A study published in the British Medical Journal (BMJ) last week (15th June) suggests that mums who sleep on their left side in late pregnancy are less likely to have a stillbirth than mums who sleep on their right side or on their back.

The study has received considerable attention in the media, drawing parallels with the ‘back to sleep’ campaign that had such an impact on cot deaths. From the perspective of many bereaved mums the reporting may have caused anxiety about their own baby’s death and made them wonder if their sleeping position was a factor. This statement aims to clarify what the study says, as well as reassure mums who slept on their backs or right side.

The study was carried out in New Zealand, questioning mums who’d had a stillbirth in late pregnancy about their sleep patterns, and comparing the answers with mums whose babies were born alive. This is the first time a study has looked at sleep in relation to stillbirth.

The researchers found an association between sleep position and the likelihood of a stillbirth: women who slept on their left side in late pregnancy had a reduced risk of a late stillbirth (after 28 weeks) compared to women who slept in any other position. 

However, though on the surface these findings sound persuasive, the true picture about a possible link is not at all clear.

Firstly it’s important to point out that the difference in the risk of stillbirth for different sleep positions was slight.

The overall risk of late gestation stillbirth is 3.09/1000 (which means 3.09 stillbirths for every 1000 live births); the risk of stillbirth for women who slept in positions other than on the left side was 3.93/1000. In other words, not sleeping on the left made little difference to the likelihood of having a stillborn baby.

The risk of stillbirth for women who reported sleeping on their left was around half the risk for other sleep positions, at 1.96/1000. But there are a number of reasons why this apparent decrease in risk must be treated with caution:

1.    The study does not show that sleeping on the right or on the back causes a stillbirth or even that sleep position definitely affects stillbirth, only that an association was observed. 

2.    The way the study was carried out means that the link the researchers observed might very well be due to chance rather than any actual link.

3.    There may well be bias in the study: for example women were interviewed some time after their baby’s death and might not have remembered accurately the details of their sleep patterns.

4.    There may be ‘reverse causation’ which means that rather than something about sleep position causing stillbirth, it might be the other way round i.e. the fact the baby had died may have influenced the mothers’ sleep position.

The researchers themselves emphasise that this study is only preliminary and needs to be repeated to see if the same findings are observed in another group of mums. Until the findings have been validated in further studies, they cannot be relied on as they may in future be found to be incorrect.

That message is echoed in the accompanying BMJ editorial which says, “No forceful campaign for pregnant women is warranted yet...further research is required before this link can be regarded as strongly supported."

For a full analysis of the study go to http://www.nhs.uk/news/2011/06June/Pages/mothers-sleeping-position-and-risk-of-stillbirth.aspx

In summary, the message for parents whose baby has died is:

Sadly we still don’t know why many stillborn babies die. Research is exploring lots of possible explanations to try and find better answers. The idea of there being a link between stillbirth and sleep position is an unusual one that has only been looked at by the researchers whose study appeared in the BMJ.

The link they found between stillbirth and left hand sleeping made only a small difference to overall stillbirth risk, and because of the way they carried out the study, it’s very possible that the link was due to chance or bias rather than due to any real causal connection. At the very least the study needs to be repeated before anyone can draw any conclusions about sleep position.

In other words there is no firm evidence to say left hand sleeping makes any difference at all to stillbirth, and mums should be reassured that this study does not show that their sleeping position was the cause of their baby’s death.

There is quite a strong feeling that this study should not have been published until more work has been done to find out if a link is there or not. Unfortunately there will be many bereaved mums wondering unnecessarily if they did something wrong.