The first trial of a procedure which selects IVF embryos with the best chance of developing into healthy babies was presented last week at the American Society for Reproductive Medicine conference in San Francisco. Dr Dagan Wells and colleagues at Oxford University, UK screened embryos for 23 women before implantation and showed a much improved success rate of IVF; 18 out of the 23 women have either already given birth or have passed the point in pregnancy at which miscarriages typically occur.

The embryo quality test, which uses a technique called comparative genomic hybridisation (CGH), means embryos' chromosomes can be more comprehensively screened for abnormalities. This is not the first pre-implantation genetic test to be developed but Dr Wells' test screens embryos at a later stage of pregnancy (when the embryo is five days old and has more than 100 cells). This means that every chromosome pair in the embryo can be examined and, since more cells can be removed for analysis, it yields more accurate results.

The 78 per cent success rate reported by Dr Wells and colleagues is significantly better than the rate usually achieved (60 per cent) in a patient group like this who have all had unsuccessful IVF treatment previously and have an average age of 37. Following CGH screening, the implantation rate for each individual embryo is 62 per cent - the normal rate is 28 per cent. Dr Wells said, 'The pregnancy rates we've got so far are absolutely phenomenal. The probability that one embryo leads to a pregnancy is doubled. That means that you've got a much better chance of a pregnancy if you do a single embryo transfer.'

Dr Wells and colleagues are now ready to begin a larger scale trial in the UK and have applied for permission from the Human Fertilisation and Embryology Authority (HFEA, the fertility watchdog) to offer the test to patients at the Oxford Fertility Unit. It is anticipated that the test would add around £2000 to the present £4000 cost of IVF treatment.