Thirty to 40 percent of women with endometriosis also suffer from infertility. The exact link between endometriosis and infertility is not fully understood, but several symptoms of endometriosis can contribute to infertility. Endometriosis occurs when the cells that line the uterus (the endometrium) grow outside of the uterus. This misplaced endometrial tissue grows and dies in response to monthly hormones, causing local bleeding and the release of chemicals that irritate the surrounding tissue, causing pain, scarring and adhesions.
Endometriosis and Egg Quality
When endometriosis is found on the ovary, it can form invasive cysts called endometriomas. Endometriomas grow and die in response to monthly hormones, filling with blood and secreting various chemicals that negatively impact the quality of eggs in the surrounding ovarian tissue. Eggs near endometriomas are less likely to be fertilized than eggs from an ovary without endometriomas. Women undergoing in vitro fertilization treatments who have endometriomas are more likely to have their stimulation treatment canceled due to poor hormonal response and have fewer eggs recovered than women without endometriomas, as reported by Dr. Yan-hong Mao, Dr. Chun Zhou and Dr. Annie Zaccabri in the July 2009 issue of the Journal of Reproduction and Contraception.
Scarring of Reproductive Organs
Another symptom of endometriosis that may contribute to infertility is scarring and the formation of adhesions on and around various reproductive organs. When endometriosis grows on the Fallopian tubes or ovaries, it creates wound-like areas of bleeding and inflammation that scar, causing adjacent tissue to grow together, forming adhesions. Adhesions can create mechanical barriers to fertility. For example, the Fallopian tube can become stuck to the ovaries, blocking the release of eggs at the time of ovulation. Scarring in the Fallopian tube can block the opening to the tube, which prevents egg and sperm from coming together, blocking fertilization. Likewise, ovaries can adhere to other organs within the pelvic cavity, blocking normal ovarian function and causing pain.
Endometriosis and Embryo Implantation
Endometriosis may interfere with embryo implantation at the molecular level. Embryo implantation occurs as a result of complex molecular signaling pathways between the implanting embryo and the cells of the uterus. Women with endometriosis can have problems with embryo implantation, causing infertility. Scientists at the University of Chicago used a primate research model (baboon) with endometriosis to look at the molecular events that occur during embryo implantation. In their study published in the June 2004 Journal of Reproductive Biology and Endocrinology, Dr. J.J. Kim and Dr. Asgerally T. Fazleabas found that several genes critical for proper implantation were down regulated or abnormally expressed, disrupting the molecular pathway required for normal implantation.
