IT'S not just women who have a ticking biological clock.
A fertility study has found the chances of men fathering children also falls with every passing year once they reach middle age.
Analysis of patients at an infertility clinic found that the chances of a man getting his wife pregnant dropped by 7pc cent each year between the ages of 41 and 45.
Until now the pressure has been on women to start a family before they turn 40, when the chances of them getting pregnant starts to decline sharply as the number and quality of their eggs begins to decline.
But experts say that men should not leave it too late either if they want to be sure of having children.
Lead researcher Dr Paula Fettback, of the Huntingdon Reproductive Medicine Centre in Brazil, said: "Of course it's not the same as for women, but men can't wait for ever. After 45 if they haven't, they have to start thinking about having children."
In the study, presented this week at the American Society for Reproductive Medicine in Florida, she analysed the outcome of 570 IVF treatments carried out this year.
To make sure that the age of the woman did not skew the study, only cases where eggs were donated by young healthy women were included.
The results showed that the age of men in the group that did not conceive was "significantly higher" than among those who were able to have a baby.
Dr Fettback said: "The contribution of female age on reproduction is well known however the contribution of male age is not well understood.
"As a growing number of men are choosing to father children at older ages, comprehending the impact of male age on fertility has become incredibly important in public health."
Charles Kingsland, a consultant gynaecologist at Liverpool Women's Hospital said the study should be treated with caution as it was very small and carried out retrospectively.
"There are lots of advantages to being a younger father, you have more energy, but being an older father does confer certain advantages such as stability, wisdom and maybe a bit more financial security."