A graduate student's summer project, the study is relatively small — it included only 220 women interviewed about their sleep habits just after giving birth in one hospital in Ghana.
But because Ghana has such a high rate of stillbirth, said Louise M. O'Brien, the professor at the University of Michigan's Sleep Disorders Center who oversaw the project, by Jocelynn Owusu, the conclusion seemed clear: If pregnant women avoid sleeping on their backs, 25 percent of all stillbirths in poor countries might be prevented.
The study, published online last month by The International Journal of Gynecology & Obstetrics, also found that loud snoring — which is worsened by back (supine) sleeping — raised the likelihood that a pregnant woman would get high blood pressure, a condition that may lead to a complication known as pre-eclampsia, which can kill both mother and child if left untreated or not stopped by Caesarean section.
The Ghanaian study echoed one conclusion drawn from larger studies in the United States and New Zealand, Dr. O'Brien said: that apnea in pregnant women raises blood pressure and increases risk to the baby.
The leading theory, she said, is that when a heavily pregnant woman sleeps on her back, the uterus compresses the vena cava, the blood vessel going up the spine that returns blood to the heart. That starves the fetus, leading to smaller babies and more stillbirths. Supine sleeping also closes the airways, leading to oxygen deprivation, which raises blood pressure. Closed airways lead to snoring.
"In the delivery room, when an obstetrician sees a baby in distress, they often flip the woman on to her side," Dr. O'Brien said. "But people haven't thought through the connection to the months prior to delivery."
In wealthy countries, blood pressure is lowered with drugs and apnea is prevented with breathing machines. But the drugs are little used in Africa and the machines are too costly.
Image: Pregnant woman sleeping on her side, via Shutterstock