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Clarification Appended: March 14, 2009

For Stephanie Yarber, who received a diagnosis of premature ovarian failure at age 14, conceiving children the old-fashioned way was a life's wish. In 2003, after several unsuccessful — and costly — courses of in vitro fertilization (IVF) using her identical-twin sister's donated eggs, Yarber began looking into other options. There was adoption, of course. But there was also a riskier experimental alternative: ovarian transplantation.

In her research, Yarber came across a surgeon and fertility specialist in Missouri, Dr. Sherman Silber of the Infertility Center of St. Louis, who in the late 1970s had performed the first successful testicular transplant between male identical twins, allowing the once infertile brother to father five children. Yarber wondered if the same doctor could do a similar procedure between her and her sister. Yarber's sister, who had three daughters and didn't plan to have any more children, eagerly agreed to help. "She wouldn't have said no," Yarber says. "I knew that." (See the top 10 medical breakthroughs of the past year.)

Silber remembers the day he first spoke to Yarber. Her enthusiasm was contagious. But despite his vast experience with microsurgery and his success with male patients (he had also performed the world's first vasectomy reversal), Silber knew that all previous ovarian transplants in the U.S. had failed, as had those performed abroad. Still, he thought, in theory the procedure was possible. Yarber's surgery was scheduled for April 2004.

Yarber's microsurgical procedure involved the transplantation from her sister to her of a thin strip of cortical tissue — the part of the ovary that produces eggs. (The leftover strips of egg-producing tissue from the harvested ovary were frozen and stored for future use.) Within months, Yarber began menstruating. In September 2004, just five months after the transplant, she was pregnant. Five years and another tissue transplant later, Yarber has two daughters, ages 3½ years and 10 months, and is trying for a third child. Owing in large part to Yarber's willingness to talk about her experience, Silber has since performed the same procedure for eight other sets of identical twins. "There are lots of women who are in our position who are not able to have children and who are looking for something," says Yarber. "If we didn't speak about it, there wouldn't have been so many other twins able to do it."

The battle to preserve and prolong women's fertility has become increasingly visible of late. While advances in techniques like cryopreservation (the freezing and storing of eggs and embryos, for example, and now also ovarian tissue for transplants) have increased many women's chances of pregnancy, IVF is still a time-consuming and expensive process — and one that holds no guarantees. Success rates with IVF parallel fertility rates in the general population, dramatically declining with age. After 40, success rates drop to as low as 23%, and after age 43, Silber says, pregnancy is very rare.

But other fertility treatments — including experimental procedures such as harvesting immature eggs and maturing them in vitro for IVF, and the transplantation of ovarian tissue or entire intact ovaries — have gained ground in the past five years, especially for women with premature infertility or infertility resulting from cancer therapy. An article published in the Feb. 26 issue of the New England Journal of Medicine urges oncologists to consider fertility preservation, including the use of experimental techniques, more routinely with their patients, since as many as 90% of women who undergo full-body radiation become infertile. But even as fertility specialists offer hope for many women who believed they would never bear their own children, ethicists warn that doctors must tread carefully in developing the technology.

Silber, prompted by success with cortical-tissue transplants, decided to try transplanting a whole ovary. He performed the first successful such transplant between a set of 38-year-old identical twins in January 2007. A few months after surgery, the infertile twin got her period for the first time in more than two decades. Less than a year later, she was pregnant. Last November, she gave birth to a healthy baby girl.

One month after performing the whole-ovary transplant, Silber tried the same procedure on a set of nonidentical twins for the first time. The recipient of the ovary, a San Francisco woman named Joy Lagos, had become infertile after cancer treatment. But the hope was that because Lagos had received a bone-marrow transplant from her older sister as part of that treatment — which transformed Lagos' immune system into a chimera, or hybrid, of her sister's and her own cells — her combination immune system would stand a far better chance of accepting her sister's ovary without the need for long-term immunosuppressant drugs.

The procedure went off without a hitch. But several months later, Lagos' hormones began reverting to menopausal levels. The ovary failed. In October 2007 she tried again, with a cortical-tissue transplant from her sister, harvested during the earlier procedure. Six months later, Lagos got her period for the first time in years. "This means that the ovary is working and we can start trying to get pregnant for real!" she wrote ecstatically on the blog she shares with her husband. But by summer, Lagos learned that the second transplant had also failed. Silber concluded it was most likely an organ rejection.

"I view this as an error in judgment," says Silber. "We all thought we didn't have to immunosuppress her." Yet with the use of immunosuppressant drugs, he says, the technique could work between sisters or even strangers. "We know that's a safe thing to do," Silber says, citing the many published cases of babies born to women on long-term immunosuppressants. And because ovaries are not vital organs, he says, the immunosuppressant regimen for ovary-transplant patients would be much more modest than average. "If it doesn't work, we're not going to take a chance with their life as we would with a kidney or a liver," he says.

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But using immunosuppressant therapy at all for nonlifesaving transplants lies in murky ethical territory, says Dr. Roger Gosden, director of reproductive-biology research at Cornell's Center for Reproductive Medicine and Infertility. Gosden, who did early research in ovarian transplantation in sheep and has co-authored several papers with Silber, says it's difficult to justify such drastic measures when there are so many other avenues to motherhood — adoption, surrogacy, egg donation. What's more, the prospect of a lifetime of drug therapy and its impact on the patient need to be heavily weighed, he says. "I suppose you could say, 'She could have the transplant, try to get pregnant and later have it removed, and then stop the immunosuppression.' " But that course of treatment may stretch the boundaries of what is medically ethical and reasonable for the patient. "It becomes very tricky," he says.

Tricky and possibly unrealistic, says Dr. Mitchell Rosen, director of the Fertility Preservation Center and Reproductive Laboratories at the University of California, San Francisco. "I don't think it would be used as a mainstream form of fertility treatment," he says. "I don't think it's going to replace IVF." Though he acknowledges the powerful desire to conceive the old-fashioned way, he points out that compared with the transplant process — finding an organ donor, enduring a long surgery and facing the possibility of a lifetime of drug therapy — IVF offers a simpler, more logical route. (Read "The Year in Medicine 2008: From A to Z.")

Still, fertility specialists agree that ovarian transplantation may be vital for patients suffering from life-threatening diseases. "It's a no-brainer that we should offer this to cancer patients," says Silber.

Amy Tucker, now a 31-year-old registered nurse, received a Hodgkin's disease diagnosis a little more than a decade ago. She underwent six months of initial treatment, after which the cancer recurred. Tucker was then scheduled for a bone-marrow transplant, full-body radiation and additional chemotherapy. But a couple of days before her bone-marrow transplant was to take place, a nurse practitioner happened to mention a lecture she had heard given by a local fertility specialist, Dr. Silber. Until then, Tucker had not once considered her fertility or, for that matter, anything else but the cancer treatment at hand.

Tucker subsequently had her right ovary removed and the tissue preserved. In January, a full decade later, she had her own tissue transplanted back into her body. Now, she hopes, she'll be able to bear her own children. "I haven't had a period for 10 years," she says. "But now, oh my God, I might actually be able to get pregnant."

One reason specialists urge moving toward whole-organ preservation for cancer patients is that it can be done so quickly. Tucker was able to have her ovary removed right away — unlike harvesting eggs, which can take weeks — and that meant she could begin her cancer treatment without delay. It would take another decade for Tucker to start thinking about children or reimplanting the ovarian tissue. "Basically, Dr. Silber had said, 'It doesn't matter when you put it back in. It's the ovary of a 20-year-old,' " Tucker says.

That's what makes the technique potentially appealing for other women — healthy women who simply want to delay pregnancy for lifestyle purposes. "For those who want to have children, they will often say that it is the supreme experience in their life. To deny that, or to provide obstacles when technology allows it, would be a matter of deep concern," says Gosden. Though he believes that physicians should seriously consider the ethical implications of using ovary transplants liberally to extend fertility, he says much of the debate will be decided by the would-be mothers themselves.

The primary concern, says Rosen, is the tragedy of a false promise. "You don't want to take a population and promise them something — tell them it's O.K. to wait until you're 40," he says. At 40, the transplant may not work.

Silber says without hesitation that he would help all women who wish to preserve their fertility this way — as long as patients were fully aware of the potential risks of ovary removal, which include early menopause. In fact, Silber is currently awaiting Institutional Review Board approval to perform ovary-tissue transplants for seven nonidentical twin pairs who have asked for it. (The potential transplant patients are Orthodox Jews, who for religious reasons are prohibited from using donor eggs.) He estimates that he should be able to perform the surgeries within a matter of months. "I know there will be people who have big ethical debates about it," he says, but in many ways, this seems like a logical progression of science. "Women are able to put off childbearing because of these enhanced opportunities in society and often don't seriously think about having kids until they're 35 or 40. By then, there's a 50% chance that they're infertile," he says. "Normally, we worry that science is getting way ahead of society," Silber adds. "This is exactly the opposite of that."

The original version of this article neglected to mention the context in which Dr. Silber hopes to perform ovary-tissue transplants for seven nonidentical twin pairs: to restore fertility in women whose religion prohibits them from using donor eggs. The article has been modified to include that information.

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• Tiffany Sharples
• An experimental technique may help preserve fertility in cancer patients and other women struck with premature infertility. It may even be used for healthy women who just want to wait