Scientists believe research which may have identified the trigger for some premature births could help reduce the number of babies born early.

Around 50,000 babies each year are born prematurely - 7% to 10% of all pregnancies - increasing their risk of long term physical or mental disability.

Two thirds of babies who die shortly after birth are born premature.

Any research that can identify the trigger for premature birth and therefore reduce it could only be good Bliss spokeswoman

The cause of premature births has remained a mystery.

However, researchers at the University of Newcastle believe it could be linked to the production of a protein which keep the muscles of the womb relaxed during pregnancy, so the baby can grow.

Levels of the protein, called G alpha S, are maintained during pregnancy, then fall during labour.

'Lasting benefit'

Premature birth occurs when levels fall too early in the pregnancy, before the baby is fully developed.

The Newcastle team, funded by the charity Action Research and the Wellcome Trust, says that if it can find ways of maintaining levels of the protein, premature births could be prevented.

Dr Nick Europe-Finner, who is leading the research, told BBC News Online: "We're trying to understand how the uterus remains relaxed, to look at the mechanics that cause relaxation, and if we can understand those, we can understand going into labour early."

He added: "Understanding what triggers off the process of labour and preventing it from happening prematurely will be of lasting benefit to generations of babies."

Stressful time

A spokeswoman for Bliss, the charity for premature babies, told BBC News Online: "Care of premature babies and sick newborn babies is improving all the time.

"But some babies are still born too soon, or to small, to survive.

"Obviously it's not the best start in life for the babies, and it's an incredibly stressful and traumatic time for parents.

"Any research that can identify the trigger for premature birth, and therefore reduce it, could only be good."