Endometriosis occurs when tissue that normally grows in the uterus implants and grows in other locations. This extra tissue growth — and the surgical removal of it — can cause scarring, which may obstruct the tube and keep the egg and sperm from uniting. It can also affect the lining of the uterus, disrupting implantation of the fertilized egg. The condition also seems to affect fertility in less-direct ways, such as damage to the sperm or egg.

Uterine or cervical causes

Several uterine or cervical causes can impact fertility by interfering with implantation or increasing the likelihood of a miscarriage.

• Benign polyps or tumors (fibroids or myomas) are common in the uterus, and some types can impair fertility by blocking the fallopian tubes or by disrupting implantation. However, many women who have fibroids or polyps can become pregnant.
• Endometriosis scarring or inflammation within the uterus can disrupt implantation.
• Uterine abnormalities present from birth, such as an abnormally shaped uterus, can cause problems becoming or remaining pregnant.
• Cervical stenosis, a cervical narrowing, can be caused by an inherited malformation or damage to the cervix.
• Sometimes the cervix can’t produce the best type of mucus to allow the sperm to travel through the cervix into the uterus.