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First major study of comprehensive genetic screening technique

25 October 2010
Appeared in BioNews 581
The first formal clinical study of a test that screens an egg for chromosomal abnormalities - the main cause of non-viable embryos during IVF - has been conducted. This may help pave the way for women with a history of IVF failure to achieve successful pregnancies.

The test is called comparative genomic hybridisation (CGH) and is designed to examine polar bodies for abnormalities. Polar bodies are discarded chromosomes that mirror the chromosomes of the egg. Polar body one's chromosomes are discarded from the egg. Polar body two's chromosomes are discarded later on from the zygote.

CGH has been used in clinics to test only the first polar body. In this study of 41 women - which has led to the birth of a number of healthy babies in Bonn, Germany, and Bologna, Italy - scientists biopsied the first and second polar bodies to see if testing both leads to more accurate results.

The analysis of polar body one detected 72 percent of all abnormal eggs, but adding the analysis of the second polar body significantly improved the detection rate up to 89 percent.

'The pilot study was aimed at answering one of the most pressing questions in assisted reproduction: how can we improve the success rate of IVF treatments in women of advanced maternal age?' said Professor Joep Geraedts, past chairman of the European Society of Human Reproduction and Embryology (ESHRE), which funded the study.

Unlike other screening methods, CGH tests all 23 pairs of chromosomes and the egg at fertilisation, rather than the developing embryo. By selecting an embryo that has the best chance of developing into a live birth, IVF doctors are less tempted to implant multiple embryos. Twins and triplets are at risk of low birth weight and developmental difficulties.

'For those working in the field, the study is really interesting', said Dr Alan Thornhill, Scientific Director of the London Bridge Fertility, Gynaecology and Genetics Centre.

Plans are being laid for a large-scale international clinical trial in 2011, ESHRE said. Experts say if CGH screening proves successful in larger trials, it may be used to help women over the age of 37 who undergo IVF, or those with a history of miscarriage or a record of unsuccessful IVF treatments. All these conditions are associated with a higher than average rate of embryonic chromosomal abnormality.

But doctors involved in the trial stress the technique can only help them identify viable eggs - it does nothing to improve the chances of producing high-quality eggs in the first place.

SOURCES & REFERENCES
A double first: the first babies born in the world's first study to assess comprehensive genetic screening before IVF
AlphaGalileo |  15 October 2010
Babies born following IVF with arrayCGH genetic egg screening
PHG Foundation |  21 October 2010
First babies born in IVF full gene screening study
Reuters |  15 October 2010
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