US scientists have gained greater insight into how ageing affects the ovaries and hope the understanding will lead to treatments to improve fertility.

Scarred and inflamed ovaries may be causing infertility in older women, a new study suggests.

Scientists in the US have found the ovarian stroma - the environment in which the eggs grow in - of older mice look completely different to those of young mice.

It's hoped this new understanding of how ageing effects the ovary will lead to new treatments to preserve fertility and help young women with polycystic ovary syndrome.

Under the microscope, the ovarian stroma of the older mice appeared fibrotic and inflamed.

Such an environment is likely to decrease the production of healthy eggs.

"There is no way this environment won't impact the eggs growing in it and it very likely contributes to their decrease in quality, said lead author, associate professor Fancesca Duncan from the Center for Reproductive Science at Northwestern University Feinberg.

It's widely known that the number and quality of eggs a woman's ovaries produce deteriorate significantly after the age of 40 but this is the first study to reveal what happens to the ovarian environment as a woman ages.

"Our work establishes fibrosis and inflammation as hallmarks of the ageing ovary and lays the foundation for considering the use of anti-fibrotic or anti-inflammatory treatments to delay or counteract the impact of reproductive ageing," said Duncan.

Duncan says the findings, published in the journal Reproduction, also have broader implications for women with polycystic ovary syndrome, a common endocrine system disorder among women of reproductive age that causes fibrosis of the ovary.