Infertility is defined as the inability for a couple to become pregnant after a year of regular, unprotected intercourse. The male partner, the female partner, or both, may have a fertility problem. In women over 35 years old, an evaluation and possible treatment is needed after 6 months of unprotected intercourse.

A person who is infertile has a reduced ability to have a child. It usually doesn't mean a person is sterile — that is, physically unable ever to have a child. Up to 15% of all couples are infertile, but only 1% to 2% are sterile. Half of couples who seek help can eventually bear a child, either on their own or with medical assistance.

Men and women are equally likely to have a fertility problem. In about one in five infertile couples, both partners contribute to fertility problems, and in about 15% of couples, no cause is found after all tests have been done. This is called "unexplained infertility."

For many couples, infertility is a crisis. Fertility problems often come with feelings of guilt or inadequacy. But a diagnosis of infertility is not necessarily a verdict of sterility.