A correctly fitting diaphragm will cover the cervix and rest snugly against the pubic bone. A diaphragm that is too small might fit inside the vagina without covering the cervix, or might become dislodged from the cervix during intercourse or bowel movements. It is also more likely that a woman's partner will feel the anterior rim of a diaphragm that is too small during intercourse. A diaphragm that is too large will place pressure on the urethra, preventing the bladder from emptying completely and increasing the risk of urinary tract infection. A diaphragm that is too large may also cause a sore to develop on the vaginal wall.