Women in late pregnancy urged to sleep on their sides

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A pregnant mother sleeping on her back during late pregnancy may cause problems for the foetus, according to research. 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 foetus overnight using an ECG device.

When the mother slept on her back, the foetus was less active. Foetal activity is one measure of its wellbeing. Foetuses 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 foetal 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.’

Background: Fetal behavioural states (FBS) are measures of fetal wellbeing. Maternal position affects FBS with supine being associated with an increased likelihood of fetal quiescence consistent with the human fetus adapting to a lower oxygen consuming state. A number of studies now confirm the association of sleep position with risk of late intrauterine death. We designed this study to observe the effects of maternal sleep positions overnight in healthy late gestation pregnancy.
Method: Twenty nine healthy women had continuous fetal ECG recordings overnight. Two blinded observers, assigned fetal states in 5 minute blocks. Measures of fetal heart rate variability (FHRV) were calculated from ECG beat to beat data. Maternal position was determined from infrared video recording.
Results: Compared to state 2F (active sleep), 4F (active awake-high activity) occurred almost exclusively when the mother was in a left or right lateral position. State 1F (quiet sleep) was more common when mother was supine (OR 1.30, 95%CI, 1.11-1.52) and less common on maternal right side with the left being referent position (OR 0.81, 95%CI, 0.70-0.93). State 4F was more common between 2100 and 0100 than between 0100 and 0700 (OR 2 2.83, 95%CI, 2.32-3.47). In each fetal state, maternal position had significant effects on fetal heart rate (FHR) and measures of FHRV.
Conclusion: In healthy late gestation pregnancy, maternal sleep position affects FBS and heart rate variability. These effects are likely fetal adaptations to positions which may produce a mild hypoxic stress.

Peter R Stone, Wendy Burgess, Jordan McIntyre, Alistair J Gunn, Christopher A Lear, Laura Bennet, Edwin A Mitchell, John MD Thompson

The Physiological Society material
The Journal of Physiology abstract

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