Mega Study Confirms Pregnant Women Can Reduce Risk of Stillbirth by Sleeping On Their Side

By Lesley McCowan, University of Auckland and Robin Cronin, University of Auckland

A New Zealand-led international study published on 1 April 2019 provides the strongest evidence yet that women can more than halve their risk of stillbirth by going to sleep on either side during the last three months of pregnancy.

This mega study (known as individual participant data meta-analysis) has also confirmed the risk of stillbirth associated with sleeping on the back applies to all pregnant women in the last trimester of pregnancy.

Risk factors

In New Zealand, 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, and around 300 babies are stillborn in Aotearoa New Zealand each year. About one in every 500 women in New Zealand will experience the tragedy of a late stillbirth and lose their baby during or after 28 weeks of pregnancy.

We have analysed all available data worldwide from five previous studies, including our earlier research, the 2011 Auckland Stillbirth Study, which first identified a link between mothers’ sleeping position and stillbirth risk. The main finding in the mega study, which included information from 851 bereaved mothers and 2,257 women with ongoing pregnancies, was that going to sleep lying on the back (supine) from 28 weeks of pregnancy increased the risk of stillbirth 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.

Importantly, our mega study has shown that if every pregnant woman went to sleep lying on her side after 28 weeks of pregnancy, approximately 6% of late stillbirths could be prevented. This could save the lives of about 153,000 babies each year worldwide.

Existing common risk factors for late stillbirth are not easily modifiable. They include advanced maternal age (over 40), obesity, continued cigarette smoking and an unborn baby that is growing poorly, especially if the poor growth is not recognised before birth. Women also have a higher risk during their first pregnancy, or if they have already had three or more babies. Women of Pacific and South Asian ethnicity also have an elevated risk of late stillbirth, compared with European women.

If modifiable risk factors can be identified, some of these baby deaths could be prevented. Importantly, our mega study has shown that if every pregnant woman went to sleep lying on her side after 28 weeks of pregnancy, approximately 6% of late stillbirths could be prevented. This could save the lives of about 153,000 babies each year worldwide.

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