Pregnancy occurs when an egg is released from the ovary into the fallopian tube, where it is fertilized by a sperm.

There are numerous reasons why this may not occur. One of them is severe endometriosis, a condition in which the lining of the uterus leaks into the abdominal region during menstruation. (Low to mild levels of endometriosis typically do not cause infertility.) Other common causes of infertility are a low sperm count or a damaged fallopian tube.

Infertility may also be the result of a previously performed medical "sterilization" procedure such as a vasectomy or tubal ligation.

In some cases, previous vasectomy reversals or tubal ligation reversals may not have been successful, thereby requiring a second operation by a qualified and highly skilled surgeon.