Screening picks 'best chance' embryos

Embryos may have genetic imperfections

A technique which can examine all the chromosomes in a test-tube embryo could identify those with no chance of growing.

A great many human embryos are 'non-viable' - if they implant in the womb, either after natural conception, or as a result of IVF, they will not mature into foetuses.

These pregnancies are likely to result in miscarriage, often at a very early stage.

Fertility treatments fail formany patients

In IVF, doctors must pick two, or at most three embryos to be implanted.

They have various criteria for assessing the viability of embryos, but even using these, the chances of a pregnancy occurring are relatively low.

The new work, carried out at University College London Medical School by Dr Dagan Wells and Professor Joy Delhanty, could offer another technique for working out which embryos are most likely to develop correctly.

And it also offers the possibility of pre-implantation genetic screening of embryos for various diseases which have a genetic aspect.

Whole genome

The UCL team have been working on a method of examining the whole genome - every single chromosome - of the embryo.

Until now, the most sophisticated technique has only been able to examine some five out of 24 different types of chromosome.

The researchers examined 12 embryos donated by patients undergoing IVF - examining a total of 64 individual cells.

They found that there were very few embryos which were chromosomally normal. Only three had the correct number of these in every cell.

The remainder had at least one abnormal cell - three had no normal cells at all.

Dr Wells said: "Having a small number of abnormal cells does not automatically mean an embryo will fail to implant or that there will be a miscarriage.

"However, the evidence suggests that the chances of such an embryo forming a successful pregnancy are considerably less than those of a chromosomally-normal embryo.

"We hope the new technique will help embryologists to decide which embryos are the most likely to implant and develop normally.

"By preferentially transferring these embryos considerably higher success rates for couples undergoing IVF may ultimately be achieved."

IVF expert Dr Simon Fishel told BBC News Online that the UK Human Fertilisation and Embryology Authority had to be prepared to allow selected embryos to be implanted so the next step could be taken.

He said: "Unfortunately in some areas we have become also-rans - when one goes to international meetings it's noticeable how much heavyweight clinically-based research is being done in other countries."

The resaerch was published in the journal Molecular Human Reproduction.