Foetuses which suffer from a life-threatening condition can be operated on in the womb and go on to live a normal life, according to the BBC's Tomorrow's World.

The BBC's Craig Doyle on health risks to foetuses

The programme shows how William Doherty was successfully operated on for a bladder problem which could have killed him.

At 14 weeks, a routine ultrasound scan showed abnormalities.

His mother Audrey says she was "terrified" when told that they could cause a major problem.

Further scans showed William was unable to pass urine.

Although he was just 12 centimetres long when he was 16 weeks old, doctors felt the abnormalities were so serious they needed to operate immediately.

Breathing

William's bladder was blocked so not enough amniotic fluid was being released into the womb.

Foetuses inhale and exhale the fluid and it helps to develop their lungs and teaches them how to breathe.

Audrey was one of the first women to undergo pioneering surgery at Queen Charlotte's and Chelsea Hospital to have William's blockage removed.

Professor Nicholas Fisk, who has performed the operation at least six times, said: "If there is no amniotic fluid after 17 weeks, it is certain the lungs will not develop and the foetus will always die."

The doctors inserted a telescope of one millimetre in diameter inside William's bladder to see what the problem was and how it could be treated.

"It was very, very scarey, like going into the unknown. I was worried it would harm him [William]," said Mrs Doherty.

The needle was first inserted into her womb and then into the baby.

Professor Fisk: a lack of amniotic fluid can be life-threatening

Once the needle was inside William's bladder, an endoscopic camera was passed down it to find where the blockage was.

A colleague of Professor Fisk then fed flexible wire through the needle to dislodge the blockage.

He then flushed fluid through the needle to help reopen the bladder.

One year on from the operation, scans show that William's bladder is functioning normally.

Doctors say the operation could be used to solve other foetal abnormalities.