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Last Updated: Sunday, 29 May, 2005, 23:18 GMT 00:18 UK
Fast-freeze 'boosts egg survival'
Image of freezing in the lab
Current freezing techniques can damage many of the eggs
Scientists are hopeful they have found a better way to preserve the eggs of women undergoing cancer treatment, whose ovaries often end up damaged.

Current methods for freezing eggs before cancer treatments can damage the eggs as ice crystals form.

A University of Michigan team has had good results in mice with an instant freezing method called vitrification, during which crystals do not form.

They said nearly double the number of eggs were "surviving" the new process.


Taiwanese scientists have already reported a successful pregnancy in a woman whose eggs had been fertilised and put into her womb after vitrification.

But despite their success, the technique is still experimental and needs more work, which is why Dr Gary Smith and his colleagues from the Comprehensive Cancer Center at Michigan have been looking at mice.

They have also preserved eggs from one patient, but will not offer the technique routinely until it has undergone many more trials.

Using vitrification, we are getting 98% survival.
Researcher Dr Gary Smith

Unlike regular freezing, which creates ice crystals that can damage the egg as it thaws, vitrification cools eggs fast enough that the transformation from liquid to solid is instantaneous.

This means no ice crystals form.

Lead investigator Dr Smith said: "With traditional slow-freezing techniques, just over half the eggs survive the thawing process.

"Using vitrification, we are getting 98% survival.

"For a woman with cancer, these are the only eggs she is ever going to have, so it's important that as many as possible remain viable."

In the mice, 80% of the eggs or oocytes that were preserved with vitrification were able to become fertilised.


About 30% of these grew to become baby mice, which is comparable to the success rate with conventional IVF treatment on eggs that have never been frozen, said Dr Smith.

If this work bears out and the success rate is that high, it would revolutionise the way that we preserve eggs.
Dr Allan Pacey of the British Fertility Society

However, there are some hurdles to vitrification.

Eggs have to be matured before they are preserved. This means a woman must have 14 days of hormone treatment.

However, some cancers such as breast tumours grow more when they are exposed to hormones.

Also, the start of the cancer therapy might have to be delayed while the egg is being matured for vitrification.

These factors could limit its applications for some women, said Dr Smith.

Egg preservation procedures are also controversial because, in theory, it could enable women to put off getting pregnant until later in life, perhaps after concentrating on their careers.

Dr Allan Pacey, from the University of Sheffield and secretary of the British Fertility Centre, said: "If this work bears out and the success rate is that high, it would revolutionise the way that we preserve eggs.

"This is an area that warrants attention and is laudable. Women with cancer suffer greatly.

"Of course, some women may not want to delay their chemotherapy and if the cancer is oestrogen-sensitive then you might not want to stimulate the eggs with hormones.

"Obviously, we need more research in humans."

Dr Smith will present his work at the 13th World Congress on IVF Assisted Reproduction and Genetics in Turkey.

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01 May 05 |  West Midlands
Q&A: Frozen egg IVF
11 Oct 02 |  Health

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