Sperm donors up to the age of 45 are just as likely to conceive children as those in their 20s, a large study has shown.

The findings dispel the myth that a woman's chances of IVF success are lowered if she has to rely on sperm from an older man.

By encouraging more men to come forward as donors, they could help alleviate the sperm shortage faced by fertility clinics.

But researchers warned that older men in the general population should not assume they are also as fertile as their younger peers.

This is because all men who get through the stringent donor screening process, almost by definition, have high quality sperm.

Dr Navdeep Ghuman, from Newcastle Fertility Centre, who took part in the study of more than 230,000 sperm donation treatments, said: "What's reassuring is that there's no decline observed with increasing age of the men.

"The scary idea in the media and women's minds that older sperm means less chance of conceiving wasn't seen.

"We wanted to answer the question, does the age of a sperm donor matter? The short answer is no, it doesn't.

"The take-home message is that live birth rate does not decline with the age of male donors up to the age of 45.

"Hopefully this study will give women a message that their chances will not be compromised if they have to choose an older donor."

Using data stored by the fertility regulator, the Human Fertilisation and Embryology Authority, researchers analysed the success of sperm donations from men aged 20 and under to 45.

They found that live birth rate fell with the increasing age of women, dropping from 29% for those aged 18 to 34 to just 14% for the over-37 age group.

But within each of these groups, the age of the sperm donor had no impact. In fact, a slightly - non significant - greater proportion of sperm donors aged 41 to 45 fathered children than did those in their 20s.

Dr Meenakshi Choudhary, who led the Newcastle Fertility Centre team, said: "This trend of less likelihood of live birth with younger sperm donor might simply be explained by the fact that younger men who donate sperm are less likely to have proven fertility themselves than older sperm donors with proven fertility."

She added: "Our study shows that we are good at selecting the right sperm donors with the right sperm quality."

The findings are to be presented at the annual meeting of the European Society for Human Reproduction and Embryology taking place this week in Munich.

Even though age may not reduce an older sperm donor's chances of conceiving, a question mark still remains over the potential risk of genetic birth defects in his children.

There is some evidence that children of older fathers are more likely to suffer from brain disorders such as autism and schizophrenia, or growth abnormalities.

Professor Allan Pacey, senior lecturer in reproduction and developmental medicine at the University of Sheffield and chairman of the British Fertility Society, said: "I think I would be worried about raising the age limit for sperm donors to 45 because of the possible effects on the health of children."

He said that for every 100 men who apply to be sperm donors, only about five are accepted. A quarter of all donated sperm used in clinics was imported from outside the UK.

"We are selecting on the basis of sperm quality," said Prof Pacey. "I get little whispers, with pressure increasing due to the lack of sperm donors, that people are not adhering to accepted levels of sperm quality, and that is a worry. We simply don't have enough sperm donors in the UK."