Scientists are a step closer to understanding the trigger for pre-term birth and believe they may have found a drug to prevent a baby from being born too early.

A new drug that could save parents the heartache of losing their baby because they were born too early has shown promise, say Australian scientists.

In efforts to prevent pre-term birth, researchers from the University of Adelaide have successfully tested the drug, known as (+) naloxone, on mice.

The encouraging results have been published in the Nature journal Scientific Reports.

Lead author and director of the Robinson Research Institute, Professor Sarah Robertson, says they are now a step closer to understanding the inflammatory mechanisms that lead to premature births and how they can be suppressed.

"By the time the conditions for pre-term birth have already arisen, it's often too late for current treatments to do anything about it," she said. "What we really need is to stop the train at the station, as it were, before it can head down that track. Once it's left the station it's usually too late to stop it."

Pre-term birth, that is a baby born at less than 37 weeks gestation, is the major cause of death in children under five years of age, accounting for 1.1 million deaths across the globe annually.

The main cause of pre-term birth is bacterial infection, in around 50 per cent of cases, and physical injury or stress that causes damage to the placenta.

Twins or triplets are also commonly born pre-term.

Each of these is associated with what researchers describe as an "inflammatory cascade", which activates the mother's immune response and ultimately leads to spontaneous pre-term birth.

This inflammatory cascade is caused by an immune receptor known as Toll-Like receptor 4 (TLR4) that produces effects harmful to pregnancy.

"TLR4 is a trigger of spontaneous pre-term birth," said Prof Robertson. "For this reason, we wanted to test a drug known for its ability to block the actions of TLR4, to see if that would also prevent pre-term birth."

It was (+)-naloxone that protected the mice treated with the drug against bacterial induced pre-term birth. It also protected the mice against stillbirth and offspring death shortly after birth.

"The babies born to mothers treated with (+)-naloxone developed normally and were mostly indistinguishable from those born to the control group," said Prof Robertson.

More research is now under way to determine if the drug or similar drugs could be used in human clinical trials.

If so, they would likely be used in combination with antibiotics, said Prof Robertson.