Researchers anticipate higher IVF success rates
Two British scientists have made a major advance in assisted reproductive techniques, which could ultimately lead to an improvement in IVF success rates. Research has allowed Dr Dagan Wells and Professor Joy Delhanty of the University College London Medical School to check the copy number of all the chromosomes in virtually every cell of a test-tube embryo. Full chromosomal analysis has not been possible up until now as existing technology has restricted analysis to a small number of chromosomes per cell. Most studies have only succeeded in testing five of the 24 different types of chromosomes present in a cell, but Dr Wells and Professor Delhanty have developed a new technique, which combines whole genome amplification and comparative genomic hybridisation, allowing the assessment of the copy number of every single chromosome in the majority of cells. There is evidence that chromosomal abnormalities play a major role in early failure and miscarriage. The ability to detect which embryos are chromosomally 'normal' will eventually allow doctors to transfer only those embryos with the best chance of forming viable pregnancies. The scientists' results have also led to another major discovery: the number of human embryos that are completely 'normal' is actually very low. Only three out of 12 embryos studies 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. This finding supports previous studies, which have indicated that most human embryos contain a proportion of abnormal cells. '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 considerable less than those of a chromosomally normal embryo', said Dr Wells. 'We hope that 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.' Professor Delhanty added that they are currently working on the next step, that or reducing the length of the procedure so that it can be applied not only in routine IVF, but also in preimplantation genetic diagnosis 'where accuracy is even more important because it involves couples already at high risk of passing on serious inherited conditions.' The technique could be available in many specialist IVF clinics within a few years for high-risk patients. The technique is also likely to find application in several other fields, including cancer research, forensics and the analysis of ancient DNA samples.