'Sufficient evidence' to recommend women avoid back-sleeping in late pregnancy
Expectant mothers should sleep on their side towards the end of pregnancy, experts have said after a new study highlighted the dangers of laying flat on their back
Researchers monitored both unborn babies and their mothers overnight to observe the effects of sleeping positions.
The study, published in The Journal of Physiology, found that women who sleep on their backs in late pregnancy may cause problems for the baby.
Previous studies have linked the position a mother sleeps in with an impact on the baby's risk of still birth - compared with sleeping on the left side, lying flat facing upwards was found to be linked to an increased risk of stillbirth.
In the new study, researchers decided to monitor the immediate impact sleeping positions have on a baby by measuring them overnight.
The research saw 29 healthy women who were 34 to 38 weeks pregnant given fetal electrocardiogram recordings overnight to monitor the heart activity.
Researchers from the University of Auckland also observed maternal sleeping positions using an infrared camera.
They found that when the mother slept on her back, the fetus was less active.
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, they found.
"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," said Peter Stone, one of the study's lead investigators.
"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."
Professor Alexander Heazell, spokesman for the Royal College of Obstetricians and Gynaecologists, said: "New research into stillbirth is welcome and this small study helps understand the potential link between a mother's sleeping position and stillbirth risk.
"Because we spend about one third of our lives asleep, more research is needed on sleep position in pregnancy and the effects it has on the baby and mother. We also need to know whether a mother can change her sleep position in late pregnancy and whether this reduces risk of stillbirth.
"It is also important to note that the risk of stillbirth after 28 weeks of pregnancy is about 1 in 300 pregnancies.
"It is important that women are not unnecessarily alarmed by the results of this small study of 29 women, all of whom had a healthy baby.
"This study was designed to explore the link between a mother going to sleep on her back and late stillbirth and has shown that babies' behaviours change.
"Presently, women should sleep in a position that is comfortable for them, and many find that sleeping on their side is the most comfortable. However, any woman with concerns should seek advice from their doctor or midwife."