Scientists have used stem cells to grow healthy human eggs for the first time, a development they believe will usher in new fertility treatments and enable women to delay menopause by a decade.
A shortage of donors means new sources of eggs are desperately needed by fertility clinics to help women trying for babies through IVF.
The research suggests that a near limitless supply of eggs could be produced by taking a woman's own stem cells and growing them into eggs in the lab.
Professor Antonin Bukovsky, a researcher at the University of Tennessee in Knoxville, who led the work, says his finding shows that women are capable of producing new eggs later in life, rather than being limited to the quota they are born with.
At birth, a woman's ovaries typically contain around 2m egg-producing follicles, falling to around 400 by the time she reaches puberty.
The number continues to fall until menopause, when too few exist for her to become pregnant.
According to Prof Bukovsky, his work could lead to advances in fertility treatment that would allow women to grow and store their own viable eggs, so they can delay having a family until an older age.
The stem cells could also be used to rejuvenate ageing ovaries, with the potential of delaying menopause for 10 to 12 years.
In the study, which is published in the journal Reproductive Biology and Endocrinology, Prof Bukovsky's team collected cells from the surface of ovaries in five women aged 39 to 52. They then tried different strategies to grow the cells in dishes over five to six days.
The researchers found that cells grown in the presence of the growth-stimulating hormone oestrogen transformed into large egg-like cells, which later became mature human eggs capable of being fertilised.
Robert Winston, a fertility expert based at Hammersmith hospital, said the achievement was highly important, if it was proved to work: "If they've really done this, it would be extraordinary. There is such a shortage of eggs, it's incredibly important." Significantly, harvesting eggs from the outer surface of ovaries is a straightforward procedure, and can be done using a common flexible instrument called a laparoscope.
The use of stem cells to prolong the life of ovaries and so delay menopause was also a significant advance, Prof Winston added. "There'll be a demand for it, particularly from professional women who want to pursue their careers," he said.
Prof Bukovsky's team is now planning to test whether the stem cells they collected from women's ovaries can withstand being frozen. "Once we've frozen them, we'll thaw them out and see if they still work. If we can preserve them effectively, women could have them stored for 20 years," he said.
If the next experiments are a success, thawed stem cells taken from a woman's own ovaries could be transformed into fresh eggs in the lab whenever they are needed. "This could extend fertility to the age of 60," Prof Bukovsky said.
Because the eggs are created just before use, they are less likely to be damaged or worn, as typically happens to eggs that remain in a woman's ovaries for long periods of time.
Scientists also revealed yesterday they have uncovered a new clue to the mystery of implantation - the process by which an embryo becomes wedded to the womb.
Implantation is the last step in the chain of events between fertilisation and pregnancy, and one of the least understood. If an embryo does not properly attach itself to the wall of the womb it cannot develop into a viable foetus.
Scientists reported in the journal Nature yesterday how they identified a certain type of protein that appears to play a crucial role in implantation. The discovery may lead to treatments for some of the 20% of infertility cases that are currently unexplained.
