A woman who became infertile in her teens has given birth to a baby girl after receiving healthy ovary tissue from her identical twin sister.
The Yarber sisters both recovered well from the procedure
The transplant was carried out at St Luke's Hospital in St Louis in April last year.
Soon after the procedure was completed the previously infertile 25-year-old woman started having periods.
Doctors told the New England Journal of Medicine how it might help advance ways to preserve cancer patients' fertility.
It is thought to be the first birth following transplantation of ovarian tissue from one person to another.
Stephanie Yarber went through a very early menopause at the age of 14, but her identical twin sister - Melanie Morgan - did not.
She has had three children and wanted to donate her eggs so her sister could also become a mother.
But this did not work, so she donated some tissue from her healthy ovaries instead.
In a five-hour operation last year at St Luke's Hospital in St Louis, doctors removed the ovary, and separated off the outer tissue that contains the egg-producing follicles.
They then grafted a third of this tissue on to each of Mrs Yarber's ovaries, while the final third was kept back in case the initial transplants did not work.
The risk of organ rejection was minimal because identical twins have the same genes increasing the chances of success.
Dr Sherman Silber and colleagues who carried out the operation said although ovarian transplantation between identical twins would be rare, the technique had great potential for many women.
"The demonstration that ovarian function can be restored and that natural conception and successful pregnancy can be achieved after transplantation of ovarian tissue may have broader implications for young women, such as those who require potentially sterilising treatment for cancer."
Dr Allan Pacey, secretary of the British Fertility Society and senior lecturer at Sheffield University, agreed.
"The success of this procedure may help us to better understand how to help women who want to preserve their fertility prior to potentially sterilising cancer treatment.
"To be able to successfully graft back a piece of a woman's ovary that was frozen before her cancer treatment, would be of great benefit to women who were diagnosed with cancer at an early age."
However, he said: "This kind of transplantation would be very, very rare and is not without risk to either party. For the majority of cases, egg donation would be a much easier and safer option."