A soft, rubber cup that fits over a woman's cervix. A woman can put it in her vagina and keep it there during and after vaginal sex, with cream or jelly spermicide. Diaphragms are about the size and shape of a tennis ball cut in half. A doctor fits the right sized diaphragm for each woman's cervix. This stops a woman from getting pregnant. It does not stop the male or female from getting HIV from each other or germs that cause other STDs.