A complex task that can throw up nasty surprises

The team of surgeons operating on Jodie and Mary will have been warned to prepare for nasty surprises. However careful the planning for the operation - and modern techniques using X-rays and scanners make that a lot easier than in the past - surgery on Siamese twins invariably throws up something unexpected.

The team of surgeons operating on Jodie and Mary will have been warned to prepare for nasty surprises. However careful the planning for the operation - and modern techniques using X-rays and scanners make that a lot easier than in the past - surgery on Siamese twins invariably throws up something unexpected.

The operation will have involved severing the blood vessels that supply Mary, the weaker, with oxygen. Her malformed heart and lungs failed shortly after birth and she has been kept alive since by Jodie.

The most difficult moment, emotionally, for the team will have been the expected death of Mary. Lawrence Somers, a surgeon who separated a similar set of twins in Philadelphia in 1979, described it thus: "It was absolutely silent in there when that happened. It was like a major tragedy, even though everybody knew that it would happen."

The delicate task of separating the twins will have been made easier by the fact that only one could possibly survive, so there would have been no need to divide tissue fairly between them.

The twins were joined at the abdomen and had a fused spine as well as sharing a bladder. Jodie has a normal brain, heart, lungs and liver. She has normal legs but her hips were dislocated, causing the legs to lie at right angles to her body. She will have had surgery on her bowel and bladder and orthopaedic surgery to relocate her hips. One of the trickiest parts of the operation will have been the separation of thespines where a false move could leave Jodie paralysed.

Jodie's chances of surviving the surgery have been put at 95 per cent. Doctors believe she will have normal intelligence, be able to walk and bear children and have an average life expectancy.

The surgical team will have prepared for the operation with an extensive series of tests, including X-rays, magnetic resonance scans and arteriography to locate the organs and blood vessels and determine how the twins are joined. They will also have done kidney and liver function tests and ECGs to check the functioning of Jodie's heart.

However, Professor Lewis Spitz, Britain's leading specialist who has cared for 17 sets of Siamese twins at Great Ormond Street hospital, said there was always the danger of the unexpected. "You have got to be prepared for something not disclosed in the investigations. You have to be able to think on your feet." The chances of success are much higher where, as in this case, the operation is planned and not carried out as an emergency.

Professor Spitz said: "They vary enormously in complexity. The surgery can be simpler than some cancer surgery. But it is much more than just the surgery. It is the anaesthesia, the pre-operative investigations, the post-operative care, the intensive care unit - all can affect the outcome."