Successful pregnancy requires ovulation (when an ovary releases an egg into a fallopian tube), transport of the egg partway down the fallopian tube, movement of sperm from the vagina to the fallopian tube, penetration by the sperm of the egg's protective layer, and implantation of the fertilized egg in the uterus.

In the United States, infertility is an issue of great concern to many couples of childbearing age. More than 15 percent of all such couples are estimated to be infertile. In a 1995 study by the Centers for Disease Control and Prevention, 10 percent of 10,847 women interviewed, a percentage that represents 6.1 million women of childbearing age nationwide, reported having experienced some problems getting pregnant or carrying a baby to term. Of this group, about half were fertile themselves but had infertile partners. The number of women seeking professional assistance to deal with infertility problems is increasing every year...