Women hoping to have a baby through fertility treatment can from today use an online calculator to show them how likely they are to succeed.
IVF (in-vitro fertilisation) is expensive, only sometimes available on the NHS and less successful than many people think.
To help couples to decide whether IVF is worth pursuing for them, academics at Glasgow and Bristol have created the calculator, which they say will predict a woman's likelihood of giving birth with up to 99% accuracy.
"In the US and the UK, IVF is successful in about a third of women under 35 years old, but in only 5%-10% of women over the age of 40," said Professor Scott Nelson, Muirhead chair of reproductive and maternal medicine at the University of Glasgow.
"However, there are many other factors in addition to age which can alter your chance of success, and clinics don't usually take these into account when counselling couples or women."
The calculator, available for free at ivfpredict.com, is based on data from more than 144,000 IVF cycles held by the Human Fertilisation and Embryology Authority (HFEA) – all the outcomes of treatments undergone between 2003 and 2007.
"Essentially, these findings indicate that treatment-specific factors can be used to provide infertile couples with a very accurate assessment of their chance of a successful outcome following IVF," Nelson said.
"It provides critical information on the likely outcome for couples deciding whether to undergo IVF. Up until now, estimates of success have not been reliable.
"The result of this study is a tool which can be used to make incredibly accurate predictions."
To use the calculator, nine questions must be answered. It will ask the woman's age, how many years she has been trying to get pregnant, what doctors say is the cause of her infertility, what previous IVF attempts she has made and what were the outcomes.
Debbie Lawlor, professor of epidemiology at the University of Bristol, said the calculator would be of use not only to couples but also to "healthcare funders like the NHS to ensure appropriate use of resources". It raises the possibility that GP consortia could turn couples down for NHS treatment on the basis that their chances of success are too low.
The findings, which are published in the Public Library of Science, were welcomed by Professor Gordon Smith, head of the department of obstetrics and gynaecology at Cambridge University.
"There is a real need in medicine to try to replace general statements such as 'high risk' and 'good chance' with well validated, quantitative estimates of probability, such as we have with Down's syndrome screening," he said.
"This model for predicting the outcome of IVF has exploited a valuable collection of routinely collected data, applies sophisticated statistical modelling and the output provides women considering IVF with an understandable and quantitative estimate of their chances of success. It is a great resource."
