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Objectively Measured Maternal Supine Sleep and Fetal Growth: A Prospective Cohort Study
Journal article   Open access   Peer reviewed

Objectively Measured Maternal Supine Sleep and Fetal Growth: A Prospective Cohort Study

Danielle L Wilson, Dwayne L Mann, Irene Szollosi, Leonie Callaway, Alka Kothari and Philip I Terrill
BJOG, Vol.Advanced access
13-Apr-2026
DOI: https://doi.org/10.1111/1471-0528.70246
PMID: 41978237
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BJOG - 2026 - Wilson - Objectively Measured Maternal Supine Sleep and Fetal Growth A Prospective Cohort Study1.55 MBDownloadView
Published Version (Advanced Access) Open Access CC BY V4.0

Abstract

night‐to‐night variability phenotype subjective posture back sleep onset pregnant
Objective To explore the relationship between different definitions of objectively measured supine sleep position during late pregnancy and customised birthweight centile, as a marker of fetal wellbeing. Design Prospective cohort study. Setting Australian public hospital antenatal clinic. Population Eighty-four pregnant women from 32–36 weeks of gestation. Methods Body position was measured in degrees of roll using a tri-axial accelerometer worn around the abdomen for seven sequential nights. Supine was defined as ‘broad supine’ (0° = fully supine to 45° left/right tilt), and ‘supine low-tilt’ (0°–15°). Two additional Risk Indices capturing risk proportional to duration spent in each degree of supine-to-lateral tilt were developed. Birthweights were converted into customised centiles using GROW software. Main Outcome Measures The primary outcome was customised birthweight centile. Secondary outcomes included birthweight, gestational age at delivery, and fetal growth trajectory. Results Across 556 nights of data, the median nightly duration of broad supine positioning was 65.9 [25.0, 125.7] minutes compared to only 9.1 [0.7, 24.4] minutes of supine low-tilt. There was no relationship between customised birthweight centile and time spent in broad supine (R2 = 0.0027, F(1,82) = 0.22, p = 0.64) or supine low-tilt (R2 = 0.0029, F(1,82) = 0.24, p = 0.63); nor with any supine risk index and customised birthweight centile, birthweight, gestational age at delivery, or fetal growth trajectory. Conclusion In this cohort, there was no evidence of an association between objectively measured supine sleep and customised birthweight centile. Yet to be identified mechanisms unrelated to fetal growth may be responsible for supine going-to-sleep position being a risk factor for late stillbirth. Further prospective investigation is needed to untangle cause and effect; however, given the low rate of stillbirth, such a study may not be feasible.

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