The test boosts the odds of success
A screening technique can double the chance of IVF success, giving hope to tens of thousands of women struggling to have children, say experts.
Doctors at an annual US fertility meeting heard for the second year running of the merits of a test that screens embryos for genetic faults.
So far more than 20 babies have been born using the technique.
The UK researchers say they are now able to back the method with "great confidence".
They hope it will eventually be available to all. Currently, it is offered in a few private UK clinics.
Doctors believe the £2,000 test, called comparative genomic hybridisation or CGH, will be particularly useful to older women, whose embryos have a greater risk of carrying genetic errors that cause conditions like Down's syndrome.
The screening checks chromosomes in the developing embryo when it is a few days old, meaning only those embryos with the best chance of success are used in fertility treatment.
Dr Dagan Wells from Oxford University, who led the study, described the latest results on 115 women - six times as many as last year - as "astonishing".
The results are particularly impressive as many of the women were on their "last chance" at IVF - they were typically aged 39 with two failed IVF cycles behind them.
Raising the odds
In total, 66% of the women fell pregnant after screening - more than double the number (28%) who typically fall pregnant without it.
Dr Wells told the American Society of Reproductive Medicine's annual conference: "We were taken aback by the impact it had on the success rates.
"I think it's at the point now that we can say with great confidence that we are seeing a positive effect of this."
Around 37,00 women undergo IVF every year in the UK and less than one in four of these procedures is successful.
Allan Pacey of the British Fertility Society said: "Embryology is really crying out for something like this.
"We really haven't moved on from the science of just looking down the microscope and seeing if an embryo looks good on the basis of some rather loose criteria."
Susan Seenan, from Infertility Network UK, said: "We welcome all new research which may ultimately improve the success rates of IVF for patients.
"Although this is still in very early stages, it could be of great benefit to older women whose chances of success with IVF treatment is lower and it is also welcome given the move towards single embryo transfer in the UK and the lack of NHS funding which often, unfairly, means that patients are being denied access to the three cycles which the NICE guidance recommended in 2004.
"Improvements in success rates are always important but even more so where patients are receiving only one, or in some cases, no NHS cycles, and we look forward to seeing if further research confirms these results."