Surgeons have developed an operation to repair a potentially fatal abnormality in babies before they are born.
The condition is relatively common
Some babies develop a hole in their diaphragm which leads to their gut or liver moving into their chest, and squashing their lungs.
The new operation, pioneered at London's King's College Hospital, has reduced death rates in the most at risk by 50%.
Details are published in Ultrasound in Obstetrics and Gynecology.
The condition, known as a congenital diaphragmatic hernia (CDH), is a relatively common foetal abnormality - occurring in about one in every 3,000 pregnancies.
It appears to happen spontaneously, and does not have genetic cause.
Usually, the diaphragm - a muscular sheet which separates the chest from the abdomen - is fully formed by about nine weeks of development.
But in this condition, a small hole remains, and as the foetus develops the contents of the abdomen, the gut or the liver, force their way through the gap, and up into the chest.
This a problem because, unlike the abdomen, which can expand, the chest is a boney box.
Therefore, when the gut contents enter the chest cavity they compress the lung tissues, and prevent them from developing properly.
As a result, around 50% of babies born with the condition cannot breathe properly, and die.
The new technique is designed for those babies most at risk.
It has been developed by Professor Kypros Nicolaides, at King's, in collaboration with doctors at University Hospital Gasthuisberg, Leuven, Belgium, and Vall d'Hebron Hospital, Barcelona.
Blocking the windpipe
The operation, known as fetoscopic tracheal occlusion, involves inserting a balloon down the foetal windpipe when the foetus is at around 26 weeks of development.
This stops fluid generated in the lungs from escaping into the mouth, and out into the amniotic fluid surrounding the developing baby.
The fluid contains chemicals which stimulate growth of the lung tissue, and provides vital nutrients to speed the process.
Blocked from leaving the lungs in the normal way, the fluid stimulates the lung tissue to develop to such an extent that it begins to expand, and eventually to push the gut contents back through the hole in the diaphragm.
Initially, the balloon was removed from the baby's windpipe when the child was born, but the surgeons have now switched to a policy of removing it about a month before full term. This allows the child to be born naturally, rather than through a Caesarean section.
Professor Nicolaides told BBC News Online that three of the first 10 babies who underwent the surgery survived, but the six of the next 11 pulled through.
He is confident that 60-70% of babies most at risk will now survive after undergoing surgery.
He said: "This focuses on an important aspect of foetal medicine which is not to do with searching for abnormalities in order to destroy foetuses, but to diagnose them as early as possible and to develop minimally invasive procedures to correct them."
Professor Stuart Campbell, Editor of Ultrasound in Obstetrics and Gynaecology, said: "This relatively common foetal abnormality can be devastating to parents who until now could be offered little hope that their babies would survive.
"With the help of better scanning techniques we can accurately diagnose most foetal anomalies and we are now moving into the next phase where some of the abnormalities can be successfully treated in the womb."
1 - If the diaphragm does not fully form the organs below force themselves upwards into the chest cavity leaving no room for the lungs to grow.
2 - Doctors insert an air balloon into the foetus' windpipe, blocking the airway. Growth fluids produced inside the lungs are trapped causing the lungs to inflate to the correct size.
3 - The air balloon is removed about one month before birth, freeing up the airway to allow a normal delivery.