A long-held belief about women and fertility is that each woman has a set amount of eggs in her lifetime and that when those eggs are depleted at menopause, so are her chances at having a biological child. However, research out of Massachusetts General Hospital questioning that view. Using stem cells taken from human ovaries, scientists have produced early-stage eggs, which brings up all sorts of questions about possible new methods for treating infertility. Nicholas Wade, writing in the New York Times, adds, "The ability to isolate stem cells from which eggs could be cultivated would help not only with fertility but also with biologists’ understanding of how drugs and nutrition affect the egg cells."

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Jonathan Tilly, the director of Mass General's Vincent Center for Reproductive Biology and leader of the new research, had reported in 2004 that ovarian stem cells in mice could create new eggs "similar to how stem cells in male testes produce sperm throughout a man’s life." His new study attempted to prove this with humans. Researchers took healthy ovaries from patients having sex reassignment surgery, and injected stem cells from the ovaries into human ovarian tissue grafted under the skin of mice: "Within two weeks, early stage human follicles with oocytes had formed." Ryan Flinn writes in Bloomberg Businessweek that this could potentially point at "new ways to aid fertility by delaying when the ovaries stop functioning." 

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Dr. Tilly has long been a proponent of the belief that women might be able to produce new eggs, and has said the 50-year belief otherwise is based on lack of evidence rather than on data proving that it's impossible. In 2005, he reported that women have a "hidden reserve of cells in the bone marrow that constantly replenish the ovaries with new eggs," though other researchers have not been able to confirm his finding. 

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Along with opening new doors to understanding the incredibly complex human egg cell, this new research could eventually have very practical implications for the 10 percent of child-bearing age women in the U.S. who have fertility problems. More philosophically, it opens up a new way of thinking about the hard-stop in women's lives for having kids. While fertility technologies like in-vitro and egg freezing are happening to some extent, Tilly's team is exploring the way this new knowledge could improve in-vitro -- IVF involves a limited number of eggs -- and also looking into possibility of developing an ovarian stem-cell bank with eggs that could be "cryogenically frozen and thawed without damage, unlike human eggs." 

“The problem we face with IVF is we don’t have many eggs to work with,” said Tilly. “These cells are renewable. If we are successful -- and it’s a big if -- in generating functioning eggs from these cells, we can generate as many eggs as we need to on a per patient basis.”

Researchers warn that there's a ways to go before there are any real applications to this, if ever. Female reproduction expert David Albertini said it's still unclear whether the egg cells yielded actually could be used in human fertility. Cells grown in laboratories are more likely to develop abnormalities; even if they are proven viable, it's a given that there will be numerous social and political aspects that factor in down the road. Nonetheless, evidence that women's eggs may not be the finite commodity we all thought they were seems poised to make a huge impact across many aspects of contemporary life. What would if mean, for instance, if the old ticking "biological clock" no longer applied -- or applied to women and men more equivalently? 

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As Tilly said in a recording released to the press, "If we can guide the process correctly, I think it opens up a chance that sometime in the future, we might get to the point of actually having an unlimited source of human eggs. A woman could come in, have a small biopsy taken from her ovary for us to retrieve these cells. Once we get these cells out, we can take a hundred of them and make a million of them. If we can get to the stage of generating functional human eggs outside the body, it would rewrite essentially human assisted reproduction."

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Brave new world? Maternity ages stretching into the 50s and 60s? Or simply another step toward the prediction some have made that sex will be just a recreational activity in another 10 years?

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New Stem Cell Research Could End the Hard Stop of Female Fertility