A test that predicts the success of second attempts at in vitro fertilisation (IVF) treatment with 1000 times more accuracy than the existing approach has been developed.
Experts believe the patented test could help couples decide if it is worth another try at IVF after an initial failure.
About three quarters of IVF treatments fail to produce a pregnancy.
Currently, age is used as the starting point for advising patients on the likely outcome of IVF.
A woman of 38 might be told she has a 33 per cent chance of becoming pregnant with IVF but the odds are lengthened if she is low on eggs.
The new test is said to be 1000 times more accurate than age-based guidelines.
However, since it relies on data from a first IVF treatment cycle, it can only be used to predict the success or failure of a second treatment.
The procedure, developed by Dr Mylene Yao and a team of researchers at Stanford University, California, effectively turns the initial cycle into a prognostic test.
Writing in the journal Proceedings of the National Academy of Sciences, the scientists concluded: "Our findings show that the first IVF cycle can provide quantitative, customised prediction of the live birth probability in a subsequent cycle.
"This concept is radically different from the current paradigm, in which age is a major predictor."
Stanford University holds a patent on the test and a spin out company called Univfy has been formed to develop and market it.
The scientists analysed data from 1676 IVF treatments performed at Stanford between 2003 and 2006 and identified 52 factors that influenced a woman's chances of having a baby.
As well as age, they included levels of certain hormones, the number and quality of eggs, and embryo characteristics.
A computer model was developed that used the information to sort patients into different sub-groups according to their subsequent IVF success.
In 60 per cent of cases the model's predictions varied significantly from those based on age alone - and more than half of these showed an improved chance of having a baby.
The findings indicated that relying on age alone "may provide misleading live birth outcome probabilities for a large portion of patients", said the researchers.
Co-author Dr Lynn Westphal, from Stanford's Reproductive Endocrinology and Infertility Centre, said a woman's decision to repeat IVF was influenced by a number of factors including cost and the chances of becoming pregnant.
"Many patients, even if they have insurance coverage, will drop out - either because they don't understand what their odds are or they find it's a very emotionally challenging experience to go through."
