Science may soon be able to predict more accurately how long a woman will remain fertile.

A survey of healthy women carried out at the University of St. Andrews and by experts from both the University of Edinburgh and University of Glasgow, all in the U.K., has revealed the normal range of levels of a hormone considered vital to a woman’s fertility.

The survey showed the normal range of levels of the anti-Mullerian hormone (AMH) in relation to age. This hormone reflects the activity of the ovaries during a woman’s lifetime and gives an estimate of her remaining egg supply.

The study looked at 3,200 samples from healthy girls and women to find out the average levels of AMH. The findings will now allow fertility experts to tell how a women’s AMH level compares with the average for her age.