Stillbirth

Epidemiological data suggests that one in four women sleep in a supine position at some point during the night [1]. Stillbirths affect between 1.7 to 8.8 per 1000 births in high-income countries [2] and multiple recent studies have identified supine sleep in late pregnancy as a novel, modifiable risk factor for stillbirth [1,2,3,4,5,6,7]. A UK study that compared maternal sleep practices between women who experienced a stillbirth (after ≥ 28 weeks gestation; n=291) and women who are currently pregnant (n=733); both with similar gestation, found that going to sleep in a supine position contributes to late stillbirth and population-attributable risk for supine going-to-sleep position was determined to be 3.7% [2]. A multicenter stillbirth case-control study conducted in New Zealand tested the hypothesis that supine going-to-sleep position would contribute to late stillbirth (≥28 weeks of gestation). 164 women who experienced late stillbirth and 569 randomly chosen women with ongoing pregnancies were asked to self-report their going-to-sleep position on the last night (the night before late stillbirth happened or for controls, the night before the interview). The study found that there was an increased late stillbirth risk of 3.7 fold for supine going-to-sleep position on the last night independent of other common risk factors (obesity, smoking, advanced maternal age, and small for gestational age) [3].

The link between supine sleep in late pregnancy and stillbirth can be biologically explained; sleeping in a supine position during late pregnancy causes the uterus to compress the inferior vena cava and the aorta which causes an 85% reduction in blood flow through the vena cava at its origin and approximately 30% reduction at the aortic bifurcation. This compression diverts the blood into the collateral venous circulation which results in a decrease in stroke volume by 11–25% and a decrease in cardiac output by 9–29%. This in turn leads to a reduction in uterine and placental perfusion and fetal oxygenation [4]. A study published in The Lancet concluded that 5.8% of stillbirths could be prevented if women in their late pregnancies slept in a lateral position rather than supine [4].

Sources

[1] N. Robertson, S. Okano, and S. Kumar, “Sleep in the supine position during pregnancy is associated with fetal cerebral redistribution,” J. Clin. Med., vol. 9, no. 6, p. 1773, 2020.

[2] A. Heazell et al., “Association between maternal sleep practices and late stillbirth - findings from a stillbirth case-control study,” BJOG, vol. 125, no. 2, pp. 254–262, 2018.

[3] L. M. E. McCowan et al., “Going to sleep in the supine position is a modifiable risk factor for late pregnancy stillbirth; Findings from the New Zealand multicentre stillbirth case-control study,” PLoS One, vol. 12, no. 6, p. e0179396, 2017.

[4] R. S. Cronin et al., “An individual participant data meta-analysis of maternal going-to-sleep position, interactions with fetal vulnerability, and the risk of late stillbirth,” EClinicalMedicine, vol. 10, pp. 49–57, 2019.

[5] T. Stacey, J. M. D. Thompson, E. A. Mitchell, A. J. Ekeroma, J. M. Zuccollo, and L. M. E. McCowan, “Association between maternal sleep practices and risk of late stillbirth: a case-control study,” BMJ, vol. 342, no. jun14 1, pp. d3403–d3403, 2011.

[6] J. T. Owusu et al., “Association of maternal sleep practices with pre-eclampsia, low birth weight, and stillbirth among Ghanaian women,” Int. J. Gynaecol. Obstet., vol. 121, no. 3, pp. 261–265, 2013.

[7] A. Gordon, C. Raynes-Greenow, D. Bond, J. Morris, W. Rawlinson, and H. Jeffery, “Sleep position, fetal growth restriction, and late-pregnancy stillbirth: the Sydney stillbirth study: The Sydney stillbirth study,” Obstet. Gynecol., vol. 125, no. 2, pp. 347–355, 2015.

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