Infertility is the failure of conception in a couple having regular, unprotected coitus for one year, provided that normal intercourse is occurring not less than twice weekly.

The time period is arbitrary. It relates to the natural rates of conception, ie 80% of couples will be pregnant after 12 cycles. Of those who have not conceived after 12 cycles, about 50% will conceive during a second year of attempted conception. After this second year of attempted conception, the chances of conception in those couples remaining is about 50% in the following four years.

Primary infertility applies to a couple without a prior pregnancy. Secondary infertility is used when the couple have previously succeeded in achieving at least one pregnancy, including abortion and ectopic pregnancy.