The twin girls, born last Thursday at the Queen Mother's Maternity Hospital, Glasgow, are joined at the chest and the abdomen and have severe liver, kidney and bowel abnormalities.
The shared heart effectively rules out any chance of both twins surviving an operation to separate them. The parents, who have not been identified, have said they would only agree to separation if there was a good chance for each baby to enjoy a reasonable quality of life.
The babies, born four weeks early by Caesarean section, weighed 11lb and are being ventilated and fed intravenously in the hospital's intensive- care unit. Both have been baptised and their mother was able to hold them the day after delivery.
A detailed investigation of their conjoined state has not been possible because of their poor condition, Dr Barbara Holland, a consultant paediatrician, said yesterday. She said they may survive days or even weeks, but their outlook was "very poor".
"They have very severe illnesses and it's doubtful they will survive very long. They have abnormalities of several of their organs," Dr Holland said.
The mother of the twins, a woman in her thirties from central Scotland, who has other children, was unaware that she was having two babies until the day before their birth.
She had undergone an ultrasound scan at her local hospital because doctors thought she was large for her stage of pregnancy. When conjoined twins were identified, she was referred to Glasgow for confirmation and doctors decided to deliver the babies immediately.
A spokesman at the hospital said yesterday that the woman had had a routine scan at 8-12 weeks of pregnancy and no problems were identified. It appears that another routine scan at 16-20 weeks did not take place - some women decline this - and apart from her size, there were no indications that the pregnancy was abnormal.
Dr Gavin Hanretty, who with Dr Allan Cameron delivered the children, said the delivery was well planned and "pretty straightforward in the circumstances". It took about 40 minutes. He said the parents were very anxious but were receiving support from hospital staff and their own family.
"They have been kept fully informed and have had a lot of contact with their children ... [the mother] appears to be remarkably well under the circumstances," he said.
Shared bodies, different lives
Conjoined (Siamese) twins are identical twins who have failed to separate completely from a single fertilised egg.
In Britain in the 12th century, Mary and Elisa Chulkhurst from Kent, joined at the hip and shoulder, are reputed to have lived until the age of 34.
The first-recorded Siamese twins in modern times - and the best known - were Chang and Eng born in Thailand (formerly Siam) in 1811.
Until their death in 1993 at the age of 43, Yvonne and Yvette McCarther, from Los Angeles, were the world's longest surviving Siamese twins. Joined at the head and sharing the same circulation, they toured in a travelling freak show before training as children's nurses in their 30s.
Chloe and Nicole Astbury were the most recent British Siamese twins, born on 14 September last year at St Mary's Hospital, Manchester.
They were joined from the breast bone to the navel and underwent an operation to separate their bowels in the first few weeks of life. Complete separation was planned for sometime in their first year, but the girls died from a bowel disease.Reuse content