British scientists have developed a new technique that could improve the chances of having a baby for thousands of couples undergoing fertility treatment. One of the main stumbling blocks with in vitro fertilization (IVF) is choosing which test-tube embryos will be most likely to implant in the womb and result in a pregnancy.

Fertility experts examine each embryo under a microscope to choose the best ones, but the method is only modestly successful. Less than 20% of IVF treatment cycles in Britain result in a live birth. Professor Henry Leese said on Friday that a technique he devised with colleagues at the University of York in northern England could remove much of the guesswork. "The problem has always been how to choose the best (embryo) to transfer," he said in an interview.

"The technique 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 birth." So far it has only been tested in the laboratory but if clinical trials, which Leese hopes to begin in six months, are successful it could be available in about three years.

The technique involves placing a two-day old embryo, about the size of a pinhead, in a tiny drop of solution containing amino acids that mimics the concentration that would be found in the womb. Amino acids are compounds essential for life. After about 24 hours scientists analyze a sample of the solution to see how much of the amino acids were taken up by the embryos "We found that embryos that had a lower take-up or consumption of amino acids developed successfully to the stage at which you would transfer them," Leese said in an interview. "The quieter embryos are best," he added.

Leese said the method is completely non-invasive and does not harm the embryos in any way. More than one embryo is usually implanted in the womb to improve the chances of achieving a pregnancy, but this also increases the risk of multiple births, which can be dangerous for the mother and babies. "We're aiming, down the line, for clinics to transfer one embryo," said Leese, whose research is published in the journal Human Reproduction.

Improving confidence in embryo selection could reduce the need to transfer multiple embryos to the womb. Fertility treatments could ultimately become cheaper; women may not need to take as many drugs because they would not have to produce as many eggs for each treatment cycle. Fertility treatment is one of the fastest growing areas of medicine. About one in seven couples seek help for infertility.