Breakthrough by British scientists may improve IVF success rate

UK scientists have devised a method of checking for chromosomal abnormalities in an embryo which they believe could improve women's chances of having a baby through fertility treatment.

Many miscarriages and conception failures are thought to be due to abnormal chromosomes in the embryo. Human reproduction is remarkably inefficient compared with some mammals. Couples trying for a baby have only a 25% chance of a successful pregnancy, even though there is a 60% chance that the egg will be fertilised. In IVF, the success rate ranges around 20% to 30% per treatment cycle, even though two to three embryos are returned to the womb.

Healthy cells contain 23 pairs of chromosomes, 22 of which are identical in both sexes. But sometimes one or more chromosomes might be missing, or an additional copy added. Chromosomes may also be broken, or fused together.

Dagan Wells and Joy Delhanty, from University College London Medical School, have used DNA cloning techniques to copy and "amplify" every chromosome in a cell. Until now, the best doctors had been able to do was to assess the state of up to about eight chromosomes.

Their hope is that IVF clinics may be able to use the technique to screen embryos produced during fertility treatment. Those with the most "normal" arrangement of chromosomes would be put into the womb and, they believe, would stand a better chance than the rest of implanting and developing into a healthy baby.

But yesterday Lord Winston, one of the UK's top embryologists, cast doubt on the chances of it improving IVF success rates. He said it would not be easy to adapt it to the clinic and that women should not raise their hopes prematurely.

Dr Wells and Professor Delhanty will present their study to the American Society for Reproductive Medicine's annual meeting in San Diego, California, where they have been awarded the conference prize.

The technique was tested on 12 embryos donated by IVF patients, from which 64 individual cells were separated and analysed. At this stage of development, a human embryo consists of only about six to eight cells. They were surprised to find that only three of the embryos studied had the correct number of chromosomes in every cell. Nine contained at least one abnormal cell, and three of those contained no normal cells at all. They conclude that it is not necessary for an embryo to have a perfect set of chromosomes to develop into a healthy baby, but that those whose chromosomes are the closest match to normality stand the best chance.

But Lord Winston disagrees, pointing out that "mosaicism" - chromosomal variation between different cells - occurs quite frequently. The state of one or two cells does not necessarily reflect the health of the rest of the embryo, he said. He also pointed out that at present the technique took too long to be of practical use.