The problem of subfertility occurs frequent and is constant.

Internationally, 15% of couples have difficulty in conceiving in general, or in conceiving the desired number of children, according to estimations of the World Health Organization (WHO).

The probability of conception by a couple of reproductive age who have regular unprotected sexual intercourse with no use of contraceptives is 20% per month. If we add the monthly conception probability (20%) for 12 months, the percentage of conception reaches statistically 93%, instead of a simple addition that would result in 240%.

The subfertility percentage remains stable through the centuries. It had been recorded that in a region of England in the 19th century, 1 out of 6 marriages was not productive (16%).