Lying on your back while pregnant could increase the risk of stillbirth

Pregnant women who lie on their backs in the third trimester may be increasing the risk of stillbirth, according to a study published in The Journal of Physiology.

Researchers at the University of Auckland have found that lying face up while pregnant can change the baby’s heart rate and activity state which suggests that the fetus adapts by reducing its oxygen consumption. This finding may explain the increased risk of stillbirth in the supine (lying upwards) position.

Stillbirths are a common occurrence, with around 1 in 227 births in the UK ending in stillbirth1. Recent studies have shown that maternal position is important for the baby’s health, but it was unclear as to how this can affect the wellbeing of the fetus. This research reports that lying on your back can add stress and may reduce oxygen provided to the fetus, increasing the risk of stillbirth.

The researchers monitored the fetal and maternal heart rate for 29 healthy pregnant women in the third trimester while changing and maintaining maternal positions for 30 minutes at a time. The ‘fetal behavioural state’, a measure of fetal health, was recorded for each maternal position. Each woman was followed until delivery and all babies were born in a healthy condition.

Peter Stone, Professor of Maternal Fetal medicine at the University of Auckland and lead investigator of the study explained, “Our controlled study found that lying on your back can add extra stress to the baby, contributing to the risk of stillbirth. The risk is likely to be increased further in women with underlying conditions.”’

He added, “We have only looked at the effect of maternal positions for a short period of time while the mother is awake. Further research is needed to see the effect of staying in certain maternal sleeping positions overnight.”


 Image showing experimental set up

Image showing Experimental set up. Credit: Professor Peter Stone


Notes to Editors

  1. Link to source:
  2. Full paper title: Effect of maternal position on fetal behavioural state and heart rate variability in healthy late gestation pregnancy
  3. The Journal of Physiology publishes advances in physiology that increase our understanding of how our bodies function in health and disease.
  4. The Physiological Society brings together over 3,500 scientists from over 60 countries. The Society promotes physiology with the public and parliament alike. It supports physiologists by organizing world-class conferences and offering grants for research and also publishes the latest developments in the field in its three leading scientific journals, The Journal of Physiology, Experimental Physiology and Physiological Reports.



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Corresponding author

Professor Peter Stone

Department of Obstetrics and Gynaecology

The University of Auckland