She said Māori women were more likely to go into pre-term birth than non-Māori.

Based on this survey, the authors do not see climbing as being a risk factor for pre-term birth.

Among other variables associated with the current pre-term birth were previous spontaneous pre-term births, suggesting their special risk value.

The study showed that chorioamnionitis is a factor in asthma independent of pre-term birth, Getahun said in a telephone interview.

Thirty-four percent of mothers whose babies died from spontaneous pre-term birth were smokers, higher than rates of smoking for mothers overall.

On a yearly basis there were 152 neonatal deaths in 2013, of these, 49 died from spontaneous pre-term birth.

Pre-term deaths The report found that spontaneous pre-term births were the second highest cause of perinatal deaths in New Zealand.

The findings from the overseas studies - and others that may follow - could provide vital breakthroughs into preventing pre-term births, Dr Wise said.