In some women, there is tissue growing outside the uterus that is similar to tissue that lines the uterus. It can happen 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 the 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, hormones to stop periods, surgery with small incisions, and even a hysterectomy (taking out your uterus) are options.