We found that abnormal heart rate characteristics preceded visible symptoms by as much as 24 hours.

Dr Randall Moorman Researcher

The infants were at high risk for infection because of low birthweight, being premature or having been in hospital for more than two weeks.

The researchers said the technique was also effective in a second study of 350 babies at other hospitals in the US.

Dr Griffin said: "The characteristics we see in newborns who are developing infection are similar to the abnormalities we see in cases of fetal distress.

"Our point of view is that newborns are fetuses that have graduated into a new environment and are experiencing stress from different factors, like bacterial infections, but have a similar physiological response."

Dr Moorman added: "We found that abnormal heart rate characteristics preceded visible symptoms by as much as 24 hours.

"That means something was happening early that doctors would not yet be aware of.

"By the time signs and symptoms show and prompt doctors to do blood tests, sepsis can have quickly developed to a severe level."

'No difference'

Dr Vivienne van Someren, a consultant paediatrician and senior lecturer in child health at the Royal Free Hospital in London, said it was unlikely the new technique would make a big difference in the outcome for preterm babies.

She said: "The method would act as an early warning sign that a baby was 'going off' and hence might be useful, but would not tell you what was wrong with the baby."

She added: "The method would add to the cost and complexity of neonatal intensive care."

She said more trials would be needed, focussing on whether babies monitored in this way and treated on the basis of this early warning, did better than those monitored conventionally.