Embryo screening test boosts success rate of IVF pregnancies

Technique pioneered in Britain doubles likelihood of pregnancy, study suggests

A British test for screening the quality of IVF embryos has significantly improved the chances of a successful pregnancy, according to the results of a preliminary trial carried out on American women.

A study of more than 500 embryos from 115 women undergoing IVF treatment found that the screening test for abnormal chromosomes could double the number of women falling pregnant compared to normal IVF treatment.

The screening test is usually carried out on IVF embryos at the blastocyst stage of development, at five or six days after conception. A single cell is taken from the embryo and analysed by a new technique for identifying an abnormal number of chromosomes, with the aim of picking the best-quality embryos for transfer into the patient's womb.

About half of all IVF embryos are thought to suffer from an abnormal number of chromosomes and the new technique of comparative genomic hybridisation (CGH) can scan all 23 pairs of chromosomes for any that are missing or duplicated.

Results released at the annual meeting of the American Society for Human Reproduction in Atlanta, Georgia, showed that two thirds of the women involved in the study became pregnant after CGH screening, compared to the normal rate of less than 30 per cent who fall pregnant after IVF treatment.

Dagan Wells of Oxford University said that the latest findings were "astonishing" but warned that the results could be affected by a bias in the study, as most of the women in the study had more than one embryo transferred to increase the chances of a pregnancy, and the embryos had already reached the blastocyst stage.

"We are skimming the cream off the top in the likelihood of success. Even though our results are biased towards those women with blastocysts, the results are astonishing. The thing that's got a big impact for us in the UK is that the implantation rate is high – that's the probability of one embryo becoming a baby," Dr Wells said. "Our results show that, after this test, if we transfer one embryo, we would expect two-thirds of women to get pregnant."

The technique would offer hope to older women, but could also be useful for those who are younger. "We have not done this test with younger patients because we know that the risk of chromosomal abnormality in embryos increases with age," he said. "However, this technique may well help younger women because it virtually eliminates the risk of conditions like Down's. The test has accuracy in excess of 95 per cent.

"If these results are replicated – particularly in a randomised control trial – then there would be an argument for making this the standard of care. This would have huge emotional implications for patients and financial implications for the NHS."

CGH costs about £2,000 on top of the normal fee for IVF. In September, experts in Nottingham used a similar technique called array CGH to examine eggs rather than embryos. Baby Oliver, the first child born as a result, came after his parents had suffered 13 previous failed IVF attempts.