A: No one can be blamed for infertility any more than anyone is to blame for diabetes or leukemia. 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 one-third of infertile couples, infertility is caused by a combination of problems in both partners or, in about 20 percent of cases, is unexplained.
The most common male infertility factors include azoospermia (no sperm cells are produced) and oligospermia (few sperm cells are produced). Sometimes, 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 such as cystic fibrosis 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 and uterine fibroids are associated with repeated miscarriages.