fertility, ability of an individual or couple to reproduce through normal sexual activity. About 90 percent of healthy, fertile women are able to conceive within one year if they have intercourse regularly without contraception. Normal fertility requires the production of enough healthy sperm by the male and viable eggs by the female, successful passage of the sperm through open ducts from the male testes to the female fallopian tubes, penetration of a healthy egg, and implantation of the fertilized egg in the lining of the uterus (see reproductive system). A problem with any of these steps can cause infertility.