Sleeping on side halves stillbirth risk

Stillbirth is a tragedy that no parent wants to experience. Now, new research has found a way to halve the risk of stillbirth occurring — simply by having the mother sleep on either side during the last three months of pregnancy.

The New Zealand-led international mega-study, published in The Lancet journal EClinicalMedicine, also confirmed that the risk of stillbirth associated with going to sleep on the back applies to all pregnant women in the last three months of pregnancy. Stillbirth is defined as the loss of a baby after 20 weeks of pregnancy. An estimated 2.64 million babies die before birth globally each year.

Led by Professor Lesley McCowan and PhD candidate and midwife Robin Cronin from the University of Auckland, the research team analysed all available data worldwide from five previous studies — including the 2011 Auckland Stillbirth Study led by Professor McCowan which first identified a link between mothers’ sleeping position and stillbirth risk.

The other four studies included in the meta-analysis were a multicentre study from Aotearoa, New Zealand, one from Australia, one from the United Kingdom and one from the United States, incorporating data from women of many ethnicities.

The new study, the largest to date, included 851 bereaved mothers and 2257 women with ongoing pregnancies. The chief finding was that going to sleep lying on the back from 28 weeks of pregnancy increased the risk of stillbirth by 2.6 times. This heightened risk occurred regardless of the other known risk factors for stillbirth. However, the risk is additive, meaning that going to sleep on the back adds to other stillbirth risk factors, for example, a baby who is growing poorly in the womb.

“An important finding that came out of our study was that if every pregnant woman went to sleep on her side after 28 weeks of pregnancy, approximately 6% of late stillbirths could be prevented — around 153,000 babies a year worldwide,” Cronin said.

The meta-analysis was also able to reassure pregnant women that it does not matter which side they chose to settle to sleep on — both left and right sides appear equally safe.

Professor McCowan, who is the Head of the University of Auckland’s Department of Obstetrics and Gynaecology, said women should not worry if they go to sleep on their side but wake up on their back. “This is common — just settle back to sleep on your most comfortable side. Our advice is the same whether you’re going to bed at night or lying down for a daytime nap.”

Physiological studies, carried out by the University of Auckland and funded by Cure Kids, suggest that the increased late stillbirth risk is due to a major vessel in the mother’s abdomen, the inferior vena cava, being squashed by the pregnant womb when the mother is lying on her back, reducing flow by 80%. Although the mother’s circulation responds by increasing the flow through other veins, this does not fully compensate. The mother’s aorta — the main artery which carries oxygen-rich blood from her heart, which is also partly compressed when the mother lies on her back — decreases the blood flow to the baby.

“While healthy unborn babies can compensate for the reduced blood supply, babies that are unwell or vulnerable for some other reason, may not cope,” Professor McCowan said.

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