Lowell Massachusetts - This dome-shaped, silicone cup is used in conjunction with spermicide. The diaphragm is filled with spermicide then inserted into the vagina and covers the cervix thus preventing sperm from entering the uterus. The diaphragm needs to be inserted properly for every sexual encounter and removed thereafter for effectiveness. If always used as directed, 6 out of 100 will become pregnant each year. If not used as directed, 12 out of 100 will become pregnant each year.