London ? The first baby conceived after an ovarian tissue transplant was born Thursday in Belgium in a procedure that could one day allow women to delay motherhood beyond menopause.

The birth, announced by The Lancet medical journal, which is to publish the results of the procedure today, marks the first time fertility has been restored to a woman after doctors cut out and froze some of her ovarian tissue and transplanted it back into her body years later.

One pioneer in the field was cautious about the report, saying there is a small chance the baby came from the existing ovaries rather than the transplanted tissue. However, he said the doctors from Catholic University in Louvain, Belgium, made a strong case that the birth resulted from the transplant.

The technique has worked in monkeys, but until now has not resulted in a successful pregnancy in humans.

The operation — long hoped for by fertility specialists — has been developed over the last few years to help women whose ovaries are damaged or destroyed by cancer treatment or other major surgery.

In this case, Dr. Jaques Donnez of the Catholic University, cut ovarian tissue out of a woman who was about to undergo chemotherapy and radiation for Hodgkin’s lymphoma in 1997.

Five years after she was cleared of cancer, the tissue was grafted back onto her fallopian tubes. The woman, 32, became pregnant naturally and gave birth Thursday in Brussels to a healthy 8-pound 3-ounce girl.

“It cannot be proved with 100 percent certainty (that the pregnancy came from the graft) because ovulation from the transplant was calculated from temperature, but was not confirmed,” said Dr. Kutluk Oktay, an expert who was not involved with the operation but has conducted much of the key research in the field.

Even though the woman’s remaining ovarian tissue stopped working after the cancer treatment, it recovered and she ovulated three years later, which indicates it’s possible that the native ovaries could have ovulated again to produce the baby, Oktay said.