Women who go through early menopause and are unable to have children have been given fresh hope after scientists found a way of "restarting" ovaries.
The study could pave the way for women to one day conceive even though they have gone through the menopause at an early age.
Premature ovarian failure affects 1% of women under 40, and one in 1,000 (0.1%) under 30. The normal age for menopause is debatable but experts consider early menopause as before 45.
Possible reasons include chromosome abnormalities, such as Down's syndrome; enzyme deficiencies, which can damage eggs and prevent the production of the hormone oestrogen; and autoimmune diseases, where the body effectively turns on itself.
Scientists at the World Congress of Fertility and Sterility in Munich said the latest work on rats could offer hope for the future.
A team from Cairo University used stem cells to restore ovarian function in a group of 60 female rats. The rats were divided into four groups, with the first not given any treatment and acting as a control.
Rats in all the other groups were treated with a chemical to stop their ovaries working, with those in the second group then given injections containing stem cells.
Group three was injected with a saline solution to act as a control, and the group four rats had ovarian failure but received no treatment, also enabling them to act as a control.
The Cairo team tested the hormone levels of all the rats to see if they returned to normal following treatment.
Within two weeks, the rats in group two, which had been treated with stem cells, had regained full ovarian function.
After eight weeks, their hormone levels were the same as rats who did not have ovarian failure.
Male stem cells were used so researchers could confirm their presence in the ovaries of the treated group by searching for the Y chromosome.
Professor Osama Azmy, who led the study, said: "The treated ovaries returned to producing eggs and hormones, and we could detect the presence of the stem cells within the newly functioning ovaries.
"What we have done is proven that we can restore apparently fully functioning ovaries in rats. The next step is to look how these rats might reproduce, and to characterise the chromosomes of offspring following treatment.
"We have not yet reached the stage of producing offspring, and so we will need to understand if the baby rats will be genetically related to the mother, or to the donor of the stem cells.
"This is proof of concept and there is still a long way to go before we can apply this to women.
"Nevertheless, this work holds out the possibility that women with premature ovarian failure might be able to bear a baby of their own."
