had difficulty with removal, yet there was a lower dropout rate than among Prentif Cap users.
Both the diaphragm and cervical cap provide acceptable levels of birth control, but should be recommended primarily to women unable to utilize more effective methods and those who have infrequent intercourse. Frequent office visits may be required to ensure proper use, ascertain rates of discontinuation, and assess for Pap smear abnormalities.