Why does female fertility fall with age?

It's a well-known fact that, as a woman ages, her chances of falling pregnant drop. And this seems to be driven by a fall in the quality of the eggs that she produces. Why this happens though, in an otherwise healthy individual, is a mystery. Now Francesca Duncan, who studies female fertility at Northwestern University, has discovered that older ovaries contain large amounts of fibrous tissue produced by inflammation, and this appears to be harming the ability of the ovary to nurture healthy eggs.