The death of a child in any circumstances is a tragedy, yet the odds were against either Faith or Hope Williams, the conjoined twins, surviving after their separation.

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

The condition of Faith, who survived an operation to separate her from her sister, Hope, when they were four days old, has shown no improvement since she was put on a ventilator at Great Ormond Street Hospital.

Problems with Faith’s heart and circulatory system caused doctors the greatest anxiety, and she was given only a 50-50 chance of survival.

Faith and Hope were born on November 26 and were joined from the breastbone to the navel. They had separate hearts and lungs but shared a circulatory system, intestine and liver.

Their condition presented an immense challenge to the specialists at Great Ormond Street Hospital, London, who described the operation to separate them as one of the most complex they had faced.

It took a team of 20 doctors, nurses and theatre staff 11 hours to complete the surgery.

But Hope, the weaker twin, died when her underdeveloped lungs proved too small to support her breathing. In the weeks since, her sister 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.

Her parents, Aled and Laura Williams, have a strong religious faith and they accepted that the outcome of the surgery would never be certain.

Mrs Williams, 18, made history by becoming the youngest woman to give birth to conjoined twins. She rejected the offer of a termination when she was told during a routine antenatal scan that the twins were conjoined.

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 10 babies leaving hospital alive.

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