Occlusive diaphragms are barrier contraceptives placed in the vagina to block sperm from entering the cervix. They are most effective when used with a spermicide. Diaphragms must be left in place for at least 8 hours after sex and properly fitted to be effective. Refitting is required after childbirth or weight changes. The Dutch cap is a dome-shaped diaphragm made in varying sizes that fits over the cervix. Cervical caps also fit over the cervix but are preferred for women with prolapsed organs. While diaphragms are inexpensive and reusable, they do not prevent sexually transmitted infections like HIV.