A woman has given birth to two children after her fertility was restored using transplants of ovarian tissue, the first time the complex treatment has produced two babies from separate pregnancies.

Claus Yding Andersen, the Danish doctor who treated the woman, said the case showed how this method of storing ovarian tissue was a valid way of preserving fertility 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, Danish woman 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. She then conceived naturally and gave birth to another girl in September 2008.

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.

Gillian Lockwood, medical director of Midland Fertility Services in central England and Pete Braude, head of women's health at King's College London, both said the key to the success of this kind of treatment was the woman's age.

'The fact that it's possible to get many more eggs from frozen strips of ovarian cortex ... means that it may well be a better option for young cancer patients,' Lockwood told Reuters.

Braude said the fact that Bergholdt was 27 when her treatment began had boosted her chances.

'It worked because there was a large store of eggs, and as you get older that store goes down,' he said. 'If she had been 35 or 36, the likelihood of this succeeding would have been much less.'

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 succeeded but, as expected, also caused a menopause. In 2005, after six strips of ovarian tissue were transplanted onto what remained of her right ovary, it began to function again.

In January 2008 she returned to Andersen's clinic for more fertility treatment to try to conceive again. But a test showed she was already pregnant with her second child.

'This showed that the original transplanted ovarian strips had continued to work for more than four years,' 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, 32, said she had 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,' she said. – Reuters