Back sleeping in third trimester doubles stillbirth risk, study finds

Sleeping on the back during late pregnancy doubles the risk of stillbirth.
Sleeping on the back during late pregnancy doubles the risk of stillbirth. Photo: Shutterstock

The risk of stillbirth is doubled if women fall asleep on their backs in the third trimester. That's according to new research, which has the potential to save the lives of over 100,000 babies around the world each year.

The findings, published in BJOG: An International Journal of Obstetrics and Gynaecology, come from the Midlands and North of England Stillbirth Study (MiNESS), the largest examination of maternal sleep position and risk of stillbirth to date. As part of the research, the team examined 291 pregnancies that ended in stillbirth and 735 women who had a live birth. Women were questioned about their sleep practices before pregnancy, in the four weeks prior to, and on the night before the stillbirth, or the night before the interview for those in the control group.

And the results were clear: women who had a late stillbirth were 2.3 times more likely to report lying on their back when they went to sleep the night before losing their baby. "This study suggests that 3.7 per cent of stillbirths after 28 weeks of pregnancy were linked with going to sleep lying on the back," the authors note. There was no difference in risk, however, between sleeping on the right or left side of the body.

But they weren't the only key findings. "Other sleep behaviours associated with late stillbirth included short and long sleep duration on the last night, getting up to the toilet only once or not at all on the last night, and daytime napping every day," the researchers write.

The study is the fourth now to demonstrate the increased risks associated with expectant women going to sleep on their backs, including Australian research from 2015, involving women from Sydney metropolitan hospitals.

"We believe that identifying, and avoiding, risk factors that are strongly associated with stillbirth will reduce the number of babies who are stillborn," said lead author Professor Alexander Heazell. "The MiNESS results have implications as they indicate that if women go to sleep on their side in late pregnancy rather than on their back there could be 3.7 per cent reduction in stillbirth."

While it is unclear exactly why falling asleep on the back is associated with an increased risk of stillbirth, there are several theories. Earlier this year, the same researchers published work indicating that when a mother slept on her back, her baby was less active. In fact bubs, were only active when expectant mamas slept on their left or right side. The authors also explain that during the third trimester when a mum is lying on her back, the combined weight of bub and the womb puts pressure on the main blood vessels that supply the uterus. This can then restrict blood flow/oxygen to the baby. 

"Public health education should be developed recommending that women in the third trimester do not settle to sleep supine, especially after 37 weeks," they write.

Experts provide the followings tips for going to sleep on your side - both during day and night - in the last three months of pregnancy:

  • Put pillows behind you to prevent falling on your back. It won't prevent you being on your back for certain but is likely to make it more uncomfortable.
  • If you wake up for any reason during the night, check your position and go back to sleep on your side.
  • If you are likely to nap during the day pay the same attention to sleep position during the day as you would during the night. 

There are six stillborn babies a day in Australia. In 40 per cent of the cases, the cause of death is unknown.