The advice for pregnant women to sleep on their sides during their third trimester isn't a new one. But a recent study, the largest of its kind, says that how you fall asleep during late pregnancy can halve the risk of stillbirth.
The researchers estimate that about 130 babies' lives in the U.K. (where the study was conducted) could be saved every year if women avoided sleeping on their backs. One in 225 pregnancies in the U.K. ends in stillbirth. (For scale, in the U.S., stillbirth affects about one in every 100 pregnancies, according to the Centers for Disease Control and Prevention.)
The MiNESS study, published in the British Journal of Obstetrics and Gynaecology, found that out of more than 1,000 women, those who slept on their back in the last three months of pregnancy had at least twice the risk of stillbirth compared to those who slept on their left side. Factors such as the duration of pregnancy after 28 weeks, the size of the baby or the mother's weight did not affect the link between their sleep position and stillbirth rates. The MiNESS study confirms similar findings from smaller studies, including ones in New Zealand and Australia.
While it's not certain why certain sleep positions increase the risk of stillbirth, experts think 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. New research published in the Journal of Physiology was the first to monitor unborn babies and women's sleep positions overnight. It showed that fetuses were only in an active state when their mothers were sleeping on their sides.
Pregnant women already lose sleep over so many issues, so is this one really worth worrying about?
"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,'" Alexander Heazell, clinical director at the Tommy's Stillbirth Research Center in Manchester tells the BBC.
Heazell suggests women pay attention to the position they fall asleep in, as that's the position people tend to be in longer than any other. If you find yourself waking up on your back, relax and just roll back on your side. How you end up after your sleep or nap isn't something you can control.
Tommy's, the largest charity funding research into the causes of miscarriage, stillbirth and premature birth, doesn't believe that a baby's death is just "one of those things." Their mission is to give every parent the best possible pregnancy outcomes.
"There are few risk factors for stillbirth that can be easily changed, but this study is looking at identifying how mothers may be able to reduce their risk," the researchers wrote.
We get that for some pregnant women, they're lucky if they can get sleep on any side. Any sleep is much appreciated, especially when you're counting the days until Baby comes and you'll be running on fumes. With studies like these piling on, it can be hard to remember that every pregnancy is different.
Acknowledge that. But also pay attention to how you feel. If you feel short of breath or lightheaded while sleeping on your back, try what you can to sleep on your side.
Maybe sleep with your legs and knees bent, with a pillow between your legs, as the American Pregnancy Association suggests. You can also prop yourself up with pillows to keep yourself from rolling onto your back. And don't brush off pregnancy pillows—they can be serious game-changers!