A blood test to predict the risk of premature birth as early as 18 weeks into pregnancy can detect signs even before symptoms present, according to international researchers.
The test picks up six different genes expressed in the mother's blood. The genes are related to the communication between white blood cells, which are associated with early labour.
Craig Pennell from the University of Western Australia's school of womens' and infants' health said the blood test was the most precise to date - able to predict the risk of early delivery with 86 per cent accuracy.
"The exciting thing about this is it tells you if you are at risk of pre-term birth, then you can make yourself available to interventions and care," lead researcher and associate professor Pennell said.
"Conversely if it suggests that everything is normal, then the woman can proceed with a low-risk model of care."
There are about 26,000 premature births in Australia each year. Premature births, meaning delivery before 37 weeks gestation, is the main cause of death and disability of babies globally according to the World Health Organisation. More babies die from pre-term births than infection, including AIDS and malaria.
Associate professor Pennell said the blood test meant women at risk of delivering early could benefit from earlier intervention, including accessing specialist care sooner and beginning treatments known to reduce the risk of pre-term birth, such as progesterone medication.
Currently the best test for premature birth risk is a vaginal swab and a cervical ultrasound, which has an accuracy rate of about 65 per cent.
"So while it's not a perfect test, 86 per cent is a huge improvement on what exists currently," he said. "The best way to reduce the number of pre-term births is to know who is going to deliver early, so that they can get access to the right type of care."
Scientists have known for more than a decade that white blood cells are a marker of the onset of labour. However it hasn't been known which genes are turned on and off, and how they are expressed weeks to months before women go into labour. These are changes which take place well before any symptoms are expressed.
The rate of premature births in Australia has increased over the past decade due to a combination of factors, including older mothers, the growing rate of infertility treatment, the rising number of multiple births and increased monitoring.
Associate professor Pennell said it was still likely to be five years before the test, which would be conducted with the anatomy scan in the middle part of pregnancy, would be available for expectant mothers.
The findings by researchers from the University of Western Australia as well as the universities of Toronto, Alberta and Calgary have been published in the journal PLOS One.
