Doctors will decide tomorrow whether to separate the newborn conjoined twins Faith and Hope Williams this week.
The twins were delivered by caesarean section on Wednesday and are being treated at Great Ormond Street Hospital for Children. Their mother, Laura Williams, 18, made history as the youngest woman to give birth to conjoined twins.
A 12-week scan showed that the twins were joined from their breast bone to their navels and doctors warned her and her husband, Aled, that the babies might not survive.
The couple, from Shrewsbury, Shropshire, refused to terminate the pregnancy. Mrs Williams said: "From the first time I felt them kick, I thought they were going to be OK. And they're still here. They're little fighters. They have all their own limbs and their own hearts. The only thing they share is the liver and 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."
The Nuffield Professor of paediatric surgery at the hospital, Agos tino Pierro, said abormalities with the babies' hearts meant they could require an emergency separation.
"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 decide."