Causes

Infertility can be attributed to factors in either the female partner or male partner. About one third of infertility cases can be attributed to male factors, and about one third to women. For another third, infertility is caused by problems in both partners. In some cases, the causes are never discovered.

Women

Here are some common causes of infertility in women:

• Age. Fertility rates slowly decline after age 35 because of decreasing ability to ovulate (produce eggs). Women are born with all of the eggs they'll ever have. As women age, so do their eggs. Eggs of women in their late 30s and in their 40s are more likely to have chromosomal abnormalities, which helps to account for the high rate of miscarriage and Down syndrome at this age.
• Adhesions (scar tissue formation) interfere with the ovaries and fallopian tubes. In endometriosis, endometrial tissue, which normally lines the uterus, implants over the ovaries and prevents the egg from entering the fallopian tube after ovulation. Pelvic inflammatory disease (PID), miscarriage and prior surgery also form adhesions, which may block the fallopian tubes and prevent the passage of an egg down to the uterus. PID is usually caused by a sexually transmitted disease. It can also stem from miscarriage, abortion, childbirth or an intrauterine device.
• Ovulatory dysfunction causes most cases of infertility. Ovulation makes eggs available for fertilization by sperm. Hormonal imbalance, such as in polycystic ovary syndrome, prevents maturation of eggs. Ovulation is absent or very irregular. Ovulatory dysfunction can be caused by hormonal abnormalities, too much exercise and other factors.
• Uterine fibroids may prevent implantation of the embryo or interfere with early fetal growth. Many women have fibroids, which are benign (non-cancerous) tumors. However, in some women fibroids can lead to first trimester miscarriage.

Men

The most common problems in men are azoospermia (no sperm cells produced) and oligospermia (few sperm cells produced)

Causes can include:

• Varicocele is a major cause of male infertility and occurs when a vein that carries blood out of the scrotum expands. A pool of blood forms around the testicles, raising the temperature of the scrotum. This high temperature affects sperm, which develop best in temperatures cooler than the body.
• DES exposure affects some men whose mothers took DES to prevent miscarriage in the 1950s and 1960s. These men may have a blockage of the vas deferens, one of the tiny tubes where sperm travels. DES sons are prone to fertility problems, such as undescended testicles and cysts in their reproductive tract.
• Ductal blockages, a result of an infection or birth defect, may occur in the small ducts that carry sperm from the testicles to the penis.
• Marijuana can lower sperm counts.
• Mumps.

More on Infertility

In the Encyclopedia:

This article was reviewed and updated June 2007.