Researchers compared the sleeping practices of more than 1,000 women in Britain, 291 of whom suffered a stillbirth in the third trimester and 733 of whom had a live birth during the same period. The study found that women sleeping on their backs had 2.3 times the risk of stillbirth. The results add to earlier findings in recent years from smaller studies in New Zealand and Australia.
Researchers behind the new study said they can't explain with certainty why sleeping position might affect stillbirths chances, but they pointed to data suggesting that when a pregnant woman lies on her back, the weight of the womb can impose pressure on the vessels carrying blood and oxygen to the baby.
Another hypothesis raised by the researchers is that sleeping on your back can increase the possibility of impaired breathing.
The lead researcher, Alexander Heazell, clinical director at the Tommy's Stillbirth Research Center at St. Mary's Hospital in Manchester, said women should try to fall asleep on their side and not worry too much if they wake up on their back.
"What we don’t want is for moms to wake up and see their on their back and think, 'I’ve done something terrible to my baby,'" Heazell said. "You can’t control the position you wake up in. And the position you fall asleep in is the position you hold longest in sleep. So that's the most important thing."
Heazell said there is a deep need for more research on stillbirths and miscarriages. When it comes to stillbirths in the Western countries, he said, "There is a huge amount of this attitude of 'Well, it’s just one of those things' or 'it wasn't meant to be.' Just responding with platitudes."
He argued, "That kind of fatalistic attitude is a problem. It's been holding back research."
If heeded, the new findings could have a significant effect on stillbirth rates, the researchers say. Combining their data with birth statistics, they estimate that if pregnant women stopped sleeping on their back during the last trimester, stillbirths in Britain could decrease by 3.7 percent.
Stillbirths are a common problem in the United States. Stillbirths occur roughly 3 in every 1,000 births (compared with Britain's 3.5 in every 1,000 births). And each year about 24,000 babies are stillborn in the United States, according to the Centers for Disease Control and Prevention.
Better medical technology and improvements to prenatal care have reduced the number of late-term stillbirths in the past few decades, but miscarriages earlier in pregnancy have remained roughly the same.
In Britain, the nonprofit Tommy's Stillbirth Research Center launched a campaign Tuesday in response to the new findings to encourage pregnant women to sleep on their side. They included these tips to help women in their sleep:
- 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.