Infertility is much more common than most people imagine. Large population studies show that as many as one in six couples are affected at some time in their reproductive lives. Doctors usually define infertility as the inability to conceive after one year of trying.
Primary and secondary infertility
There are two sources of infertility, one ‘primary’, the other ‘secondary’. The first describes a physiological condition in couples who have never been able to conceive, despite continued trying; the second describes an acquired state of infertility in a couple who have had a pregnancy in the past.
Most but not all causes can be explained by investigation. While one-third of all infertility cases can be explained by female causes and one-third by male, there remains a further third for which no clear explanation can be found. All the tests - for both male and female - show normal results. This is especially so in cases of ‘secondary’ infertility, in which the couple already has one or more children naturally conceived.