A 28-year-old woman gave birth to a healthy baby girl after an ovarian tissue transplant (search) reversed infertility caused by cancer treatment, doctors in Israel are reporting.

Last year, a Belgian woman gave birth after such an operation, but the claim was controversial because the egg could have come from her remaining ovary, not the transplanted tissue.

The case reported Monday by Dr. Dror Meirow of Sheba Medical Center in Tel Aviv is more convincing because menopause (search) was documented for two years before the transplant. The New England Journal of Medicine reported the case on the Internet and will publish it in its July 21 issue.

Doctors froze ovarian tissue from the woman before she had high doses of drugs for non-Hodgkin's lymphoma. Two years later, lab tests showed she remained infertile. Strips of her frozen tissue were attached to her left ovary and fragments of it were injected into the right one.

Nine months later she had resumed having periods. A single egg was retrieved from the left ovary, fertilized with her husband's sperm in a lab dish, and the pregnancy resulted from the resulting embryo.

"Although we cannot rule out the possibility that this egg was derived from the native ovary, we consider this possibility very unlikely" because of the timing of pregnancy and tests consistently showing the woman had been infertile before that, the doctors write.

At an American Society for Reproductive Medicine (search) last fall, Meirow described experimental techniques to ensure that transplanted tissue did not harbor cancer cells — a theoretical risk that doctors worry may make such transplants unsafe for women.

The society's guidelines say that freezing eggs and ovarian tissue are promising but experimental options that should be offered only to cancer patients through programs that ensure they understand the risks.