AN AMERICAN woman who was sterilised by cancer treatment will give birth this weekend after an operation that could change the foundations of reproductive biology.

The case of Ann Dauer has raised the possibility that human ovaries can be “reseeded” with eggs to restore fertility after the menopause.

If doctors’ suspicions about the causes of her pregnancy are confirmed, it would indicate that women are not born with all the eggs they will ever have, as is generally thought, but can replenish their ovaries from stem cells throughout their lives. This would promise new methods to protect the fertility of cancer patients, and could allow healthy women to defy the menopause.

Mrs Dauer, 33, from Canton, Ohio, was left infertile three years ago by chemotherapy for Hodgkin’s lymphoma, but had one of her ovaries removed and frozen before treatment in an attempt to preserve her ability to have children. She conceived naturally after slices of the frozen ovarian tissue were thawed and implanted last year, restarting her menstrual cycle.

Two other women, one in Belgium and one in Israel, have already given birth after similar procedures, but Mrs Dauer’s case is unique in a way that has astounded scientists. While the other patients had tissue reimplanted in the ovary’s normal position, her graft was placed under the skin of her abdomen. The idea was then to remove eggs using a needle and fertilise them by IVF.

The position of Mrs Dauer’s graft should not have allowed natural conception as there was no route for eggs to travel to the Fallopian tubes and the womb. But when her doctors examined her before attempting IVF, they were amazed to find her pregnant.

“I did the ultrasound and almost fell off my chair,” Kutluk Oktay, of the Weill Cornell Medical Centre, in New York, said. “That pregnancy unfortunately miscarried, but when we examined Ann the next month she was pregnant again. Her treatment was almost guaranteed to make her menopausal. This really shouldn’t have happened.”

A handful of patients recover their fertility naturally after chemotherapy, though this is so rare after the type of treatment Mrs Dauer received that her chances were estimated at one in five million.

It is also possible that hormones from the graft have helped her remaining ovary to recover, though scientists think this unlikely as several dozen patients have received similar subcutaneous implants without becoming pregnant.

A third explanation is the most outlandish, but the most exciting. Research by Jonathan Tilly, of Massachusetts General Hospital, has suggested that in mouse ovaries, the stock of egg follicles is constantly replenished by specialised stem cells known as germ cells. Though this work is controversial, it is conceivable that something similar has happened to Mrs Dauer.

“This is a wild explanation, but there is animal work that shows germ stem cells may travel to the ovaries through the bloodstream,” Dr Oktay said. “It’s just possible that the transplanted ovary supplied something that the damaged ovary didn’t have, and that germ cells have moved through the blood to reseed it and allow it to start working again.

“Each of the three possibilities is very unlikely, and there’s no way now for us to determine which one it is in this patient. But there are laboratory studies we can do to determine whether reseeding is possible in human tissue, and that has to be the next step.”

Dr Oktay accepts that it is impossible to prove whether the grafted ovary has revived the other. Another of his patients, however, has also shown egg follicle development in her menopausal ovary after having similar treatment to Mrs Dauer, though she has not yet conceived.

If reseeding is possible in humans, it could allow doctors to beat the menopause by storing ovarian tissue and reimplanting it under the skin in a very simple and minimally invasive operation.

Professor Bill Ledger, of the University of Sheffield, said that while spontaneous recovery was the most likely explanation, the stem-cell theory was fascinating and credible.

“It is unusual, but there have been reports of ovarian recovery even many years after a woman appears to have become menopausal,” he said.

“It’s unlikely that hormones are responsible, but the third option is most intriguing. It has a certain biological plausibility if the mouse work is accurate.

“This is a really challenging concept, as it goes against everything we have always believed about how the body works. If one ovary could track the other and repopulate it with follicles, that would be a very nice idea.”

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