TUESDAY, Sept. 10, 2019 (HealthDay News) -- Pregnant women are often told to sleep on their left side to reduce the risk of stillbirth, but new research suggests they can choose whatever position is most comfortable through most of the pregnancy.
"We can reassure women that through 30 weeks of pregnancy, different sleep positions are safe," said study lead author Dr. Robert Silver, chairman of obstetrics and gynecology at the University of Utah School of Medicine.
Silver said the study didn't include women past 30 weeks, so researchers can't make any definitive statements about the last weeks of pregnancy.
The research is being published in the October issue of Obstetrics & Gynecology and ahead of print online Sept. 10.
Why have women been encouraged to sleep on their left sides, particularly since sleeping during pregnancy can already be uncomfortable and difficult?
There is a known phenomenon that can limit blood flow during labor if a woman lies flat on her back, explained Dr. Nathan Fox, associate clinical professor in obstetrics, gynecology and reproductive science at the Icahn School of Medicine at Mount Sinai in New York City.
At the end of pregnancy, a woman's uterus and the baby take up a large portion of the body. If a woman lies flat on her back during labor, it's possible to compress blood vessels underneath. That could lead to decreased circulation and a drop in the baby's heart rate. To counteract this, women are positioned slightly to the side, said Fox, who coauthored an editorial published with the study.
Past researchers suspected that maybe a similar thing happens in women who have stillbirth, when a fetus dies in the womb. Previous studies asked women who'd had stillbirth to try to recall how they slept while pregnant. Those studies found a significant link between certain sleep positions, such as on the back, and stillbirth.
But Fox explained that it's difficult for people to remember what they did in the past, and even more so after a tragedy like stillbirth.
The new study was designed differently. Just over 8,700 women were asked at several points during pregnancy about their sleep positions. About one-third also underwent a sleep study where their positions were recorded, Silver said.
Researchers looked for a number of adverse pregnancy outcomes, including stillbirth, high blood pressure disorders, and having a baby small for its gestational age. Twenty-two percent of women in the study had these outcomes.
Yet when researchers compared these pregnancy complications to a woman's sleep position, they didn't find a link.
Silver said this research needs to be done in later pregnancy to see if the results are the same.
"Women should try to sleep in whatever position is most comfortable for them," Fox said. "And we [the medical community] need to be cautious when giving recommendations about what to do in everyday life. Consider what is the evidence supporting that recommendation."
He noted public health campaigns encouraging women to sleep on their left side during pregnancy.
"It's hard to forecast the outcome of such recommendations where people have good intentions, like preventing stillbirth. The intervention may seem simple or benign, but it can potentially inconvenience a lot of people. Making sleep more difficult in pregnancy may have an impact on a woman's health. And, if something horrible happens, it's difficult to convince women that it wasn't somehow their fault," Fox said.
His editorial concluded: "This harm to women already suffering from sadness and despair must not be minimized."
Learn more about the body changes and discomforts of pregnancy, including sleep issues, from the U.S. Office on Women's Health.