Sleeping on your back increases the risks of a stillbirth:

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Pregnant women who sleep on their backs are more likely to have a stillbirth according to a new study.

Researchers from the University of Michigan interviewed women in the 48 hours after they had given birth at Korle Bu Teaching Hospital in Accra, Ghana.

In low-income countries like Ghana between 20 and 50 of every 1000 babies are stillborn − between two and five babies out of every 1000 births are stillborn in high-income countries, including Australia.

Researchers discovered that mothers who slept on their backs were five times more likely to have a baby with a dangerously low birth-weight, which resulted in stillbirths for some women.

"The data in this study suggests that more than one-quarter of stillbirths might be avoided by altering maternal sleep position," study author Louise O'Brien said.

"If maternal sleep position does play a role in stillbirth, encouraging pregnant women everywhere not to sleep on their back is a simple approach that may improve pregnancy outcomes."

This is not the first time sleeping position has been linked to the risk of stillbirth.

A study at the University of Sydney last year found pregnant women who sleep on their backs are six times more likely to have a stillborn baby.

There has also been evidence from New Zealand to suggest sleeping on your left side is the safest option.

Dr Adrienne Gordon, a neonatologist at the Royal Prince Alfred Hospital who led the Sydney study, told ninemsn that more work needed to be done.

"We now need to link with more physiological studies, doing things like videoing how women sleep, measuring things about the baby," Gordon said.

"There are a lot of things that can be done to confirm the biological plausibility, which would probably make people feel more confident that you need to do this as a definite preventative mechanism."

But she said it wouldn't hurt for pregnant women to sleep on their sides for now.

"The left might be more sensible because the liver is on the right and if you go to the left, you have more chance of un-obstructive blood flow in the big vessels," she said.

"But I think there is not enough evidence to say which side is definitely most beneficial. We don't have enough confirmatory things to say that, but we have enough about the back-sleeping and risk association."