For tiny Daisy Salter, every extra day in mum's belly was vital.

The Grey Lynn 8-month-old was born when her mother, Katie Salter, was just 23 weeks and two days pregnant.

The family, which also includes dad Neil and big sister Ila, 5, had some warning Daisy might come early.

Ila was born at 31 weeks and three days and Katie Salter put herself on bedrest six weeks before Daisy's birth after being warned her second baby was also coming early.

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But not everyone has that warning, and the couple have backed an Auckland University Medical School and Liggins Institute study developing a blood test to predict premature birth.

"We were quite closely monitored, but not everybody is. Every day or week makes a difference," Neil Salter said.

"It can be the difference between life and death, or health and ill-health."

At just over 23 weeks, Daisy made it over the survival threshold by only a few days, he said.

Their baby girl weighed just 545g when she was born on June 4 last year and spent her first three weeks on a ventilator. She went home from hospital 102 days after her birth.

Daisy's start was probably the scariest time of her life, and anything to prevent other parents and babies going through the same thing was "incredibly valuable", Katie Salter said.

Daisy still needed oxygen at night and it was too early to know how her early start may have affected her future health and development.

But she was meeting milestones for her real age, 4-and-a-half months, and now weighed 6.2kg, which put her in the 25th percentile for her age, Katie Salter said.

And she was doing the job all babies do - bringing joy to her parents' lives.

"She's a special girl - she's our miracle."

Daisy Salter, pictured this month. Photo / Supplied
Daisy Salter, pictured this month. Photo / Supplied
Daisy Salter, pictured with her mum, Katie Salter, following her premature birth. Photo / Supplied
Daisy Salter, pictured with her mum, Katie Salter, following her premature birth. Photo / Supplied

Most premature births occur spontaneously

Globally, around 10 per cent of births are premature - before 37 weeks. In New Zealand the figure is around 8 to 9 per cent - more than 5000 babies a year.

Around 60 per cent of premature births occur spontaneously, often in women with no history or warning. The remainder have an induced labour, a planned caesarean or an emergency caesarean before the onset of labour.

The deaths of around 50 newborns and 25 stillborn deliveries a year are attributed to spontaneous premature birth in New Zealand.

Premature birth carries numerous health risks, including vision and hearing problems, cerebral palsy, learning and development difficulties and, in adult life, obesity and diabetes. The earlier a baby is born, the greater the risks; few survive if born earlier than 24 weeks.

"If we can develop a reliable blood test to identify women who will have a spontaneous pre-term birth by mid-pregnancy, this has potential to lead to a huge advance in clinical practice," McCowan said.

Women identified by the test could be referred to specialist clinics that already exist for those known to be high risk for preterm birth because of factors such as having had a previous premature baby.

Tests for preterm birth can be done on women at risk, such as measuring the length of the cervix and vaginal swabs.

Treatments are available - depending on each woman's circumstances - such as placing a suture around or through the cervix to clamp it shut, or progesterone hormone therapy. They can delay the onset of labour, but are not considered 100 per cent guaranteed.

The potential biomarker found in the pilot study was derived from analysis of women's micro-RNA. These are RNA molecules that play key roles in the regulation of gene expression. They are involved in the development of, and protection from, various diseases.

Daisy Salter a few weeks after being born prematurely. Photo / Supplied
Daisy Salter a few weeks after being born prematurely. Photo / Supplied

Larger study now planned

Micro-RNA "fingerprints" have also been identified as potential markers for the weak-bone condition osteoporosis, cancers and the pregnancy complication pre-eclampsia.

Having identified the preterm birth biomarker, the Auckland University researchers are now doing a larger study to confirm their results. Like the pilot study, it is based on blood samples given by more than 2000 women in their first pregnancy in a series of studies that began in 2004.

The new study would include results from blood tests at 15 weeks into pregnancy.

McCowan said that if they proved predictive like the 20-week findings, this would be "even more exciting, because there's greater potential to try to modify things".

The research began with a grant from the Auckland Medical Research Foundation and now the Auckland Harbourside Rotary Club will donate money raised at its annual Chinese New Year charity gala ball, to be held on Saturday at SkyCity.

Rotary representative Donald Sew Hoy said: "We are highly excited about the opportunity to team up with the foundation to raise funds to support this research.

"Success of this project will benefit not only New Zealand, but also the whole world, and we're proud and honoured to be asked to assist."

To book tickets at the ball, go to http://bit.ly/2lFIgcl