Surgeons are to implant a woman with an ovary frozen when she was a child so that she can become a mother, in a world first.
The British case involves a woman of 23, who had her ovary removed and frozen at the age of 8.
If treatment succeeds, Moaza Alnatrooshi will be the first woman in the world to become pregnant after having an ovary frozen before the onset of puberty.
A breakthrough would give hope to thousands of other girls who are unable to conceive because their reproductive organs have been damaged by treatment for cancer and other diseases.
Last year doctors in Belgium revealed that they had managed to restore the fertility of a young woman using frozen ovary tissue which had been removed when she was 13. The 28-year-old woman, whose tissue was taken and frozen before she began chemotherapy as a teenager, gave birth to a healthy baby boy in November 2014.
The current case is the first to involve a female patient whose ovaries were taken long before puberty began.
Alnatrooshi had her ovaries removed because she was being treated for beta thalassaemia, an inherited blood disorder, at Great Ormond Street Hospital in London. She had chemotherapy, which damages the ovaries, before a bone marrow transplant.
Alnatrooshi, who is from Dubai but is staying in Britain for her treatment, told the Sunday Times: "My mum did this huge thing for me which is that she froze my ovary and saved it for me until I grew up and used it.
"I want to believe I will be pregnant. I cannot wait for that day. I would like to say to all women that they have got to have hope."