Early stage human eggs have been developed from stem cells for the first time, US researchers have revealed.
The scientists looked at cells found on the surface of ovaries
The researchers from the University of Tennessee claim the laboratory research could help women with premature menopause or fertility problems.
And they suggest in Reproductive Biology and Endocrinology that it could lead to the natural menopause being delayed by up to 12 years.
But a leading UK expert cautioned the work was still at a very early stage.
Women have around two million egg-producing follicles in their ovaries when they are born.
But by the time they reach puberty the number has fallen to about 400,000.
The number of follicles continues to fall until her menopause, at which point she will no longer be able to produce a mature egg capable of being fertilised.
However the Tennessee researchers found ovarian stem cells could develop into new eggs.
They took ovarian surface epithelium (OSE) cells from the outside of the ovaries of five women aged 39 to 52.
They were then grown in a lab for five to six days. Some were exposed to a growth-stimulating oestrogen medium called phenol red.
Those cells which were cultured without this medium differentiated into immature small cells of various different types.
But those exposed to phenol red completed the first stage of the division needed to become mature human eggs, capable of being fertilised and developing into an embryo.
They went on to become mature human eggs capable of being fertilised and developing into an embryo.
The team say the OSE cells can be easily harvested from the surface of the ovaries, using a laparoscope, a flexible telescope-like instrument.
They said the discovery could help those women with poor fertility or who are set to go through an early menopause, who lack follicles in their ovaries, to have a better chance of conceiving through IVF.
They predicted that eventually, frozen OSE cells from younger women could be preserved for later production of fresh eggs, potentially preventing the risks linked to pregnancies in older women which naturally have to use mature eggs.
And being able to produce new egg and granulosa stem cells may enable the development of new ovarian follicles.
The team claim this could lead to a 10- to 12-year delay of the onset of natural menopause.
Professor Antonin Bukovsky, who led the research and is editor-in-chief of Reproductive Biology and Endocrinology, wrote: "Development of numerous mature oocytes (eggs) from adult ovarian stem cells in vitro (in the laboratory) offers new strategies for the egg preservation, IVF utilisation, and treatment of female infertility."
They added that fertilised laboratory-grown eggs could also provide embryonic stem cells for other medical applications and basic research.
Dr Simon Fishel, director of Care Fertility, told BBC News Online said: "This research is at a very early stage and needs to be confirmed.
"Other research has shown it's very difficult to get eggs that exist at an immature stage to become viable. And here, we're going back an enormous stage before that."
But he added: "If it is confirmed, it is possible that it could help pre-menopausal women and women coming up to their menopause having IVF, who currently have to use egg donors.
"This could mean they could have a baby using their own genetic material."