A pregnant woman's risk of a stillbirth appears to rise if she sleeps on her back during her third trimester of pregnancy, according to a study published last week in the British Journal of Obstetrics and Gynaecology (BJOG).
According to the Washington Post's "To Your Health," the study provides the clearest evidence to date of the significant effects sleeping conditions during pregnancy might have on a fetus.
Stillbirths in the US
Stillbirths occur in approximately three in every 1,000 U.S. births, "To Your Health" reports. According to CDC, about 24,000 U.S. infants are stillborn annually. CDC research and other studies have found the United States in recent years has significantly lagged in reducing the rate of stillbirths when compared with other countries. Improvement in technology and prenatal care have led to a decrease in late-term stillbirths over the past few decades, but the number of early miscarriages has remained about the same, according to "To Your Health."
For the study, researchers interviewed more than 1,000 pregnant British women—including 291 who had a stillbirth and 733 who had a live birth in their third trimesters. The researchers compared the women's sleeping practices and examined whether an association exists between how a pregnant woman sleeps and stillbirths. The study is the largest of four similar studies—including smaller studies in Australia and New Zealand—that show a link between a pregnant woman's sleep position and stillbirths after 28 weeks of pregnancy.
The study suggests that about 3.7% of stillbirths after 28 weeks of pregnancy were linked to pregnant women sleeping on their backs. In particular, the researchers found pregnant women who fell asleep on their backs had 2.3 times the risk of a stillbirth compared to pregnant women who went to sleep on their left sides.
The researchers found that the duration of the pregnancy after 28 weeks, the fetus' size, and pregnant women's weight had no effect on the link between sleep position and stillbirths. Further, the researchers found women who went to the bathroom at least once during the night had a reduced risk of stillbirth.
The researchers said they cannot definitively explain the association between a pregnant woman's sleeping position and the chances of a stillbirth, though they noted that research suggests the weight of a woman's womb can place pressure on the vessels carrying blood and oxygen to the fetus when a pregnant woman lies on her back.
The researchers estimated that if pregnant women did not sleep on their backs during their last trimesters of pregnancy, stillbirths in England could decrease by 3.7%.
Alexander Heazell, the study's lead researcher and a clinical director at the Tommy's Stillbirth Research Center at St. Mary's Hospital, said pregnant women should try to fall asleep on their sides but should not feel too concerned if they wake up on their backs. Heazell said, "What we don't want is for moms to wake up and see [they're] on their back and think, 'I've done something terrible to my baby.'" He added, "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 called for further research on stillbirths and miscarriages, saying when it comes to stillbirths in Western countries,"[t]here is a huge amount of this attitude of 'Well, it's just one of those things' or 'it wasn't meant to be.'" He said, "That kind of fatalistic attitude is a problem. It's been holding back research."
Edward Morris of BJOG said the new study is "extremely welcome" and "important" because it "adds to the growing body of evidence that sleep position in late pregnancy is a modifiable risk factor for stillbirth" (Wan, "To Your Health," Washington Post, 11/20; Berson, Sacramento Bee, 11/20; BBC News, 11/20; Heazell et al., BJOG, 11/20).
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