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Diaphragms and cervical caps are vaginal barrier methods of birth control. Each type is manually inserted into the vagina and placed over the cervix, to prevent sperm from entering the uterus and fallopian tubes.

Diaphragms and cervical caps serve the same function. They differ slightly in size and in fit. The amount of time you can leave them inserted also differs.

Diaphragms and cervical caps have similar success rates for preventing pregnancy. People who have already given birth vaginally to a full-term baby may do better with a diaphragm than with a cervical cap.

Read on to learn about the differences and similarities between these two methods of birth control.

The only cervical cap that is currently available in the United States is FemCap. FemCap is an FDA-approved medical device designed to prevent pregnancy. It comes in three sizes. You’ll need to be fitted for a cervical cap by your doctor. For that reason, it is only available by prescription.

FemCap is sized as:

  • 22 millimeters (mm): usually best for those who have never given birth
  • 26 mm: usually best for those who have been pregnant but didn’t deliver vaginally
  • 30 mm: usually best for those who have vaginally delivered a full-term baby

Cervical caps are made from silicone rubber that is hormone-free. Their shape is sometimes referred to as a thimble or sailor’s hat. They’re inserted into the vagina in the same way as tampons.

Once inserted, a cervical cap should fit snugly over your cervix. This prevents seminal fluid from entering the uterus and fallopian tubes.

To be effective, cervical caps must be used with spermicide. The cap contains a reservoir for spermicide which faces outward, toward the opening of the vagina. You’ll need to insert additional spermicide each time you have penis-in-vagina (PIV) sex.

Cervical caps can be inserted 15 minutes to 40 hours prior to having PIV sex. For the cap to be effective, you must leave it inside your body for at least 6 hours after sex. This helps ensure that the captured sperm outside the cap have time to die and can’t enter the uterus.

Cervical caps can remain in place for up to 48 hours. It has a removal strap you grip with your finger when you’re ready to remove it.

Cervical caps are reusable and typically last for about a year. You should get refitted for a new cervical cap by your gynecologist annually.

Cervical caps are one of the least effective birth control methods available. According to Planned Parenthood, the failure rate for those who have never been pregnant is in excess of 14 pregnancies per 100 people in 1 year.

Two trial studies found that FemCap did not prevent pregnancy as well as diaphragms.

People who have been pregnant and delivered full-term babies via vaginal delivery have the highest failure rate. This may be as high as 23 to 32 pregnancies out of 100 people per year.

It can be challenging to use a cervical cap perfectly. Typical use differs from perfect use and impacts the cap’s effectiveness. Things that can increase the cap’s failure rate include:

  • dislodging during sex, reducing the cap’s ability to block semen from entering the uterus
  • forgetting to reapply spermicide prior to new sexual activity
  • pulling the cap out before 6 hours have passed
  • using a damaged cap with unnoticed tears that may let sperm penetrate the cervix

Cervical caps have several advantages which may make them a viable form of birth control.

Affordability

Since the passing of the Affordable Care Act, most health insurers are required to cover all forms of birth control. Many people who use a cervical cap will be able to get the cap for free, without a copay. If you don’t have insurance, you may be able to get a free or low-cost cervical cap through state-run programs or clinics.

Hormone-free

If you only have sex occasionally or are breastfeeding, you may prefer a nonhormonal form of birth control. Cervical caps are also a viable choice for people who get side effects from other forms of birth control.

Reusable

Unlike condoms, cervical caps can be reused multiple times. This helps ensure you always have birth control on hand. You will, however, need to continue to purchase spermicide to use with your cervical cap. Spermicide is sold in drugstores and doesn’t require a prescription.

Can be inserted ahead of time

Unlike condoms, cervical caps can be discreetly inserted ahead of time, without interrupting sexual activity.

Like cervical caps, diaphragms are a reusable form of barrier birth control. They are dome-shaped and foldable. You insert a diaphragm into your vagina the same way you do a tampon. Like cervical caps, diaphragms require spermicide to be effective.

Caya and Milex are the two diaphragm brands currently available in the United States. They both work the same but are shaped and sized differently. You and your doctor can determine which type is best for you.

Caya is latex-free. It is made from silicone and nylon. Caya comes in one size that is contoured to fit most people with vaginas. According to the manufacturer, 80 percent of women can use Caya. Even though it doesn’t require a fitting, you will need a doctor’s prescription to get this diaphragm.

Milex is latex-free. It is made from silicone and has a cadmium-free, metal-spring rim. It is dome-shaped and has a wide seal. Milex comes in eight sizes. You will need to be fitted by your doctor for a Milex diaphragm. It is available for purchase with a prescription.

Diaphragms fit over the cervix and surrounding area. Once inserted, they are meant to remain lodged behind your pubic bone. Like cervical caps, they stop seminal fluid from entering the uterus and fallopian tubes. You must use a spermicide along with your diaphragm.

Diaphragms must be left inside your body for 6 hours after PIV sex. You should insert additional spermicide each time you have PIV sex.

You can leave a diaphragm inside for 24 hours. Leaving it in for a longer period of time may lead to a bacterial infection or toxic shock syndrome.

Diaphragms typically last around 2 years.

Like cervical caps, diaphragms are one of the least effective birth control methods available.

According to the Centers for Disease Control and Prevention (CDC), the typical use failure rate for diaphragms is 17 percent. The term “typical use” refers to the way diaphragms are used in real-world situations, as opposed to perfect use. Even if you intend to use your diaphragm perfectly, things can go wrong. For example:

  • Your diaphragm may become dislodged during PIV sex.
  • Your diaphragm may have microscopic tears that allow seminal fluid to get through.
  • You may forget to use spermicide for new PIV sexual activity.
  • You may remove your diaphragm too quickly after PIV sex.

Diaphragms have the same advantages that cervical caps do. These are:

  • affordability
  • don’t contain hormones
  • can be inserted prior to sexual activity

In addition to these:

  • Diaphragms typically last longer than cervical caps, provided they are cleaned and dried correctly.
  • Diaphragms may be better at preventing pregnancy in people who have already given birth vaginally.

Diaphragms are larger than cervical caps. Unlike cervical caps, which only cover the cervix, diaphragms cover some surrounding area. This part of the vagina is called the ectocervix.

Cervical caps, which are smaller, are designed to provide a snugger fit directly on top of the cervix. This difference in size may make diaphragms more effective for people who have already had a baby that was delivered vaginally.

According to some data, diaphragms provide 6 hours of protection after insertion. Cervical caps provide up to 48 hours of protection after insertion. However, both require the insertion of additional spermicide before each round of PIV sex.

Cervical caps can remain in place for up to 48 hours prior to removal. Diaphragms must be removed within 24 hours.

Both cervical caps and diaphragms are free for most people who have health insurance.

If you don’t have insurance, you may pay around $100 for a cervical cap and $90 to $120 for a diaphragm. This doesn’t include the cost of the doctor’s appointment you will need for fitting. It also doesn’t include the cost of spermicide.

Ask your doctor if they can give you a coupon that will reduce the cost of your cervical cap or diaphragm. You may also be able to download an app or coupon that reduces the cost of these devices and other prescription drugs.

Cervical caps and diaphragms both:

Some people think that using a spermicide provides protection against STIs. However, neither diaphragms nor cervical caps will protect you against STIs or STDs such as:

Cervical caps and diaphragms are vaginal barrier birth control methods. Both are less effective than contraceptives, such as IUDs and birth control pills.

Diaphragms and cervical caps are hormone-free. This makes them a viable birth control method for some people who may experience side effects to other methods. Just remember: Both cervical caps and diaphragms require a doctor’s prescription, and neither protects against STIs.