Maternal Sleep Position and Adverse Pregnancy Outcomes: The NuMoM2b Prospective Cohort Study

Background: Maternal sleep position on the back or right side has been associated with adverse pregnancy outcomes, leading to recommendations to always sleep on the left side and maternal anxiety about sleep. However, available data are from case-control studies, which are subject to recall bias. Our objective was to examine the relationship between prospectively assessed sleep position and subsequent adverse pregnancy outcomes. Methods: This was a secondary analysis of a prospective observational multicenter cohort study of nulliparous women with singleton gestations. Participants prospectively completed in-depth sleep questionnaires between 6+0 and 13+6 week's gestation (V1) and 22+0 and 29+6 week's gestation (V3). At each visit, women were asked in what position they went to sleep last night and on average during the past week. A subset of women also underwent level 3 home sleep tests using the Embletta Gold device. The primary outcome was a composite of adverse pregnancy outcomes including stillbirth, small for gestational age fetus (SGA), and gestational hypertensive disorders. Results: 8,706 (of 10,038 total) women had data from at least one sleep questionnaire and for pregnancy outcomes, and they comprised the population for this analysis. There was no association between reported non-left lateral or supine sleep during the last week at V1 or V3 and the composite or any individual outcome, except for an apparent protective effect for stillbirth at V3. Women with objectively measured supine sleep position for > 50% of the time were no more likely than those in the supine position ≤ 50% of the time to have the composite adverse outcome. Conclusions: Going to sleep in the supine or right lateral position, as self reported prior to the development of pregnancy outcome and objectively assessed through 30 weeks gestation was not associated with an increased risk of stillbirth, SGA fetus or gestational hypertensive disorders. Trial Registration: clinicaltrials.gov (NCT01322529) Funding Statement: This study is supported by grant funding from the Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD): U10 HD063036, RTI International; U10 HD063072, Case Western Reserve University; U10 HD063047, Columbia University; U10 HD063037, Indiana University; U10 HD063041, University of Pittsburgh; U10 HD063020, Northwestern University; U10 HD063046, University of California Irvine; U10 HD063048, University of Pennsylvania; and U10 HD063053, University of Utah. In addition, support was provided by respective Clinical and Translational Science Institutes to Indiana University (UL1TR001108) and University of California Irvine (UL1TR000153). Declaration of Interests: No conflicts of interest to declare or report. Ethics Approval Statement: The study was approved by the Institutional Review Boards at each clinical site and the Data Coordinating Center, and all participants gave written informed consent.