Claus Yding Andersen, the Danish doctor who treated the woman, said the case showed how this method of storing ovarian tissue was a valid method of fertility preservation and should encourage the technique to be used more in girls and young women facing treatment that may damage their ovaries.

This is the first time in the world that a woman has had two children from separate pregnancies as a result of transplanting frozen and thawed ovarian tissue, said Andersen, who reported the case in the Human Reproduction medical journal.

Andersen's patient, a Danish woman called Stinne Holm Bergholdt, had ovarian tissue removed and frozen during treatment for cancer, and then restored once she was cured.

She gave birth to a girl in February 2007 after receiving fertility treatment. But then, in 2008, she discovered she had conceived a second child naturally and gave birth to another girl in September that year.

Nine children have been born worldwide as a result of transplanting frozen and thawed ovarian tissue. Three (including Bergholdt's two) were born in Denmark after treatment carried out by Andersen, who is Professor of Human Reproductive Physiology at the University Hospital of Copenhagen.

It is interesting to note that nearly all of the nine pregnancies have occurred in Europe, he said in a statement. Europe is in the absolute forefront with this technology.

POWERFUL TECHNIQUE

Bergholdt, from Odense, was diagnosed with Ewing's sarcoma when she was 27 in 2004. Before she began chemotherapy, part of her right ovary was removed and frozen.

Her cancer treatment was successful but, as expected, the drugs caused a menopause. In 2005 six strips of ovarian tissue were transplanted on to what remained of her right ovary. Her ovary began to function again and, after mild ovarian stimulation, she became pregnant and had her first daughter.

In January 2008 she returned to Andersen's clinic for more fertility treatment so she could try to conceive again. But a test showed she was already pregnant naturally, and in September she gave birth to another girl.

This showed that the original transplanted ovarian strips had continued to work for more than four years and that Mrs Bergholdt still has the capacity to conceive and give birth to healthy children, Andersen said. It is an amazing fact that these ovarian strips have been working for so long and it provides information on how powerful this technique can be.

Bergholdt, who is now 32, said she is still having natural menstrual cycles but she and her husband have not decided whether to have more children.

The girls are still so small and need a lot of attention, but maybe in a couple of years we might think about it again.

Medicine