"I can get pregnant the natural way - that's something I could never have hoped for a couple of years ago"

" Ovarian tissue transplants have been carried out before - but only between twin sisters with the same genetic make up. "

" In 1990 at the age of 20, Ms Alvaro received extensive treatment for beta-thalassemia, an inherited blood disorder, including chemotherapy and radiotherapy, and a bone marrow transplant from her young sister Sandra. "

" In 2005 Ms Alvaro consulted Professor Jacques Donnez, of the Catholic University of Louvain in Brussels, about the possibility of an ovarian tissue transplant from her sister to give her the chance of becoming pregnant. "

" She rejected the idea of an egg donation from her sister, as she wanted to be "responsible" for maturing the egg in her own body, and did not want her sister to have to take ovary-stimulating drugs. "

" Her sister's cells had mixed with her own, and although they were genetically different, they were able to co-exist successfully together - meaning Teresa would not have to take drugs to stop her sister's ovarian tissue being rejected. "

" Teresa received three small sections of ovarian tissue from her sister in an operation in February 2006. "

" The sisters were discharged from hospital the day after surgery, and after six months Teresa started to menstruate again, indicating ovarian function had been restored. Her menstrual cycles have continued ever since. "

" A year after the transplant, the doctors retrieved two mature eggs from her ovary and fertilised them with her husband's sperm. "

" One of the resulting embryos developed to the two-cell stage and the other to the three-cell stage, but then both ceased to develop further, and so the embryos were not transferred to her uterus. "

"Woman to woman transplants like this may become common if suitable donors are willing to come forward"

" Professor Donnez said: "We do not know why the embryos ceased to develop,
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