The lining tissue of the uterus is called the endometrium.  Each month (except during pregnancy) this lining is shed through the cervix and into the vagina during the menstrual period.  However, some of the blood and lining cells may exit the uterus in the wrong direction, flowing up through the fallopian tubes and into the abdominal cavity.  This is sometimes called retrograde bleeding.  It is a fairly common occurrence, but usually the body’s immune system recognizes that these cells are in the wrong place and eliminates them.

For unknown reasons, in some women these uterine lining cells may grow outside the uterus.  They may grow in or on the ovaries, in the fallopian tubes, on the outer surface of the uterus, or on other areas of the membrane that lines the abdominal cavity.  The cells still behave like uterine lining cells, however – growing full of blood and nutrients in preparation to receive an egg and bleeding afterwards as in normal menstruation.  This condition is called endometriosis.  The blood and other biochemicals released by the endometriosis cells begin to irritate the surrounding tissues, causing pelvic pain.  Eventually the body may form scar tissue around these injuries, which can lead to more pain.

Endometriosis is a common gynecological condition among American women of all ages, races and backgrounds.  It is more common in women in their 20’s and 30’s, but even adolescents can develop endometriosis.  Because endometriosis responds to the monthly release of female hormones (estrogen and progesterone), it decreases and eventually disappears with menopause.

Although the exact cause or causes are not understood, there seems to be a genetic component.  A woman whose mother or sister has had surgically proven endometriosis has a sevenfold higher risk of developing the condition than women in the general population.

In addition to causing pelvic pain, endometriosis can affect fertility.  Mild cases can reduce the chance of getting pregnant from the normal 25% per month to around 7% per month, for a healthy woman in her 20s.  More extensive endometriosis that involves scarring, blocking of the fallopian tubes or large cysts in the ovaries (endometriomas) reduce these chances further.

When a woman complains of chronic pelvic pain, pain with sex, low back pain, painful bowel movements or sudden, knifelike pelvic pain, her physician may suspect endometriosis.  Sometimes it can be felt during the rectal part of a pelvic examination as tender, thickened areas near the uterus.  A sonogram can reveal the presence of an ovarian cyst and may show patterns characteristic of endometriosis.  However, the only way to obtain a definite diagnosis is with visual inspection of the organs, which is done by laparoscopy.

Both medical and surgical approaches are available to treat endometriosis, and both have had good success rates at reducing pain and improving fertility.  If surgery is required, endometriosis can usually be treated with laparoscopic surgery.


  1. American College of Obstetricians and Gynecologists. Gynecological Problems: Endometriosis. 2001. www.acog.org/publications/patient_education.pdf/bp013.cfm.
  2. American Society for Reproductive Medicine. Pelvic Pain: A Guide for Patients. Patient Information Series 1997. www.asrm.org/patients/patientbooklets/pelvicpain.pdf.
  3. Parker WH. A Gynecologist’s Second Opinion. (c)2003; A Plume Book; Published by the Penguin Group, New York, NY.
  4. Society of Laparoendoscopic Surgeons. Endometriosis. Patients>Information on Laparoscopic and Endoscopic Procedures. 2004 http://www.sls.org/ | http://www.laparoscopy.org/
Copyright 2023 AAGL. By using this site, you agree to our Terms of Service and Privacy Policy
Last updated on Jun 9, 2023