Diaphragms and caps are forms of contraception that prevent sperm from meeting and fertilizing an egg. They fit inside the vagina and cover the cervix (entrance to the womb). They can be made of rubber (latex) or plastic (polyurethane) and come in different shapes and sizes.
Vaginal diaphragms are circular domes with flexible rims. Caps are smaller than diaphragms. To be effective they need to be used with spermicide, which is a special cream that kills sperm.
Their effectiveness depends on how well they're used. When used according to the instructions, the effectiveness is usually greater than 90%.
Every time you have sexual intercourse, spermicide needs to be applied to the diaphragms or cap, and then inserted into the vagina to cover the cervix. They need to be left in the vagina for at least 6 hours after sex, but can be left in longer if necessary.
They can be inserted any time before sex, however if it's more than 3 hours before sex, you must apply more spermicide.
Advantages:
You only have to use it when you have sex
It has no serious health risks
There's a choice of different types
It can be put in at any convenient time before sex
It may give some protection against cervical cancer
Disadvantages
Putting it in at the time of sex can be an interruption
Some people find the spermicide messy
Some diaphragm users find they get cystitis (changing to a smaller diaphragm or cap can help)
Some people are sensitive to the chemicals in latex diaphragms or caps or to the spermicide
Oil-based lubricants such as body oils or lotions should not be used with latex diaphragms or caps
Diaphragms and caps don't suit everyone. They may not be suitable if you:
Have vaginal muscles that cannot hold a diaphragm
Have an unusual shape cervix, which means it may be in an awkward position to reach it