We hope to have a diagnostic test for use in clinics in two or three years' time

Professor Henry Leese, University of York

At the moment, potential embryo implants are assessed under a microscope to see if they have the potential to develop inside the womb.

However, this procedure has not proved particularly successful in helping women to become pregnant.

Laboratory tests

Under this new method, embryos are placed in a culture medium containing amino acids two days after they have been fertilised.

They are then monitored in a laboratory to see how they consume or produce these amino acids.

Writing in the journal Human Production, scientists said the performance of the embryos in the culture medium helps them to determine which embryos are most likely to result in a successful pregnancy.

Professor Henry Leese, from the University of York, said the method could be used in clinics within a few years.

"We've found a marked difference between the embryos which develop successfully in culture and those which do not. The healthy embryos have a 'quieter' metabolism," he said.

"The method is completely non-invasive and does not harm the embryos in any way. It opens up the prospect of selecting high-quality embryos to replace into the womb, increasing success rates, reducing the financial and emotional cost to patients and greatly eliminating the risk of multiple births.

"If all goes well with the clinical trials, we hope to have a diagnostic test for use in clinics in two or three years' time."

Promising

Lynn Fraser, professor of reproductive biology at Guy's, Kings and St Thomas's School of Biomedical Sciences, said the findings were "interesting and promising".

But speaking to BBC News Online, Professor Fraser said that even if the method was generally available it would not ensure a successful pregnancy.

She said: "It is not a guarantee but it has a biologically sound basis."

Professor Fraser added that the scientists would have to develop a user-friendly system for identifying which embryos were most likely to survive.

"The crucial thing will be whether or not they can develop some product that can be very easily used. The techniques they used in the study were very sophisticated," she said.