Doctors will decide tomorrow whether to carry out an operation this week to separate the newborn conjoined twins Faith and Hope Williams.

Their mother, Laura, became the world’s youngest mother of conjoined twins at just 18. The babies, delivered by Caesarean section on Wednesday, are being cared for at the Great Ormond Street Hospital for Children in London.

Agostino Pierro, Nuffield Professor of Paediatric Surgery at the hospital, said yesterday that the sisters’ hearts had significant congenital abnormalities that could require surgery.

“The current concern is that the two hearts and the joined circulation raise a risk that the children might suddenly deteriorate and need emergency separation surgery,” he said.

Mr Pierro said that the large blood vessels run from one child to the other, and are joined at the liver and intestine. “Although the team would prefer to leave surgery until the children are older and stronger, increasingly we believe that this may be risky.

“A meeting will be held on Tuesday to decide whether to attempt a planned separation this week, but it will be the parents who finally decide.”

Doctors initially warned Mrs Williams and her husband, Aled, 28, that the twins might not survive after a 12-week scan revealed they were joined from their breastbone to the top of their navels. The couple, from Shrewsbury, refused to have a termination.

Mrs Williams yesterday described the moment that she first saw her babies at University College London (UCL) hospital after their delivery. The girls, delivered after 35 weeks’ gestation, had a combined weight of 10lb 8oz. “After I came round from the operation they wheeled me in to see them,” she told The Mail on Sunday. “They had tucked Hope’s arm underneath, and it was Faith’s arm that I could see. I touched her and I took her hand and she was grasping it. They were both blowing little bubbles.

“They were so beautiful, I couldn’t stop looking at them. After everything everyone said, I’m so glad they’ve proved them all wrong.”

An hour after the birth the twins were christened and put in an ambulance to Great Ormond Street, one of the leading European centres for the care of conjoined twins.

Mrs Williams said: “We knew conjoined twinsrarely make it through the first 24 hours, and we could see that one girl was a bit smaller than the other so we called the little one Hope and the bigger one Faith.

“They have all their own limbs and their own hearts. The only thing they share is the liver. As that’s the only major organ that can regenerate, the doctors can split it between the two of them and it will grow back.”

Mrs Williams, who has an 18-month-old daughter, has been discharged from hospital and is staying at Great Ormond Street, where the twins are being treated in intensive care.

Her husband, a dustman originally from Anglesey, North Wales, said: “No words can describe it. I was so excited and happy, and when I heard them screaming, it was like the world had lifted off my shoulders,” he said.

“The first thing I did was tell Laura they were all right, and when I did, a single tear fell down her cheek.”

The couple have said that when the first scan at 12 weeks showed the twins were conjoined, doctors at Royal Shrewsbury Hospital said they would probably not live beyond two weeks. The doctors also cautioned that if Mrs Williams went through with the pregnancy, complications mightleave her unable to have further children.

Mrs Williams spent a month at Birmingham Woman’s Hospital before being transferred to UCL hospital on Monday morning.

A 30-strong medical team from the Elizabeth Garreth Anderson wing of UCL hospital were present when the consultant obstetrician Pat O’Brien performed the Caesarean section.

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