Diaphragms, cervical caps and shields are placed inside the vagina, directly over the cervix. These devices physically block sperm from entering the uterus.

The diaphragm is usually saucer shaped and made of latex rubber, although it is also available in a hypoallergenic material. The cervical cap looks like a large thimble and, similar to a diaphragm, is made of latex but is also available in non-allergenic silicone rubber. Lea’s shield is a silicone cap that fits over the cervix. It has a loop to make removal easier, and a one-way valve so that it can be used during menstruation. Diaphragms, cervical caps, and shields are always used with a spermicidal jelly or cream to kill any sperm that manage to bypass the device.

The diaphragm, cervical cap or shield may be inserted with spermicidal cream or jelly up to six hours before sexual intercourse, allowing for greater spontaneity.

After intercourse, the diaphragm must be kept in position for at least six hours to ensure that all the sperm inside the vagina are dead. If you have sex again, the spermicidal jelly or cream will need to be reapplied beforehand. The cap and shield should be left in place for at least eight hours.

The diaphragm provides effective contraception for up to 6 hours, and should not be left in the vagina for longer than 24 hours after you have sex. The cervical cap and shield, however, can remain safely in position for up to two days.

With typical use, the diaphragm is about 82 to 86 percent effective in preventing pregnancy. It is up to 97 percent effective with perfect use. The cervical cap is about 80 to 84 percent effective with typical use, and about 91 percent effective with perfect use among women who have not had children. However, the cervical cap is less effective in women who have already given birth. Lea’s shield is about 85 percent effective in preventing pregnancy with typical use.

Advantages

• Use of a diaphragm, cervical cap or shield does not interrupt or alter fertility. Pregnancy is possible whenever the device is not used during sexual intercourse.
• In addition to birth control, these devices somewhat reduce the risk of sexually transmitted infection, but not as effectively as condoms.

Disadvantages

• The diaphragm and cervical cap need to be properly fitted by a medical provider to guarantee the correct size. The medical provider will write a prescription for the correct size, determined by pelvic examination. The prescription can be filled at most drugstores or pharmacies.
• To be effective, the device must be correctly positioned. Improper use and forgetting to use the device are the most common reasons for this method's failure, resulting in unplanned pregnancy. If the device is removed too soon, it's possible for some remaining live sperm to travel up inside the uterus and fertilize an egg, resulting in pregnancy.
• Forgetting to remove the diaphragm after 24 hours may lead to smelly vaginal discharge and inflammation, and/or infection. The severity of this problem depends on the number of days the diaphragm is left in the vagina.
• Urinary-tract infections are two to three times more common in women using diaphragms than in those using other methods, such as the birth-control pill. This may be caused by the rim of the device pressing up or rubbing against the back wall of the urethra during the motion of intercourse, which may irritate the bladder and make bacterial infection more likely. If this problem recurs, antibiotics may be taken around the time of intercourse to decrease the chance of bladder infection.