Scientists have found a possible explanation for why women lose their fertility in middle age in a discovery that could pave the way for treatments to extend women’s childbearing years beyond what is naturally possible.

In a series of experiments on eggs from women receiving fertility treatments, researchers learned that the function of several DNA-repair genes weaken with age.

This decline is accelerated in women near the end of their childbearing years, according to the results in Science Translational Medicine.