Page last updated at 10:11 GMT, Monday, 10 November 2008

IVF screen 'boosts baby chances'

Baby lying on back
The technique may lead to more live births

Scientists have shown a technique to screen IVF embryos can double the chances of pregnancy for some women.

Comparative genomic hybridisation (CGH) enables doctors to scrutinise an embryo's chromosomes for abnormalities more closely than ever before.

The American Society of Reproductive Medicine heard that implantation rates using CGH were 62% - around twice that achieved by other screening methods.

Experts hope to start using the technique in the UK soon.

There is a dramatic change in implantation rate with this technology
Dr Dagan Wells
Oxford University

It is thought that many miscarriages are due to an embryo carrying an abnormal number of chromosomes.

As women age, the chances of this problem occurring become higher.

However, until now it has proved difficult to examine all the chromosomes in an embryo, meaning that screening techniques have only produced limited success in weeding out those with little chance of leading to a successful pregnancy.

CGH solves the problem by allowing doctors to look at every chromosome in the developing embryo.

In the latest study, experts from Oxford University analysed the results of a clinical trial carried out by researchers at the Colorado Centre for Reproductive Medicine in the US.

A total of 23 women, with an average age of 37 took part. Each had unsuccessfully tried IVF before.

The women's eggs were fertilised, and the resulting embryos were allowed to grow for five days until they reached the blastocyst stage when they were analysed using CGH.

As a result all 23 women had at least one normal embryo to transfer to their womb, and in total 50 apparently healthy embryos were transferred in 23 cycles of treatment.

This lead to 21 pregnancies, of which 18 passed the crucial first three months when most miscarriages occur.

Experts predict the live birth rate will be 78%. This compares with an anticipated 60% for the same patients without embryo screening.

Phenomenal results

Dr Dagan Wells, from Oxford University, described the results as "phenomenal".

He said: "Chromosomal abnormalities are the main cause of implantation failure and miscarriage, and a way of detecting them should improve success rates.

"There is a dramatic change in implantation rate with this technology.

"The pregnancy rates we've got so far are absolutely phenomenal."

Dr Wells has applied for a licence to start offering CGH to UK patients, at a cost of about 2,000 per screening.

CGH works by labelling chromosomes taken from cells in the blastocyst with a green fluorescent tag.

By the time an embryo has reached the blastocyst stage it is more robust, meaning that cells can be extracted for testing more safely.

This DNA is then mixed with the DNA of a chromosomally normal individual, which is tagged red.

The red chromosomes act as a kind of template to which the embryo's DNA attaches.

You can then determine whether there are too many or too few of any chromosome from the colour.

For example, if the embryo's cells carry an extra copy of chromosome 21 that chromosome will look green in the combined sample, but if the embryo has only one copy it will look redder.

Dr Allan Pacey, a fertility expert at the University of Sheffield, and member of the British Fertility Society, said older forms of genetic screening had proved to be of limited use at best.

He said: "There is a need to investigate whether new techniques are more effective."

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