The American team of surgeons told a press conference it had gone as hoped but warned Mohamed and Ahmed Ibrahim were not out of danger yet. They will be kept in a drug-induced coma for a few days to reduce brain swelling, and face years of reconstructive surgery on the areas where their skulls had fused together.

Egyptian and Middle East media have been closely following progress of the operation ? the first such procedure since the death of twin Iranian women during surgery in July. ?Things have gone according to surgical plans,? said Dr Jim Thomas, chief of critical care at the Children?s Medical Center in Dallas, Texas. ?There have been no surprises, and none of the potential complications that surgeons prepared for have occurred.?

Year-long tests

The World Craniofacial Foundation paid for the boys to come to the Children?s Medical Center in Dallas when they were one-year-olds. The twins have separate brains but share a complicated web of blood vessels and circulatory systems that feed the blood to the brain.

Doctors spent a year assessing the chances of successfully separating them. They carried out tests on the boys and visited the team who operated on Guatemalan twins last year. ?Armed with that, plus some very detailed planning, we felt more comfortable proceeding,? said neurosurgeon Dr Kenneth Shapiro, who led the surgical team.

The five neurosurgeons completed the most difficult and dangerous part of the operation to physically separate their blood vessels on Sunday morning ? around 26 hours after the twins entered the surgery room.

Good news

A team of cranial and facial surgeons were then brought in to repair the damage to their skulls, using tissue from their thighs that had been expanded using balloon-like devices months before surgery. The entire operation took 34 hours and a team of 40 doctors, nurses and other staff.

News of the separation overwhelmed the boys? parents, whose devout faith was said to have kept them going through the ordeal. ?When somebody came up and said ?We have two boys?, the father Ibrahim jumped to my neck and he hugged me and he fainted,? said the twins? Egyptian doctor Nasser Abdelal.

?He told me that he never dreamed of such a moment?. The boys? relatives and friends in their home town of al-Homr, near the southern Egyptian city of Qus, were praying for a successful outcome.

?If this is true then this is very good news,? the twins? uncle Nasser Mohammed Ibrahim said upon hearing of the separation.

The family decided to go ahead with the operation knowing there was a risk of brain damage or death to one or both of the twins.

But they said it was the only chance the boys had of a normal life. Conjoined at the crown of the head since birth, the boys had trouble closing their eyes, moving their necks and swallowing.

They could not stand on their own because of the way they were joined, and would have faced certain and progressive loss of functions had they remained as they were.

However, they still face years of reconstructive work to repair the top of their heads that will not have bone underneath.

This is the first operation to separate twins conjoined at the head since the deaths of Laleh and Ladan Bijani in July.

The 29-year-old Iranian women died within 90 minutes of each other from massive blood loss during the separation surgery in Singapore.

However, doctors hope that Ahmed and Mohamed?s young bones and tissue will be able to cope with the strain of the operation and recovery.

Corinne Podger

Medical history

• Born by Caesarean section in Qus, Egypt, 2 June 2001

• Arrived in Dallas in June 2002

• Tissue expanders inserted under skin in April 2003 to prepare for reconstruction

• The twins are now in a critical but stable condition Concerns include the risk of infection and how the wounds will heal

Difficult decision

Ethics of separating twins

What are the ethical difficulties facing those who have to decide whether to operate in the case of conjoined twins? The family and doctors of two-year-old Egyptian conjoined twins Ahmed and Mohammed Ibrahim faced a terrible dilemma when deciding whether to go ahead with the operation. They knew that such an operation would put the boys at considerable risk of either one or both dying or becoming brain damaged.

However, they also knew that if the boys were not separated their condition would only deteriorate. But the decision to separate Ahmed and Mohamed was very different to that facing other conjoined twins ? such as Iranian sisters Ladan and Laleh Bijani, who died during separation surgery in July.

The two cases cover some of the human rights, ethical and medical considerations facing parents and doctors in such situations.

Ahmed and Mohammed are only two-years-old ? too young to actively choose a life apart. While their surgery may still leave them permanently brain damaged, their health was expected to deteriorate as they got older if they remained conjoined. By contrast, Ladan and Laleh Bijani were 29. Although they were healthy adults, they accepted the risk of death in their quest to lead separate lives. Religious questions can also come into play.

In 2000, the Roman Catholic parents of Gracie and Rosie Attard came to Britain from Malta for the girls? birth, but refused separation. A High Court decision allowed doctors to proceed with the separation, which led to Rosie?s death. Michaelangelo and Rina Attard argued at the time it was wrong for the courts to "play God".

After the operation they said they were relieved the judges stopped them from letting nature take its course, condemning both girls to death. "The decision was taken out of our hands in the end but we are happy that the decision to separate was taken by the judges," said Mr Attard to a newspaper after the operation. Doctors who cared for the Bijani sisters say there can be no routine guidelines for conjoined twins; every case is different.

conjoined twins

A poor survival rate

Siamese, or conjoined twins are extremely rare, occurring in as few as one in every 200,000 births. The twins originate from a single fertilised egg, so they are always identical and of the same sex. The developing embryo starts to split into identical twins within the first two weeks after conception. However, the process stops before it is complete, leaving a partially separated egg which develops into a conjoined foetus. The birth of two connected babies can be extremely traumatic and approximately 40-60 % of these births are delivered stillborn with 35 % surviving just one day. The overall survival rate of conjoined twins is somewhere between 5 % and 25 %. Historical records over the past 500 years detail about 600 surviving sets of conjoined twins with more than 70 % of those surviving pairs resulting in female twins.

If they have separate sets of organs, chances for surgery and survival are greater than if they share the same organs.

Conjoined twins are generally classified three ways: l 73 % are connected at mid torso (at the chest wall or upper abdomen) l 23 % at lower torso (sharing hips, legs or genitalia) l 4% at upper torso (connected at the head)

Over the years, survival rates have improved as a result of more accurate imaging studies and better anaesthetic and operative techniques. The term siamese twins was coined as a reference to Eng and Chang Bunker, who achieved international fame following their birth in what was then Siam in 1811.

They were exhibited in circus side shows around the world before settling in the United States and marrying two sisters. They lived 63 years, with Chang fathering 12 children and Eng 10. In the UK an annual celebration was held for centuries to commemorate 12th century siamese twins Mary and Eliza Chalkhurst, wealthy sisters who bequeathed a fortune to the church.