One of two conjoined twin girls born to an 18-year-old British woman a week ago died due to lung failure after she was separated from her sister in an emergency operation at London’s Great Ormond Street Hospital, says Professor Agostino Pierro.

The mother, Laura Williams, of Shrewsbury, gave birth to the girls at the hospital on November 26. The twins were joined at the chest and shared a liver but had separate hearts. They underwent the separation operation on Tuesday and one of them, Hope, died in the process, with her parents present.

The head of the surgeons’ team which operated on the girls, Prof. Pierro, said Faith had some trouble breathing but was slowly improving. The team operated on Faith after Hope died, for a total of 11 hours. Faith will need further surgery to close her stomach. She is currently in ICU.

The hospital intended to postpone the surgery until the twins were stronger, but they had to go through after health problems appeared.

Professor Pierro said: ''This was an emergency operation because there was a blockage in their joined intestine which could only be resolved through separation. The technical separation worked well, although it was extremely challenging, and went according to plan.'' Nevertheless, Hope’s lungs failed to support her after the separation, and she soon died.

Pierro went on to express his regret for the Williams’ loss. "The parents are coping extremely well and I am grateful to them for their support," he said.

Some 20 medical staff was involved in the operation, and Professor Pierro said it was one of the most challenging and complex he and his staff had ever faced. The staff at the hospital is considered some of the most experienced in Europe in the separation of conjoined twins.

Mrs. Williams is, or was, the world’s youngest mother of conjoined twins.