WHEN New Zealand researchers said they had found a third of stillbirths in late pregnancy might be prevented if the mothers slept mainly on their left side, they met much scepticism from the international scientific community.

Such a simple message, to emphasise sleeping on the left, would have wide appeal if it was proven it could prevent a third of the 200 deaths of New Zealand babies in late pregnancy each year.

The researchers noted smoking and obesity were the biggest risk factors for stillbirth although nearly a third were unexplained.

Their study had found a markedly lower risk of stillbirth for women who slept on their left side, compared with the right and the back.

And those who got up to go to the toilet more frequently during the night had a lower risk than those who got up only once.

The researchers wondered whether the protection might have come from less time being spent in positions where the enlarged uterus compressed major maternal blood vessels.

Might a resulting reduced oxygen supply have been the last straw for a fetus already at risk from some unidentified factor, a problem with the placenta perhaps?

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The sceptics were soon in print, however, criticising the findings of the New Zealanders, published in the influential British Medical Journal.

"We have no idea how many women can accurately recollect how they fell asleep (can any of us?) the night before their baby died, as long after the event as three weeks," a British GP wrote derisively.

Professor Ed Mitchell defended his team's study, funded by Cure Kids, saying the researchers had asked women how they knew what position they were in when they went to sleep and got responses like "I always faced away from the door" and "I liked to sleep facing the wall". Those who couldn't recall how they had slept or were unsure were recorded in the "other" sleeping position category.

But he also freely acknowledged that because it was an observational study, it could not prove cause and effect. More studies were needed.

That was in 2011. Other stillbirth studies since have made similar findings about back-sleeping being linked to increased risk of stillbirth. Cure Kids has put money into three new studies to try to confirm whether left-side sleeping is protective.

"People are intrigued by our findings," Professor Mitchell, of Auckland University, told the Herald.

"If we are going to launch a prevention programme as we did with back-to-sleep and SIDS [sudden infant death syndrome] we have to have the findings replicated and preferably in another country to show it is consistent across communities."

Two of the new studies are similar to the ground-breaking interview-based observations made in Auckland comparing stillbirth cases with non-stillbirth mothers. One of these is being done in five New Zealand cities and the other in Britain.

The third study involves hooking pregnant women up to machines to measure various body processes including their heart rate, breathing rate, oxygen levels and the baby's heart rate.

Some of this is done in a laboratory, with the woman switching between sitting up and various lying positions; and some is done in the woman's bedroom at home, where she is also videoed to allow correlation with sleeping positions.

If these studies confirmed the protectiveness of left-side sleeping, public recommendations could be made in less than two years, Professor Mitchell said.

"What's happening is that sleep position is already changing.

Because in June 2011 when there was publicity [about the original study] midwives went away ... and said all this makes sense and started advising their women.

"I have a feeling this is going to follow the same pattern as we had with SIDS. While we were trying to get agreement, people were already advising parents to change the baby's sleeping position. SIDS mortality decreased before the launch of the information programme," Professor Mitchell said.

"We are quite excited about it in the sense that, given that stillbirths in New Zealand have decreased only very slightly over the last 20 years despite the big increase in the quality of obstetric care and the increasing caesarean section rate, it hasn't made much impact on avoiding stillbirths. This could actually be the biggest jump forward."