Public Release: 

Sleep on your side, not your back in late pregnancy

The Physiological Society

A pregnant mother sleeping on her back during late pregnancy may cause problems for the fetus, according to new research published in The Journal of Physiology. This is the first study to monitor unborn babies overnight and at the same time record the mother's position during sleep.

The sleep position of women in late pregnancy has been shown to be related to an increased risk of late stillbirth (after 28 weeks gestation).

Researchers at the University of Auckland investigated sleep position of pregnant women by setting up an infrared video camera to record their position as they slept. They also continuous recorded the heart rate of the women and fetus overnight using an ECG device.

When the mother slept on her back, the fetus was less active. Fetal activity is one measure of its wellbeing. Fetuses were only in an active state when the mother was on her left or right side. When the mother changed position during sleep, for example from her left side to sleeping on her back, the baby quickly changed activity state and became quiet or still.

This research involved 30 pregnant women at 34-38 weeks gestation and all of them were healthy with healthy babies. The researchers are now investigating pregnancies where the fetus is not growing properly or the mother has reported decreased fetal movements, as both situations have been associated with an increased risk of stillbirth.

Peter Stone, one of the lead investigators on the study said, 'In the situation where the baby may not be healthy, such as those with poor growth, the baby may not tolerate the effect of maternal back sleeping. We are suggesting that there is now sufficient evidence to recommend mothers avoid sleeping on their back in late pregnancy, not only because of the epidemiological data but also because we have shown it has a clear effect on the baby.'

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