Infertility is defined as the inability to conceive after one year of regular sexual intercourse. About 60 to 70 percent of all couples who try to conceive will succeed within six months. Another 20 percent will conceive within a year. The remaining 10 to 20 percent have a medical condition that interferes with conception.

Infertility is an increasing problem in the United States. Approximately one quarter of all women can expect to have at least one episode of infertility during their childbearing years. Statistics show that in about 40 percent of cases, the cause of infertility lies in the female. In another 40 percent of cases, the cause lies with the male. Of the remaining number, either both partners have a fertility problem or no cause is ever found, although the number of undiagnosed cases is decreasing as better diagnostic methods are introduced.

In order for pregnancy to occur, a man must produce sperm in sufficient quantity and quality and a woman must produce a healthy egg, or ovum. The sperm must travel through the vagina and up through the uterus to meet the ovum while it is in one of the fallopian tubes. The timing of sexual intercourse is important. While sperm usually live for a few days, an ovum can be fertilized only during a 12- to 24-hour period. After the egg is fertilized, it must travel down to the uterus and successfully implant in the uterine lining.

Many theories have been proposed to explain an increasing number of infertile couples. More women are postponing pregnancy until they are in their thirties, a time when fertility begins to decline. Age also increases the possibility of multiple sexual partners, which increases the risk of sexually transmitted diseases that could lead to pelvic inflammatory disease and infertility. Age increases exposure to environmental and industrial toxins which may affect fertility. Unhealthy lifestyle choices, such as smoking, alcohol and drugs, also may affect fertility.

Infertility in a woman can be caused by a variety of medical conditions. Problems include failure to ovulate, hormonal imbalances that leave the uterine lining unprepared for implantation of the embryo, abnormalities of the uterus, scar tissue from infections in the fallopian tubes or on the ovaries or in the uterus, inadequate cervical mucus, production of antisperm antibodies, or habitual miscarriage. Endometriosis, uterine fibroids, or uterine polyps in a woman also can inhibit conception and implantation.

Infertility in a man can be traced to inadequate sperm production or function from a variety of causes: anatomical defects, chromosomal abnormalities, hormonal deficiencies, or sexual dysfunction.