The scale of the problem A normal fertile couple in their mid-20s having regular sex have a one in four chance of conceiving each month. This means that around nine out of ten couples trying for a baby will conceive within a year. However, one in ten will not - and within this 10 per cent are those couples who will be diagnosed as infertile.
Doctors usually define infertility as the inability to conceive after at least one year of trying.
Estimates indicate that around one third of all infertility cases are the result of a male problem - most commonly related to the quality and quantity of sperm of the male partner. Because the sperm characteristics required for 'normal' fertilization are well known, any abnormal results from a sperm test will suggest a male problem. These tests, which are carried out on a semen sample, can reveal abnormalities in sperm numbers, movement and shape. In recent years, specialist infertility clinics have also used in vitro fertilization as a diagnostic test. Very often, healthy eggs fail to fertilize in the laboratory because of abnormal sperm function.