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Lying face up pregnant could increase risk of stillbirth

Researchers at the University of Auckland have found that pregnant women who lie on their backs in the third trimester, may be increasing their risk for stillbirth.


They are a common occurrence, with around 1 in 227 births in the UK ending in stillbirth. Recent studies have shown that maternal position is important for the baby's health, but it was unclear how position 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.

Researchers found lying face up while pregnant, can change the baby's heart rate and activity state — suggesting the fetus adapts by reducing its oxygen consumption. This may explain the increased risk of stillbirth in the supine (lying upwards) position.

Peter Stone, Professor of Maternal Fetal medicine at the University of Auckland and lead investigator of the study explained,"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."

Background: Fetal behavioural states (FBS) are measures of fetal wellbeing. In acute hypoxemia, the human fetus adapts to a lower oxygen consuming state with changes in the cardiotocograph and reduced fetal activity. Recent studies of late gestation stillbirth described the importance of sleep position in the risk of intrauterine death. We designed this study to assess the effects of different maternal positions on FBS in healthy late gestation pregnancies under controlled conditions. Method: Twenty nine healthy women had continuous fetal ECG recordings under standardized conditions in 4 randomly allocated positions, left lateral, right lateral, supine and semi-recumbent. Two blinded observers, assigned fetal states in 5 minute blocks. Measures of fetal heart rate variability were calculated from ECG beat to beat data. Results: Compared to state 2F, state 4F was less likely to occur when women were semi-recumbent (OR = 0.11 95%CI 0 02, 0. 55), and supine (OR = 0. 27 95%CI 0.07, 1.10).State 1F was more likely on the right (OR = 2.36 95%CI 1.11, 5.04) or supine (OR = 4.99 95%CI 2.41, 10.43) compared to the left. State change was more likely when the mother was semi-recumbent (OR = 2.17 95%CI 1.19, 3.95) or supine (OR = 2.67 95%CI 1.46, 4.85).There was a significant association of maternal position to mean fetal heart rate. The measures of variability (SDNN and RMSSD) were reduced in both semi-recumbent and supine positions. Conclusion: In healthy late gestation pregnancy, maternal position affects FBS and heart rate variability. These effects are likely fetal adaptations to positions which may produce a mild hypoxic stress.

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Nov 24, 2016   Fetal Timeline   Maternal Timeline   News   News Archive   

Study subject and baby being tested for this research.

Image Credit: Peter Stone PhD, University of Auckland, Australia


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