There is less than a 50/50 chance of it working first time around, even though Michelle is relatively young.

If not, they will have to undergo further IVF treatment.

Charlie's disease affects only 50 children in the UK, and he currently needs blood transfusions every three weeks and painful injections almost daily just to keep him alive.

Even if the new baby is a match, there is only a tiny chance that it will develop Charlie's illness.

Stem cells

The umbilical cord contains a type of primitive cell called a stem cell which could help 'kick start' Charlie's body into producing the red blood cells he needs.

The cells would be infused into him in a similar fashion to a bone marrow transplant.

The Human Fertilisation and Embryology Authority (HFEA), which regulates fertility treatment in the UK, ruled that while it was acceptable to test and select embryos to prevent the birth of a baby with a genetic disease, it was not ethically acceptable to select them in order to help another child.

Julie du Plessis, Education Officer for the campaigning group LIFE, said, "This case has pushed the boundaries of science too far".

"Children should not be created in order to serve the medical needs of older siblings . We are creating an industry where children are made to order, bought and sold."