New drugs are being developed that could stave off the menopause, it has been revealed.

They could lead to a fertility revolution, allowing women to wait longer to have a child.

The dramatic news came from fertility expert Professor Robert Winston. He told a conference that researchers had found a protein which they believe could be developed into a pill or an injection to extend the life of women's eggs.

This would give new hope for the thousands of women who find themselves left childless in later life.

Last week it was revealed that the number of women in their 40s having IVF treatment has soared more than tenfold over the past 15 years. But the chances of success fall dramatically after the age of 37 and are negligible by 45 - because by then very few eggs are being produced.

Professor Winston, professor of fertility studies at Imperial College, said: "We think we have identified a protein which might be used to prolong the life of those eggs. Women are much more healthy than they were and the period before the menopause could be extended without risk."

David Hodgson, medical director of the London Fertility Centre, said such a drug would have a dramatic impact. But he warned there would have to be thorough trials to make sure the treatment was safe.

Professor Winston, who has made frequent TV appearances, told a meeting at the Cheltenham Science Festival that research was still in the early stages.

He said more and more women were finding problems with infertility if they delayed having babies until later in life.

Professor Winston said: "What we are seeing is, increasingly, a society where women are waiting later and later to have their first baby. That's wholly admirable in every way.

"It shows how women are gaining full status as women in our society. They are getting educated and having careers."

But he stressed: "Their biology is working against them."

At the age of 16, said Professor Winston, a woman had 400,000 eggs - but by the age of 46 there will be virtually none left. He said women lost around two eggs an hour.

"In the time you've been listening to me speaking, every woman of child-bearing age in the audience will have lost two eggs," he said. "By contrast, I will have made 150,000 new sperm.

"We either arrange for women to train, and rear and care for children at the same time, or science can help by extending the length of life of eggs in the ovaries.

"We might be able to do that in the next decade or so. We might be able to use proteins to protect the eggs."

He did not give details on which proteins could be used or how far the research had progressed.

But Mr Hodgson warned that there would need to be stringent trials and there were several pitfalls which needed to be addressed.

He said: "Will this protein actually make these eggs safer?

"As women get older there is an increased risk of chromosomal abnormalities in their eggs, meaning their children are more likely to have problems. Will the protein stop this happening?

"Will the proteins have any side effects in any other systems of the body?

"Some studies have indicated that if HRT is taken after the menopause there are effects on breast cancer risks and blood coagulation - will the protein have the same effect?

"If this is safe, however, it would have a large impact on the IVF services we can provide."

A long programme of trials would mean the new drug, which could be delivered as a pill, a patch or a yearly injection - may not be available for many years. The drug could possibly be taken at the same time as HRT, to combat the actual nature of the menopause as well as just its side effects.

Last week the Human Fertility and Embryology Authority revealed that, over the past 15 years, the number of cycles of IVF given to women between 40 and 45 has increased more than tenfold.

The increase has come despite concerns over the health risk to mother and child of waiting until the 40s. Experts say too few women are aware that chances of success decline dramatically after the age of 40, and the rates of miscarriage increase.

Angela McNab, chief executive of the HFEA, said: "It is a matter of concern and it may well be that one of the messages we need to concentrate on is reminding people of the biological clock and the difficulties of achieving pregnancy after you are 40."

Tests are already available to tell a woman how fertile she is.

The "biological clock" blood test measures hormone levels which indicate how many healthy eggs a woman has left - and therefore how many years she has to start a family.

Guidelines from the National Institute for Health and Clinical Excellence say women over 40 should not be given IVF in most cases because of the poor chance of success.

This means the majority of women in their 40s pay privately - around ยฃ4,000 to ยฃ8,000 per cycle.

Success rates for all ages have risen between 1991 and 2004, up from 14 per cent to 21 per cent. But for women aged 40, the rise has been far less dramatic - last year only around 12 per cent had a successful pregnancy with IVF.

For women of 44 the success rate is less than 3 per cent - almost the same as a decade ago.

Speaking last week the HFEA's information director Dr David Tells said: "The message we need to get across is that it is kind of impossible to beat nature. The influence that clinicians have to affect success rates declines as age increases."