Some women have tissue growing outside the uterus that's similar to the tissue that lines the uterus. It can grow on the ovaries, fallopian tubes, bladder, intestines, and other parts of the body. When it's time for your period, these clumps of tissue break down. But the tissue has no way to leave your body. While this is rarely dangerous, it can cause pain and form scar tissue that may make it tough to get pregnant. There are several treatment options. Pain medications, birth control pills, hormone medications to stop or reduce periods, surgery with small cuts, and even a hysterectomy (surgery to take out your uterus) are options.