such as stillbirth, small-for-gestational-age (SGA) newborns, and gestational hypertensive disorders. The finding, published in the October issue of Obstetrics & Gynecology, conflicts with previous retrospective case-control studies that suggested left-side sleeping may lead to reduced risk. The disagreement may be due to the prospective nature of the new study, which followed 8,706 women over 4 years.
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Right-side or back sleeping had attracted suspicion because of its potential to compress uterine blood vessels and decrease uterine blood flow, and various public health campaigns urge pregnant women to sleep on their left side. Although case-control studies backed up those worries, those retrospective approaches can suffer from limitations including recall bias, in which grieving mothers overreport suspect sleeping behaviors, perhaps in search of an explanation for their loss.
Prospective analyses can counter some of those limitations. The researchers, led by Robert Silver, MD, of the University of Utah, Salt Lake City, conducted a secondary analysis of the nuMoM2b study, examining adverse pregnancy outcomes and risk factors. It was a multicenter observational cohort study of 8,706 nulliparous women with singleton gestations who completed two sleep questionnaires: one between 6 and 13 weeks of gestation, and one between 22 and 29 weeks.
Adverse outcomes occurred in 1,903 women, including 178 cases of both SGA and hypertensive disorders, 8 with SGA plus stillbirth, 3 with hypertensive disorders plus stillbirth, and 2 cases with all three complications.
The researchers found no association between any adverse outcomes and sleep position either at the first visit in early pregnancy (adjusted odds ratio, 1.00; 95% confidence interval, 0.89-1.14) or the third visit in midpregnancy (aOR, 0.99; 95% CI, 0.89-1.11). Propensity score matching to adjust non-left lateral positioning to the composite outcome also showed no association.
In midpregnancy, there was an association between non-left lateral sleeping and reduced risk of stillbirth (aOR, 0.27; 95% CI, 0.09-0.75). “This observation is likely spurious owing to small numbers of stillbirths, Dr. Silver and associates said.
A post hoc analysis indicated that the study was sufficiently powered to detect clinically meaningful risks; ORs of 1.2 for hypertensive disorders, 1.23 for SGA, 2.4 for stillbirth, and 1.2 for the composite outcome.
Let sleeping mothers lie
Pregnant women have enough on their minds. They shouldn’t have to worry about sleep position as well, according to Nathan Fox, MD, professor of obstetrics, gynecology, and reproductive science at Icahn School of Medicine at Mount Sinai, New York, and Emily Oster, PhD, economist at Brown University, Providence, R.I., who wrote an accompanying editorial.
It may seem harmless to direct women to sleep on their left side even if it has no benefit, but restricting a woman’s sleep options may leave her less well rested at a time when she is about to enter a period of sleep deprivation, as well as contribute to general discomfort, in their opinion.
Also, in the rare cases of a bad outcome, advice based on limited or poor quality evidence contributes to “devastating and unwarranted feelings of responsibility and guilt, and this harm to women already suffering from sadness and despair must not be minimized,” they said.
The study received funding from the Eunice Kennedy Shriver National Institute of Child Health and Human Development and grants from multiple universities. One author received research funding from Kyndermed through her institution. Another receives royalties from UpToDate.com. Dr. Fox and Dr. Oster have no relevant financial disclosures.
SOURCES: Silver RM et al. Obstet Gynecol. 2019. doi: 10.1097/AOG.0000000000003458; Fox N and Oster E. Obstet. Gynecol. 2019 Oct. doi: 10.1097/AOG.0000000000003466