An over-the-counter form of birth control that uses a slightly cup-shaped soft sponge, saturated with a spermicide, to form both a physical and chemical barrier to sperm. Before intercourse, the sponge is inserted into the vagina and positioned to cover the cervix. It should be left in place for at least six hours after intercourse and up to 24 hours, during which time intercourse can be repeated if desired. Sometimes women or their sexual partners have allergic reactions to the sponges. The sponge can sometimes fragment on removal, causing infection, and on rare occasions it has been linked with cases of toxic shock syndrome. The effectiveness rate of the cervical sponge as a contraceptive is about 80 to 87 percent, the Food and Drug Administration estimates.