Want to become a mum at 60? Scientists test boundaries of fertility

Sun Mar 14, 2004

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PARIS (AFP) - Once upon a time, women faced a biological clock, which tick-tick-ticked away the years of their fertility until it rang, with a dull and often dreaded clang, in their forties.

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That deadline is the force behind innumerable decisions made by women, ranging from when to have a family, how to approach the dating market and how to manage their careers.

Men are far luckier in this respect, for they produce sperm from germline cells in their testes throughout their lives.

But the latest research suggests that, one day, women may be able to put the clock on hold for years -- and if that happens, the social impact will echo just as loudly as the introduction of the contraceptive pill in 1960.

One plank of the "clock" theory is that women are born with a given number of eggs in their ovaries and cannot produce any more during their lifespan.

But, 83 years after it was born, this dogma has been hammered by Harvard Medical School (news - web sites) scientists.

They gave pre-pubertal mice a chemical that kills egg cells and were astonished to find the rodents continued to produce eggs in adulthood, proving an ability to generate fresh eggs to replace damaged ones.

"If these findings hold up in humans, all theories about the ageing of the female reproductive system will have to be revisited," says lead researcher Jonathan Tilly, a Harvard professor of obestrics and reproductive biology.

"We also may need to revisit the mechanisms underlying such environmental effects on fertility as smoking, chemotherapy and radiation. Eventually, this could lead to totally new approaches to combating infertility in cancer patients and others."

In his mice, the new eggs were replaced thanks to stem cells -- the immature master cells that grow, or differentiate, into specialised cells -- in the ovaries.

If the same germline stem cells can be found in women, and a way found to make them grow into the egg precursors called follicles, the menopause could be postponed.

"Germline stem cells in humans might easily have been missed for the same reasons that they escaped detection in mice for so long," says Allan Sprading of the Carnegie Institution in Washington.

He speculates that depletion of these germ c