Charlotte Mariethoz, from Leicester, has a rare blood condition called diamond blackfan anaemia and her only hope of survival is by a stem cell transplant from a genetically matched donor.
So doctors now plan to create embryos through IVF treatment on her parents and those will be tested when they are a few days old to find a perfect genetic match. If there is a perfect match then the embryo will be implanted in Mrs Mariethoz's womb. After the baby is born, the doctors will remove the stem cells from the umbilical cord and transplanted into Charlotte.
Diamond blackfan anaemia is a condition that affects only 100 children in the UK but sufferers usually die by 30. The condition is not genetic and the embryo tests will ensure the second baby does not have the same condition.
Anti-abortion groups have always opposed to preimplantation genetic diagnosis, as they claim that the procedure would be abused, allowing designer babies to be created on the basis of their eye colour or sex. They are also concerned about the pressure on any "saviour sibling" if the treatment does not save their elder brother or sister.
Last year the governmant ruled that the technique could be authorised and a small number of licences have been issued. Julie and Joe Fletcher were the first UK couple to have a "saviour sibling" last July. Their daughter Jodie was a perfect match for her three-year-old brother Joshua, who has diamond blackfan anaemia.