Diaphragm and cervical cap effectiveness

Dear Alice,

How effective is the diaphragm? I was on the pill, but it made me ill and depressed. However, I miss the spontaneity and reliability of it. What about the cervical cap?

Just Say No to Hormones

Dear Just Say No to Hormones,

It’s common for people to try a few different methods of birth control before finding one that fits their lifestyle and has few, if any, undesirable side effects. The good news is that, for people with vaginas, both cervical caps and diaphragms can provide effective alternatives for pregnancy prevention without the use of hormones. The effectiveness rates of diaphragms range from 88 to 94 percent, while cervical cap effectiveness rates range from 71 to 86 percent (more on this in a bit). Both barrier methods of contraception work by physically blocking sperm from entering the cervical opening, thereby preventing it from reaching and fertilizing an egg. The diaphragm is the larger of the two methods (though designed to fit comfortably in the vagina) and is shaped like a shallow dome or cup. The cervical cap, on the other hand, is a bit smaller and looks more like a small sailor hat. Since they’re designed to be used with spermicidal jelly or creams, both methods act in two different ways — physical and chemical. Curious to know if one of these methods may be a fit for you? Keep on reading!

To effectively prevent unintended pregnancies, it’s key to use a diaphragm or cervical cap correctly and consistently each time you have sex. Diaphragms are effective around 94 percent of the time with perfect use. However, since nobody is perfect, diaphragms are effective closer to 88 percent of the time. Comparatively, cervical caps tend to be less effective, as their effectiveness rate varies depending on if a user has ever given birth vaginally. For users who have given birth, it’s effective 71 percent of the time since the cap doesn’t fit as well since the vagina and cervix are stretched during birth. However, for users who haven’t given birth, the cap is effective closer to 86 percent of the time. That said, neither diaphragms nor cervical caps are effective at protecting against sexually transmitted infections (STIs). Thus, in addition to these methods, it's strongly advised that you consider utilizing dental dams, internal (female) condoms, or external (male) condoms to reduce your risk for STI transmission.

Even though diaphragms and cervical caps are two different contraceptive methods, they happen to have a lot in common. Here are a few points to know that may affect your ability to access these methods and their effectiveness at pregnancy prevention: 

  • To get a proper fit, both methods require a visit to your health care provider for a fitting. During this fitting, your health care provider typically teaches you how to insert and remove the method of your choice. It may also be helpful to practice putting it in and taking it out a few times before you leave the office, so you can ask for any needed clarification or advice. If you experience significant weight gain or loss, pregnancy, vaginal birth, miscarriage, or abortion after 14 weeks of pregnancy, your provider will need to refit your cap or diaphragm since any of these situations can cause the fit to change. Additionally, they'll need to write a prescription for either method if you decide it's for you.
  • Both can ‘budge’ out of place during vigorous sexual activity. Specifically, if you have sex where there’s a lot of hard or fast thrusting, both a diaphragm and cervical cap can get bumped around and moved out of place. This can lead to some discomfort and reduce the effectiveness of the method.
  • They can be damaged by oil-based lubricants and vaginal medications. Direct contact with hand lotions, petroleum jelly, or vaginal medications (for yeast infections, bacterial vaginosis, etc.) can wear down diaphragms and cervical caps because these substances can degrade the material, rendering them less effective.
  • Both options are used with spermicidal jellies or creams and inserted before sex. Before sex, spermicide needs to be applied on the inside the diaphragm and on both sides of the cervical cap. Once inserted, both devices must be left in place for at least six hours after sex; the diaphragm can stay in for up to 24 hours, and the cervical cap can stay for up to 48 hours. Leaving either in for a longer than indicated may increase the risk for toxic shock syndrome (TSS). If you have sex for a second time and plan on using a diaphragm, it's best to add more spermicide before the next round to restore its effectiveness. Some people can also experience irritation when using spermicide, which may increase the risk for urinary tract infections (UTIs) and HIV. If you’re sensitive to spermicide or have previously experienced irritation from using it, diaphragms and cervical caps may not be the best choice for you.

Additionally, if you’re thinking about using diaphragms or cervical caps, it’s also worth considering if you have any known allergies or sensitivities to latex. If you do have a latex allergy, be sure to ask about a non-latex version of the contraceptive of your choice. In the United States, diaphragms are non-latex, but cervical caps are available in both latex and silicone versions.

Lastly, since you switched contraception because of your experiences with the pill’s side effects, it’s helpful to maintain an open dialogue with your health care provider about any side effects that you may experience with any birth control method. Likewise, if you’re simply considering any non-hormonal contraceptive that’s effective at pregnancy prevention, you may also wish to talk with your health care provider about non-hormonal (copper) intrauterine devices (IUDs) and contraceptive sponges (these contain spermicide, so these may not be agreeable for those who are allergic or sensitive). Together, you can discuss which non-hormonal method is most reliable, allows for spontaneity, and best suits your needs. If you still want more information about alternative contraceptive methods and safer sex, consider checking out the Go Ask Alice! Sexual and Reproductive Health archives or speaking with a health promotion specialist.

Here's to hoping you can finally find the contraceptive that's right for you!

Last updated Mar 05, 2021
Originally published Mar 08, 1995

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