Each year 5000 babies in New Zealand are born too soon, putting them at increased risk of health problems.
Now researchers in Auckland are developing a blood test that would predict premature births so at-risk pregnant women don't get caught by surprise.
When baby Reuben was born at just 24 weeks, it was touch and go whether he would survive. He was tiny, weighing just 665 grams - little more than a block of butter.
"You could hold him in one hand, but we couldn't actually hold him, we had to wait till he was 10 days old because his skin was paper thin and his eyes were fused shut, so it was a long 10 days to actually get to hold my baby," says Reuben's mother Rachel Friend.
Despite the odds, he made it, and he's now a determined little four-year-old.
This week, Reuben is due to have his final hospital check-up.
Most babies born before 24 weeks don't survive.
Preterm babies born after 24 weeks have a greater risk of problems with learning and development, cerebral palsy, growth, and later adult diseases such as obesity and diabetes.
For every 100 babies born full term, eight will be born too early, and will have to go to hospital. About 60 percent of preterm births occur without warning. And currently, there is no reliable way to predict it.
Now researchers in Auckland believe they've found a promising blood test which could identify mothers at high risk.
"There is a pattern, there is a specific message, that seems to be passed through the blood, that they can isolate from the mums which indicates at the least the chances of, or the risk of spontaneous pre-term birth occurring," says Dr Justin O'Sullivan, from the Liggins Institute.
Clinicians say it's an exciting development.
"We've found marked differences in mothers who go on and have an early spontaneous pre-term birth and mothers who give birth at term," says Prof Lesley McCowan, of Auckland University.
"And if we can identify mothers who are at high risk we can potentially provide specialised care which reduces their chance of having a premature birth."
They're now looking to fund a larger study to confirm their results so they can help those like Ms Friend and her son.