An Individual Participant Data Meta-analysis of Maternal Going-to-Sleep Position, Interactions with Fetal Vulnerability, and the Risk of Late Stillbirth

Abstract Background Maternal supine going-to-sleep position has been associated with increased risk of late stillbirth (≥ 28 weeks), but it is unknown if the risk differs between right and left side, and if some pregnancies are more vulnerable. Methods Systematic searches were undertaken for an individual-level participant data (IPD) meta-analysis of case–control studies, prospective cohort studies and randomised trials undertaken up until 26 Jan, 2018, that reported data on maternal going-to-sleep position and stillbirth. Participant inclusion criteria included gestation ≥ 28 weeks', non-anomalous, singleton pregnancies. The primary outcome was stillbirth. A one-stage approach stratified by study and site was used for the meta-analysis. The interaction between supine going-to-sleep position and fetal vulnerability was assessed by bi-variable regression. The multivariable model was adjusted for a priori confounders. Registration number: PROSPERO, CRD42017047703. Findings Six case–control studies were identified, with data obtained from five (cases, n = 851; controls, n = 2257). No data was provided by a sixth study (cases, n = 100; controls, n = 200). Supine going-to-sleep position was associated with increased odds of late stillbirth (adjusted odds ratio [aOR] 2.63, 95% CI 1.72–4.04, p  Interpretation This IPD meta-analysis confirms that supine going-to-sleep position is independently associated with late stillbirth. Going-to-sleep on left or right side appears equally safe. No significant interactions with our assessed indicators of fetal vulnerability were identified, therefore, supine going-to-sleep position can be considered a contributing factor for late stillbirth in all pregnancies. This finding could reduce late stillbirth by 5.8% if every pregnant woman ≥ 28 weeks' gestation settled to sleep on her side.