The sites of infection that usually cause infertility are the fallopian tubes, the inflammation of which produces a condition known as salpingitis . Most infections are caused by sexually transmitted diseases. Chlamydia trachomatis is an infectious organism that causes a large proportion of salpingitis cases. Gonorrhea is responsible for much of the rest. Attacks of PID can eventually cause scarring, abscess formation, and tubal damage that result in infertility.
Endometriosis is responsible for a substantial proportion of cases.
It results when fragments of the endometrial lining are implanted in other areas of the pelvis, which then develop into cysts and respond to hormonal changes, increasing in size with each menstrual cycle and eventually causing scarring and inflammation. Endometrial implants in the ovaries or fallopian tubes are especially prone to cause infertility. These problems result in the failure of the ovarian follicle to rupture, an empty follicle, or entrapment of the egg so that it is not released. Some cases of unexplained infertility may result from early loss of ovarian function. Immune system failure can also cause infertility.