Pregnant women can lower the risk of stillbirth by sleeping on their side and NOT on their back, according to an international meta-analysis. The finding has been taken up as part of official National Health Service (NHS) guidance.
Dr Tomasina Stacey is reader of midwifery practice at the University of Huddersfield. She carried out her doctoral research while based at Auckland University in New Zealand, investigating whether sleeping position was a factor in stillbirth. She concluded that the small proportion of pregnant women who sleep on their backs did run a higher risk, because the weight of the uterus can reduce blood flow to the baby.
It was the first study to report maternal sleep-related practices as risk factors for stillbirth. It triggered further research, culminating in a large-scale international project that gathered data from New Zealand, the UK, Australia and the US.
This study included 851 bereaved mothers and 2,257 women with ongoing pregnancy. The chief finding is that going to sleep lying on the back from 28 weeks of pregnancy increased the risk of stillbirth by 2.6 times. This heightened risk occurred regardless of the other known risk factors for stillbirth.
The UK charity Tommy's, which funds research into miscarriage, stillbirth and premature birth, has included Stacey's findings about sleep position in its advice to pregnant women. And now the NHS has incorporated them in its Saving Babies' Lives care bundle – a dossier of advice issued as part of a push to halve the rate of stillbirths in the UK. The care bundle states: "In later pregnancy (after 28 weeks), it is safer to go to sleep on your side than on your back." It advises practitioners to "encourage women to settle on their side when they go to sleep or have a day-time nap, rather than on their back. A woman who wakes up on her back shouldn't worry, but should settle to sleep again her side."
Sleeping position remains an important strand of Stacey's research. It originated when she and a team at the University of Auckland – including her PhD supervisor Professor Lesley McCowan – were investigating the relatively high rates of stillbirth in New Zealand.
"We decided to look at a range of modifiable risk factors and this was one of them," said Stacey. "The next phase is to ensure that there is consistent advice from healthcare professionals and we will be looking to see if there are ways of helping to support women to sleep in the side position.
"Only a small proportion of women will be affected," continued Stacey. "But the studies that we did following the first findings suggested that women were quite happy to change their going to sleep position if it was better for their babies."
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 < 0.0001) compared with left side. Right side had similar odds to left (aOR 1.04, 95% CI 0.83–1.31, p = 0.75). There were no significant interactions between supine going-to-sleep position and assessed indicators of fetal vulnerability, including small-for-gestational-age infants (p = 0.32), maternal obesity (p = 0.08), and smoking (p = 0.86). The population attributable risk for supine going-to-sleep position was 5.8% (3.2–9.2).
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.
Robin S Cronin, Minglan Li, John M.D. Thompson, Adrienne Gordon, Camille H Raynes-Greenow, Alexander EP Heazell, Tomasina Stacey, Vicki M Culling, Victoria Bowring, Ngaire H Anderson, Louise M O'Brien, Edwin A Mitchell, Lisa M Askie, Lesley ME McCowan