Background: In individual studies maternal supine going-to-sleep position is reported to increase the risk of late stillbirth (>28 weeks’) 2.5 to 6 fold compared to left side position. We aimed to: 1) confirm the relationship between going-to-sleep position and late stillbirth risk and 2) test for interactions between sleep position and indicators of fetal vulnerability (small for gestational age [SGA], maternal smoking, and obesity).
Method: We searched publications identified by systematic bibliographic searches for studies that collected data on: women with late stillbirth and pregnant controls at similar gestation to cases, and late pregnancy sleep position with no sleep position intervention. One-step meta-analysis of individual participant data using mixed-effects models was performed.
Results: We identified data from four case-control studies (cases, n=713 late stillbirths; controls, n=1804). Pooled adjusted odds ratio [aOR] for supine going-to-sleep position compared to left side was 3.35 95% confidence interval [CI] 2.29 to 4.9, and for right side, 1.11 95% CI 0.89 to 1.38, compared to left side. There was no significant interaction between supine going-to-sleep position and maternal obesity (p=0.10), smoking (p=0.52), or SGA (0.21).
Conclusion: Our analysis found no difference between left or right side going-to-sleep position for women in the third trimester for fetal outcomes. As there was no interaction with measures of vulnerability, supine going-to-sleep position can be considered a risk factor for late stillbirth in all pregnancies.