BACKGROUND AND PURPOSE:

• Supine sleeping position after 28 weeks is associated with reduced uterine blood flow and an increased risk of late stillbirth
  • Reduced uterine blood flow is also associated with fetal growth restriction
• Anderson et al. (JAMA Network Open, 2019) sought to determine if ‘going to sleep’ position during the third trimester is also associated with birth weight

METHODS:

• Subgroup analysis of previous meta-analysis
  • Women (from the control group) from the Collaborative Individual Participant Data Meta-analysis of Sleep and Stillbirth (CRIBSS) study population
  • CRIBSS study assessed sleep and stillbirth in New Zealand, Australia, and the U.K.
• Participants
  • Women with ongoing pregnancies ≥28w0d
  • Birth ≤42w6d
  • Sleep position data available up to 4 weeks before interview
• Groups
  • Supine going-to-sleep position
  • Nonsupine going-to-sleep position
• Data analysis
  • Adjusted mean difference (aMD) was calculated for birth weight between the two groups
  • Adjusted odds ratios (aORs) were determined for birth weight less than 50th and less than 10th centile between the groups
    • Adjusted for variables known to be associated with birth size
• Primary outcome
  • aMD in birth weight
• Secondary outcomes
  • Birth weight centiles
  • aORs for birth weight less than 50th and less than 10th centile (SGA)
  • Growth centiles used in this study
    • INTERGROWTH-21st centiles: Birth weight standard derived from a low-risk birth cohort | Adjusted for gestation at birth and infant sex
    • Customized centiles: Based on a fetal growth standard | Adjusted for gestation and infant sex as well as maternal height, weight, parity, and ethnicity

RESULTS:

• 1,760 women were included
  • 3.2% went to sleep supine during the previous 1 to 4 weeks prior to the interview
• Average birth weights, after adjustment, were reduced in the supine sleeping group (p=0.009)
  • Supine: 3410g
  • Nonsupine: 3554g
  • aMD: -144 g (95% CI, −253 to −36 g)
• Supine position was associated with a decreased mean INTERGROWTH-21st centile of
  • Supine: 48.5 centile
  • Nonsupine 58.6
  • aMD: −10.1 (95% CI, −17.1 to −3.1)
• Supine position was associated with a decreased mean customized centile
  • Supine: 40.7 centile
  • Nonsupine: 49.7
  • aMD: −9.0 (95% CI, −16.6 to −1.4)
• Supine position was associated with increased odds of birth weight less than the 50th customized centile (but not INTERGROWTH-21st centile)  
  • aOR 2.12 (95% CI, 1.20-3.76)
• Supine position was associated with an increase in odds of SGA by INTERGROWTH-21st centiles (but not customized centile)
  • aOR 3.23 (95% CI, 1.37-7.59) There was no significant difference in rates of
• There was no difference in risk for LGA
• Findings were similar for all nonsupine going-to-sleep positions, whether (1) left side (2) right side or (3) other

CONCLUSION:

• Among women who went to sleep supine in the last trimester, there was a significant association with reduced birth weight and birth weight centile
  • 2-fold increase in birth weight at <50th customized centile
  • 3-fold increase in odds of SGA by INTERGROWTH-21st centiles
• The authors state

Public health campaigns to encourage women to go to sleep lying on their side have potential to increase birth size

Learn More – Primary Sources:

Association of Supine Going-to-Sleep Position in Late Pregnancy With Reduced Birth Weight: A Secondary Analysis of an Individual Participant Data Meta-analysis

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