It may be that one partner cannot contribute to conception, or that a woman is unable to carry a pregnancy to full term. It is often defined as not conceiving after 12 months of regular sexual intercourse without the use of birth control.

In the United States, around 10 percent of women aged 15 to 44 years are estimated to have difficulty conceiving or staying pregnant. Worldwide, 8 to 12 percent of couples experience fertility problems. Between 45 and 50 percent of cases are thought to stem from factors that affect the man.