During pregnancy, sleeping on your back may be a bad idea.
Previous studies have found that sleeping in a supine position causes compression of veins and arteries that can lead to a reduction in blood flow to the placenta severe enough to double the risk for stillbirth after 28 weeks of gestation.
Now a new study, in JAMA Network Open, concludes that supine sleeping is also associated with low birth weight in full-term babies.
Of 1,760 pregnant women in the analysis, 57 went to sleep lying on their backs. (The initial sleep position is the one maintained for the longest time during the night.)
After controlling for age, body mass index, previous pregnancies, hypertension, diabetes and other factors, they found that compared with those sleeping in other positions, women who slept on their backs had babies who were three times as likely to be in the lowest 10th percentile for birth weight.
“It’s a small number of pregnant women who go to sleep on their backs — only about 3 percent,” said the lead author, Dr. Ngaire H. Anderson, a senior lecturer in obstetrics and gynecology at the University of Auckland. “But we are keen to encourage the message that sleeping on one’s side is a way to optimize the baby’s health, both in reducing stillbirth and optimizing the baby’s growth.”