LONDON (AP) -- When Stinne Holm Bergholdt of Denmark was diagnosed with bone cancer at age 27, she was afraid she wouldn't be able to have children.

So she asked her doctors if they could remove an ovary before her treatment and transplant it back afterward to preserve her fertility.

More than six years later, Bergholdt and her husband now have two daughters, making her the first woman in the world to give birth twice after an ovary transplant.

Details of her case were being published online Thursday in the journal, Human Reproduction.

"It's hard to believe it's really true," said Bergholdt, of Odense, Denmark. "It's like a dream that I never would have thought possible a few years ago."

On the day before she started chemotherapy, doctors took 13 strips of ovarian tissue from Bergholdt's right ovary and froze them. After eight months of cancer treatment and another year of recovery, doctors reimplanted seven of the strips, or about 20 percent of an entire ovary.

Bergholdt's ovary began working again after a few months, and she then had in-vitro fertilization to become pregnant. Nearly a year later, she gave birth to daughter Aviaja, now 3. Bergholdt's treatment was paid for by the Danish health system.

When Bergholdt and her husband decided they wanted a second child, they went back to the fertility clinic, but it turned out that she was already pregnant. About a year ago, she gave birth to another daughter, Lucca.

"We were really surprised that she had done it herself," said Dr. Claus Yding Andersen, one of Bergoldt's doctors at University Hospital of Copenhagen. "We did not expect the ovary transplant to still be working after four years."

The transplant is working so well that Bergholdt is currently using birth control to avoid becoming pregnant again.

Eight children have been born worldwide to women who have had ovary transplants but no other woman has had more than one pregnancy after having a transplant.

The technique has been mostly used for cancer patients, but could become more widespread as the technology is refined, Andersen said.

"It shows we can stop the clock by freezing the ovaries," he said.

Women who want to delay having children might also be interested in the procedure although that could raise some ethical issues, he added.

Others thought an ovary transplant was much too invasive to become more widespread.

"To suggest that a healthy woman would have two operations (to remove and reimplant the ovary) for the sake of social convenience, to have children later, is ludicrous," said Allan Pacey, a fertility expert at the University of Sheffield, who was not linked to the research. "It's far easier to just freeze your eggs."

Still, Pacey said Bergholdt's case proved that ovary transplants were a viable way to preserve women's fertility and should reassure cancer patients they won't automatically be left sterile.

For Bergholdt, the transplant was a blessing.

"It was very hard to believe after everything I'd been through I could actually have children," she said. "Now that we know this technique works, it should be available to every woman who goes through cancer treatment."

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