Sleeping on your back during late pregnancy may be comfortable but a new study finds that it may cause problems for the fetus. The study conducted by researchers at the University of Auckland, New Zealand, is the first to monitor unborn babies overnight and at the same time record the mother’s position during sleep.
The researchers set up an infrared video camera to record pregnant women’s position as they slept, while also continuously recording the heart rate of the women and fetus overnight using an ECG device.
When the mother slept on her back, the fetus was less active. Fetal activity is one measure of its wellbeing. Fetuses were only in an active state when the mother was on her left or right side. When the mother changed position during sleep, for example from her left side to sleeping on her back, the baby quickly changed activity state and became quiet or still.
“In the situation where the baby may not be healthy, such as those with poor growth, the baby may not tolerate the effect of maternal back sleeping,” said Peter Stone, one of the lead investigators on the study, in a news release. We are suggesting that there is now sufficient evidence to recommend mothers avoid sleeping on their back in late pregnancy, not only because of the epidemiological data but also because we have shown it has a clear effect on the baby.”
The Auckland study, published in The Journal of Physiology, involved 30 pregnant women at 34-38 weeks gestation, all healthy with healthy babies. The researchers are now investigating pregnancies where the fetus is not growing properly or the mother has reported decreased fetal movements, as both situations have been associated with an increased risk of stillbirth.
This is the first study to monitor unborn babies overnight and at the same time record the mother’s position during sleep. Previous studies have shown that the sleep position of women in late pregnancy can related to an increased risk of late stillbirth (after 28 weeks gestation).
Previous studies support findings
In one such study, published in 2013, pregnant women in Ghana who slept on their back were at an increased risk of stillbirth compared to women who did not sleep on their back, according to research led by a University of Michigan researcher.
In that study, published in the International Journal of Gynecology and Obstetrics, researchers found that supine sleep — sleeping on the back — increased the risk of low birth weight by a factor of 5 and that it was the low birth weight that explained the high risk for stillbirth in these women.
Stillbirth is a traumatic event that occurs in about 2-5 babies out of every 1,000 babies born in high-income countries. In low income countries, such as those in Africa, about 20-50 babies out of every 1,000 babies are stillborn.
“But if maternal sleep position does play a role in stillbirth, encouraging pregnant women everywhere not to sleep on their back is a simple approach that may improve pregnancy outcomes,” said Louise O’Brien, Ph.D., M.S., associate professor in U-M’s Sleep Disorders Center.
Sub-Saharan Africa has the highest rate of stillbirth in the world and little progress has been made in reducing those deaths.
“In Ghana, inexpensive interventions are urgently needed to improve pregnancy outcomes. This is a behavior that can be modified: encouraging women to avoid sleeping on their back would be a low-cost method to reduce stillbirths in Ghana and other low-income countries,” said O’Brien.