College of Medicine & Veterinary Medicine

Study tracks speed of biological clock

Women lose almost 90 per cent of the eggs in their ovaries before the age of 30, a new study has shown.

The mathematical model shows that the average woman has only 12 per cent of her eggs left by the age of 30 and only three per cent by the age of 40.

It provides further evidence that women are born with a fixed number of eggs, which declines with increasing age.

Researchers hope it will be useful in predicting the age of menopause in healthy women and it may also help to preserve the fertility of women who undergo cancer treatment.

International study

It is known that women are born with a supply of millions of eggs in their ovaries and that over time the number of eggs decreases until menopause.

The study, using data from women in the UK, US and Europe, tracked the development of a woman’s egg supply and found that it peaks at about 20 weeks after conception - while she is still in her mother’s womb.

From then, it declines until no eggs are left usually around 50-51 years.

By understanding the dynamics of ovarian reserve, we can predict which children and young people treated for cancer are most at risk of an early menopause. These patients may benefit from having their eggs frozen before cancer treatment starts.

Dr Hamish WallaceConsultant Oncologist and Reader at the University

Dr Tom Kelsey who worked on the project at the University of St Andrew’s explained, “At around the age of 14, something happens that we’ve never seen before: the rate of recruitment of immature eggs towards mature eggs drops off and we don’t know why. Of course at that age there are a lot of hormonal changes that might account for this new observation”.

The research is funded by the Wallace-Kelsey Research Foundation Trust and is published by PLoS One.