By DANIEL MARTIN

Last updated at 23:27 20 April 2008

Women who decided to have a caesarean have a slightly lower mortality rate according to a new study

A major breakthrough by British scientists could bring new hope for women facing the heartbreak of infertility.

For the first time a team has managed to grow hundreds of eggs in the laboratory using a new technique which could help cancer patients whose treatment can leave them infertile.

It would also allow thousands more women to wait until middle age to have children.

The scientists from Edinburgh University have shown that immature eggs can be frozen, grown and matured in the lab.

The process could lead to women having pieces of ovary containing the immature eggs removed and stored. Much later on, they could be thawed, fertilised and finally implanted into the womb.

The breakthrough, which comes as MPs prepare to debate the controversial Human Fertilisation and Embryology Bill, raises again the ethical debate surrounding the freezing of eggs.

Some say it is morally wrong for a woman to do so and have them fertilised years later in order to delay having children while she pursues a career.

However, scientists hope the new process will revolutionise fertility preservation for women because it will allow them to store many more eggs than they can under traditional IVF techniques.

And, because immature eggs survive the freezing process much better than the mature ones used in IVF, it is much more likely that older women will be able to conceive using them.

It brings forward the prospect that thousands of women will use the technique to side-step the menopause, delaying motherhood for the sake of their careers.

The process, which could be available in five years, also provides hope for cancer sufferers who at the moment are often left infertile following chemotherapy and radiotherapy.

Powerful anti-cancer drugs can destroy follicles in the ovaries, wiping out any possibility of women having children.

At the moment, these women have a piece of ovary removed, frozen and then re-transplanted after their cancer treatment. But there is always the danger that the cancer could be reintroduced by the implant.

The new technique means women's immature eggs contained in the patch of ovary could be grown in the lab and then screened for cancer before being used in IVF treatment.

There are also hopes it will provide a rich source of eggs for scientists to study for clues on ways to treat a range of diseases.

There is a shortage of human eggs for medical research, and if the technique works it would bypass the controversy over the use of animal-human 'hybrid' embryos.

The Human Fertilisation and Embryology Bill, which MPs are due to debate next month, would allow scientists to use these embryos in medical research, but many MPs plan to vote against.

The research, carried out by an Edinburgh University team led by Dr Evelyn Telfer, is published today in the journal Human Reproduction.

"This is a significant step in developing immature eggs to maturity outside the body," said Dr Telfer.

"Women who face infertility as a result of chemotherapy, or who want to put their biological clock on hold, could benefit from this system.

"However, there is a lot more research to be carried out before this technique could be safely applied within a clinical setting."

Last year, Canadian scientists announced the first birth of a child created from a human egg matured in the laboratory.

However, they did not use the same "primordial follicles" studied by the researchers from Edinburgh.

These are the tiny egg-bearing pockets within the ovaries that are present in their millions at birth, but gradually die off over the course of a woman's life.

They represent a woman's fertility "battery" which once depleted cannot be recharged.

Many remain dormant, but some go on to mature and eventually release their eggs in preparation for fertilisation.

For the first time, the team led by Dr Telfer has succeeded in growing primordial follicles to a late stage of maturation in the lab.

They took pieces of ovary containing the follicles from six volunteer women who were giving birth by caesarean section.

These were then exposed to a chemical that promotes growth, similar to the one that functions in the ovaries.

Around a third of them survived and went on to reach the advanced 'antral' stage of development.

At this stage, the follicles are filled with fluid and contain eggs almost ready to be fertilised.

It means that it could soon be possible to grow hundreds of eggs in the laboratory.

The Canadian team which managed to create a child from immature eggs was working with only around a dozen.

Another advantage is that the follicles mature much more quickly in the lab than they do in the ovary.

The scientists do not yet know whether eggs - or oocytes, to give them their technical name - matured in this way are completely normal and suitable for in-vitro fertilisation. But animal studies suggest they are.

The next step is to use hormones and other substances to try to nudge the 'antral' eggs on to the next stage of maturation, and then test the technique on humans.

"We believe there's good evidence that we can get normal oocytes, but of course you would never apply this technique clinically until you are sure," said Dr Telfer.

"We're seeking funding for further research to bridge that gap. It might take five to ten years from now before we get to the stage of a clinical trial."

Dr Jane Stewart, consultant in reproductive medicine at the Newcastle Fertility Centre, said:

"This work increases our understanding of the maturation of human eggs in the lab and takes us a step nearer the goal of strong immature eggs for fertility preservation for women."