A cervical cap is a latex, thimble-shaped device that is inserted into the vagina and fits snugly over the cervix. Suction keeps the cap in place. A cervical cap provides a barrier to block sperm from entering the uterus and prevents fertilization. After intercourse, it should be left in place for 8 hours. A cervical cap is used with spermicidal jellies or creams that kill sperm. As birth control, cervical caps are 84-91% effective for women who have never given birth. They are 68-74% effective for women who have given birth. Cervical caps offer limited protection against sexually transmitted infections, but do not protect against HIV/AIDS.