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29th May 2019
07:00am BST

As for why this position is deemed riskier in terms of the baby's health, researchers speculate it could be because when a woman is lying flat on her back, the size of the baby and the uterus can compress the blood vessels responsible for sending blood to the uterus, potentially restricting blood flow and oxygen to the baby.
Another study published in the Journal of Physiology recently looked at unborn babies and women's sleep positions overnight,, and showed that fetuses were only in an active state when their mothers were sleeping on their sides.
But experts are also keen to point out that pregnant women shouldn't stress too much if they have fallen alseep on their side, but wake up on their backs.
"What I don't want is for women to wake up flat on their back and think, 'Oh my goodness, I've done something awful to my baby,'" explains Alexander Heazell, clinical director at the Tommy's Stillbirth Research Center in Manchester to the BBC.
Instead, he suggests, women should pay more attention to position they fall asleep in, as this is the position people tend to sleep in longer than any other.
If you are pregnant and worried about rolling onto your back while you are asleep, a pregnancy pillow to prop you up could be of good help, making sure you stay sleeping on your side for the night.