A fertility test that measures the viability of eggs in a woman's ovaries may soon give women the ability to tell the time on the proverbial biological clock. The test is the result of six years of work by Oxford scientists who discovered that levels of the hormone, inhibin B, are related to whether a woman's ovaries can release eggs healthy enough for fertilisation.

Gillian Lockwood, an infertility research fellow at John Radcliffe Hospital, began her research in this area as a result of observing some young women repeatedly fail at conventional IVF treatment. Her study showed that in a large group of women undergoing IVF, those who conceived had inhibin B levels that were comparable with those of women from the study's fertile control group. Women who failed to get pregnant had very low levels of the hormone. It is known that women's ovaries age at different rates from the rest of their bodies.

'The test will allow women to maximise the choices they make during a relatively narrow window of their reproductive life-span', said Lockwood. 'Those who do decide to delay childbearing will be able to do so with some sense of security.'