Fertility study measures speed of our biological clock

New evidence suggests a woman’s egg supply peaks some 20 weeks after conception, while still in the womb, and gradually declines for around 50 years, according to a study published in an online science journal.

The collaborative project between researchers at the University of Edinburgh and the University of St Andrews has led to an improved understanding of the way in which the female ovarian reserve—the number of eggs a woman has in her ovaries—declines over time.

The research published in the flagship open-access online journal Public Library of Science (PLoS) provides further evidence to support the theory that women are born with a fixed number of eggs, which drops over time.

Dr Tom Kelsey, a senior researcher at the School of Computer Science at the University of St Andrews said: “Previous models have looked at the decline in ovarian reserve, but not at the dynamics of ovarian reserve from conception onwards.

"Our model shows that for 95 percent of women, by the age of 30 years, only 12 percent of their maximum ovarian reserve is present, and by the age of 40 years only 3 percent remains.”

The study was funded by the Wallace-Kelsey Research Foundation Trust, and was a collaboration between Dr Kelsey and Dr Hamish Wallace, consultant oncologist at the Royal Hospital for Sick Children and Reader at the University of Edinburgh.

Dr Wallace said: “Our model provides no evidence for the presence of stem germ cells in the ovary that could increase the number of eggs present in the ovary and delay the menopause.”

Data was collected from women in the UK, US and Europe and formed the basis for a computer model, the first of its kind to model ovarian reserve from conception.

It is hoped the research could help predict the onset of menopause in healthy women, and may also help in preserving the fertility of women and girls undergoing treatment for cancer.

Dr Wallace told The Journal that the project represents an extension of research looking at the sensitivity of human egg cells to radiation, which is commonly used in cancer therapies.

“A better understanding of the dynamics of ovarian reserve will help us to 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.”