British conjoined twins separated

The operation took four hours

Twins joined at the chest have been successfully separated in a four hour operation at Great Ormond Street Hospital in London.

The twin girls are said to be doing well in the hours immediately after the procedure.

The parents, from the UK, have asked for no personal details to be made public for the time being.

While it is early days, a good outcome for both children is likely

Professor Lewis Spitz, Great Ormond Street Hospital

The twins were joined at the chest and abdomen, and shared a single liver, which had to be split between them.

The operation, planned since Christmas, involved four surgeons, four anaesthetists, and dozens of other hospital staff spread over two operating theatres.

Four out of five

The survival rate for pre-planned operations to separate twins is 80% at Great Ormond Street.

Mortality for conjoined twins generally is much higher, as many cases are deemed inoperable, and others have to be carried out on an emergency basis, which is far harder.

We're looking forward to taking the girls home

Statement from parents of twins

The lead surgeon involved in the case, Professor Lewis Spitz, said: "While it is early days, a good outcome for both children is likely."

A statement released by the mother and father said: "We're grateful for the care that Great Ormond Street has given our children - we'd also like to thank the hospital where the twins were born, where we had good care.

"We're looking forward to taking the girls home."

Conjoined twins are created when a single fertilised egg splits, but separation of the two identical twins is incomplete.

They are extremely rare - perhaps one in every 200,000 live births.

The survival rate is entirely dependent on where the twins are joined, and how many organs they share.

In this case, a shared liver meant it was slightly easier to separate the twins with the prospect of both surviving.

If a heart were shared, then one of the twins would certainly die, and the operation would be far more complex.

Professor Spitz is one of the leading surgeons in the world at these operations.