"New warning to pregnant women: Do not sleep on your back in the last trimester as it could cause stillbirth, claim experts," the Mail Online reports.
This rather overdramatic headline stems from a new study that investigated the effects of mothers' sleep positions on baby behaviour in 29 women in the final weeks of pregnancy.
Compared with when mothers slept on their left side, which was most common, babies were slightly more likely to be active and awake when women slept on their right side, and slightly more likely to be quietly asleep when women slept on their back.
But the differences in the babies' activity patterns were very small.
Changes in maternal position and a baby's activity pattern naturally altered the baby's heart rate pattern, but all the babies were born completely healthy.
On its own, this research doesn't provide any evidence that the position a mother sleeps in may harm her baby.
But previous research has suggested that sleeping on your back when you're pregnant may increase the risk of stillbirth, as it compresses the mother's major blood vessels and alters the baby's heart rate.
For this reason, the study's authors suggest women avoid sleeping on their backs in the last trimester of pregnancy.
The study was carried out by researchers from the University of Auckland in New Zealand.
Joint funding was received from the children's charity Cure Kids and the University of Auckland.
The study has been peer-reviewed and accepted for publication in The Journal of Physiology, but hasn't been formally published yet.
It's available to read free online as an accepted article, but there may be some changes in the production of the final draft.
Both the Mail Online and the Daily Mirror talk about an increase in the risk of stillbirths from a pregnant woman sleeping on her back.
The researchers didn't investigate this, and all the babies involved in this study were born healthy.
The main body of the media articles did, however, provide a more accurate representation of the findings.
This observational study aimed to investigate the effects of pregnant women's sleep positions on foetal behaviour late in the third trimester.
The third trimester starts from 29 weeks and continues to the end of pregnancy.
The researchers wanted to assess the effects in as natural a setting as possible. Women wore foetal monitors while they slept at home and weren't advised what position to sleep in.
Observational studies are useful for testing the link between a possible exposure and outcome – in this case, the mother's sleep position and foetal behaviour – but can't confirm cause and effect.
Although a randomised controlled trial (RCT) would be the most ideal way to test an association, it wouldn't be ethical to make pregnant women sleep in positions that may risk harming their babies.
The study recruited 29 healthy pregnant women carrying a single foetus who were late into their third trimester (36 to 38 weeks).
All women were told to sleep as they would normally, and the researchers set up recording equipment to study the participants in their own homes.
Video footage was collected to determine maternal sleeping position.
The onset of sleep was defined as the first three minutes during which there were no movements.
Position changes were counted as positions that were assumed for longer than three minutes.
Sleep positions through the night were categorised as:
A continuous foetal echocardiogram (ECG) was used to record maternal and foetal heart rate.
Mean foetal heart rate was assessed for every minute from when the mother fell asleep until she woke up. Consistent states were defined upon duration of three minutes.
Foetal behavioural states were determined using the following:
Researchers analysed the relationship between maternal position and foetal state.
The average maternal sleep duration was approximately eight hours. Sleeping on the left side was the dominant position in the majority of women.
Compared with the mother sleeping on her left side:
All babies were healthy at their six-week postnatal check-up.
The researchers said: "Our results have shown that time of night significantly influenced the likelihood of the foetus being in a particular state, with 4F being more likely in the early part of the night and 1F less likely then and more likely later after sleep onset.
"This may be due in part to the maternal position effects where position change, most often from non-supine to supine sleep, occurred after the period of most stable sleep.
"It was also found that the effects of foetal state on measures of foetal heart rate variability were modified by maternal position, likely mediated through autonomic nervous system activity.
"This further supports the concept that maternal position is an important modulator of circadian effects on foetal heart rate."
This observational study suggests a mother's sleep position may influence their baby's activity in late pregnancy.
Most mothers sleep on their left side, but babies were found to be slightly more likely to be actively awake if women slept on their right side.
If they slept on their backs, babies were slightly more likely to be quietly asleep.
These are interesting findings, but there are a few points to note:
Some organisations, such as the American Pregnancy Association, recommend pregnant women sleep on their left side as this will "increase the amount of blood and nutrients that reach the placenta".