Association of Supine Going-to-Sleep Position in Late Pregnancy With Reduced Birth Weight

Abstract

IMPORTANCE Supine maternal position in the third trimester is associated with reduced uterine blood flow and increased risk of late stillbirth. As reduced uterine blood flow is also associated with fetal growth restriction, this study explored the association between the position in which pregnant women went to sleep and infant birth weight. OBJECTIVE To examine the association between supine position when going to sleep in women after 28 weeks of pregnancy and lower birth weight and birth weight centiles. DESIGN, SETTING, AND PARTICIPANTS Prespecified subgroup analysis using data from controls in an individual participant data meta-analysis of 4 case-control studies investigating sleep and stillbirth in New Zealand, Australia, and the United Kingdom. Participants were women with ongoing pregnancies at 28 weeks' gestation or more at interview. MAIN OUTCOMES AND MEASURES The primary outcome was adjusted mean difference (aMD) in birth weight. Secondary outcomes were birth weight centiles (INTERGROWTH-21st and customized) and adjusted odds ratios (aORs) for birth weight less than 50th and less than 10th centile (small for gestational age) for supine vs nonsupine going-to-sleep position in the last 1 to 4 weeks, adjusted for variables known to be associated with birth size. RESULTS Of 1760 women (mean [SD] age, 30.25 [5.46] years), 57 (3.2%) reported they usually went to sleep supine during the previous 1 to 4 weeks. Adjusted mean (SE) birth weight was 3410 (112) g among women who reported supine position and 3554 (98) g among women who reported nonsupine position (aMD, 144 g; 95% CI, −253 to −36 g; P = .009), representing an approximate 10-percentile reduction in adjusted mean INTERGROWTH-21st (48.5 vs 58.6; aMD, −10.1; 95% CI, −17.1 to −3.1) and customized (40.7 vs 49.7; aMD, −9.0; 95% CI, −16.6 to −1.4) centiles. There was a nonsignificant increase in birth weight at less than the 50th INTERGROWTH-21st centile (aOR, 1.90; 95% CI, 0.83-4.34) and a 2-fold increase in birth weight at less than the 50th customized centile (aOR, 2.12; 95% CI, 1.20-3.76). Going to sleep supine was associated with a 3-fold increase in small for gestational age birth weight by INTERGROWTH-21st standards (aOR, 3.23; 95% CI, 1.37-7.59) and a nonsignificant increase in small for gestational age birth weight customized standards (aOR, 1.63; 95% CI, 0.77-3.44). CONCLUSIONS AND RELEVANCE This study found that going to sleep in a supine position in late pregnancy was independently associated with reduced birth weight and birth weight centile. This novel association is biologically plausible and likely modifiable. Public health campaigns that (continued)

Mindfetalness to increase women’s awareness of fetal movements and pregnancy outcomes: a cluster‐randomised controlled trial including 39 865 women

“…We lack information but cannot exclude that some women may have embraced the idea of lying down of their left side frequently and that this lying position may have enhanced fetal growth. [35][36][37] A meta-analysis 38 showed an association between supine position and reduced birthweight. If women practising Mindfetalness more often lie on their side, this may explain the lower rate of babies born small-for-gestational-age in the Mindfetalness group.…”

Maternal sleep behaviours preceding fetal heart rate events on cardiotocography

“…Despite the women in this study spending a quarter of the night in the supine position, we were surprised to find that supine sleep position was not temporally associated with adverse FHR changes, for neither healthy nor complicated pregnancies. Relationships have been reported between self-reported supine 'sleep onset' during the later stages of pregnancy and fetal wellbeing, including reduced birthweight, fetal cerebral redistribution and stillbirth (Anderson et al 2019;Cronin et al 2019;Robertson et al 2020). There is biological plausibility for the supine position causing detrimental effects including aorto-caval compression resulting in decreased cardiac output (Humphries et al 2019) and impaired utero-placental blood flow (Jeffreys et al 2006).…”

A decrease in cesarean sections and labor inductions among Swedish women by awareness of fetal movements with the Mindfetalness method

“…Women who read the leaflet might have therefore adopted this position when going to sleep, rather than a supine position. Researchers have found an association between supine sleep position and reduced birthweight and even stillbirth [17,18].…”