Endometriosis is usually a long-lasting (chronic) disease. When you have endometriosis, the type of tissue that lines your uterus is also growing outside your uterus. The clumps of tissue (called implants) may have grown on your ovaries or fallopian tubes, the outer wall of the uterus, the intestines, or other organs in the belly. In rare cases they spread to areas beyond the belly.
With each menstrual cycle, the implants go through the same growing, breaking down, and bleeding that the uterine lining (endometrium) goes through. This is why endometriosis pain may start as mild discomfort a few days before the menstrual period and then usually is gone by the time the period ends. But if an implant grows in a sensitive area, it can cause constant pain or pain during certain activities, such as sex, exercise, or bowel movements.
Some women have no symptoms or problems. Others have mild to severe symptoms or infertility. There is no way to predict whether endometriosis will get worse, will improve, or will stay the same until menopause.
Between 20% and 40% of women who are infertile have endometriosis (some have more than one possible cause of infertility).1 Experts don't fully understand how endometriosis causes infertility. It could be that:2
- Scar tissue (adhesions) may form at the sites of implants and change the shape or function of the ovaries, fallopian tubes, or uterus.
- The endometrial implants may change the chemical and hormonal makeup in the fluid that surrounds the organs in the abdominal cavity (peritoneal fluid). This may change the menstrual cycle or prevent a pregnancy.
A common complication of endometriosis is the development of a cyst on an ovary. This blood-filled growth is called an ovarian endometrioma or an endometrial cyst. Endometriomas can be as small as 1 mm or more than 8 cm across. The symptoms of an ovarian cyst may be the same as those of endometriosis.