Around 1 in 7 heterosexual couples in the UK seek advice at some time in their lives about difficulties in getting pregnant. The time it takes to conceive naturally varies and age can be an important factor: both women's and (to a lesser extent) men's fertility gradually declines as they get older.
A woman may have fertility problems because her ovaries do not produce eggs regularly, or because her fallopian tubes are damaged or blocked and the sperm cannot reach her eggs. In men, a fertility problem is usually because of low numbers or poor quality of sperm. For up to a quarter of people, no reason can be found for their fertility problems. This is known as unexplained infertility.