Faith Williams, the conjoined twin who was separated from her twin at the beginning of December, died on Christmas Day. Her sister, Hope, had died during the operation to separate them.

The pair were born on November 26, joined at the chest, and doctors had warned their parents that the chances of survival were small.

Faith survived three major operations during her four-week life, but finally succumbed at Great Ormond Street Hospital for Children.

Faith, who was described as “very sick”, had been given only a 50 per cent chance of survival after undergoing dangerous surgery on December 2 to separate her from her twin sister.

Hope, the weaker of the two babies, died shortly after the 11-hour separation surgery because her lungs were too small to support her breathing.

The babies' parents, Laura and Aled Williams, were at Faith's bedside when she died. She had lived for just 29 days.

Mrs Williams, 18, became the youngest mother of conjoined twins in Britain when the babies were delivered by Caesarean section after 35 weeks' gestation. They had a combined weight of 10lb 8oz. The couple, from Shrewsbury, had refused to have a termination despite doctors at their local hospital saying that their babies would probably not live beyond two weeks.

Agostino Pierro, the surgeon who led a 20-strong team that separated and treated the babies at Great Ormond Street Hospital, London, said yesterday: “We can confirm that Faith Williams died in the afternoon of Christmas Day.

“This is very sad news and our sincere condolences to Mr and Mrs Williams on their tragic loss. The family will want peace and privacy at this difficult time.

“While this is a sad outcome, it is not an unexpected one,” he added.

Faith and Hope were born joined from the breastbone to the top of the navel and had a shared liver but separate hearts.

Although the operation to separate the babies was a technical success, it was impossible to tell how they would fare after surgery.

Mr and Mrs Williams, who have a strong religious faith, were said to have accepted that the outcome of the surgery would never be certain.

In the weeks since the operation, Faith, the bigger of the two girls, was continuously on the critical list and had two further operations — to correct a heart defect to improve her circulation and, later, surgery to close her chest, which had been left open after the separation.

“We were always clear that Faith was very sick,” Professor Pierro said. “She required the full range of skills of our intensive care staff, and underwent a number of further procedures. However, she succumbed to the complexities of her condition.”

Doctors had hoped to separate the girls when they were older, but the surgery was brought forward after a blockage developed in their joined intestine.

Experience at Great Ormond Street shows that where the separation is performed as an emergency such as this, three out of four babies will die. When the operation is planned, survival rates improve, with eight out of ten babies leaving hospital alive.

Great Ormond Street is the most experienced centre in Europe for separating conjoined twins, an intricate procedure heavily dependent on which vital organs the infants share. The critical period after surgery lasts three to four days, but complications can be fatal. There are some cases where the procedure would mean sacrificing one twin's life to save the other, but none of these has been carried out at the London children's hospital.

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