What Causes Infertility?

In rough terms, about one-third of infertility cases can be attributed to male factors, and about one-third to factors that affect women. For the remaining couples, infertility is caused by a combination of problems in both partners or, in about 10 percent of cases, is unexplained.

The most common male infertility factors include azoospermia (no sperm cells are produced or none in the ejaculate) and oligospermia (few sperm cells are produced). Sometimes the vas deferens is blocked. For some men, the sperm cells are malformed or they die before they can reach the egg. In rare cases, infertility in men is caused by a genetic disease or a chromosomal abnormality.

The most common female infertility factor is an ovulation disorder. Other causes of female infertility include blocked fallopian tubes, which can occur when a woman has had pelvic inflammatory disease or endometriosis (a sometimes painful condition causing adhesions and cysts). Congenital anomalies (birth defects) involving the structure of the uterus or uterine fibroids are associated with infertility or repeated miscarriages.