Women who sleep on their right side or back during late pregnancy could be at increased risk of stillbirth, research suggests.
Experts found a link between certain sleeping positions and the chance of late stillbirth (28 weeks or over) in a study of more than 450 women.
The overall risk of late stillbirth was small – just three per 1,000 births – but researchers said the findings needed “urgent confirmation” in other studies.
Some 155 women who had a late stillbirth were questioned about their lifestyles, and compared with 310 women who went on to have healthy pregnancies.
The women were questioned in the first few weeks after stillbirth and asked about things such as the positions they fell asleep and woke up in, whether they were sleepy during the day and whether they snored.
They were also asked how often they got up to go to the toilet during the night, and how often they did all of these things in the last month, week and night before their baby died. The research found that women who slept on their back or on their right side on the previous night before stillbirth were twice as likely to experience stillbirth compared with women who slept on their left side.
The absolute risk of late stillbirth for women who went to sleep on their left was 1.96 per 1,000 births but rose to 3.93 per 1,000 for women who slept in any other position.
The risk seemed to be slightly higher for women who went to sleep on their back.
Women who got up to go to the toilet once or less on the last night were also more than twice as likely to experience a late stillbirth as women who got up more frequently.
And those women who regularly slept during the day in the previous month were also more likely to experience a late stillbirth as those who did not.
No relation was found between snoring or daytime sleepiness and risk of late stillbirth, but sleeping for longer than average at night slightly increased the risk.
The findings held true even when factors such as age, smoking status, body mass index and social deprivation were taken into account.
Previous studies have found that a woman’s position in late pregnancy, either when resting or giving birth, can have an impact on cardiac output and delivery of oxygen to the foetus.
The womb seems to exert greater pressure on blood vessels when the mother lies on her back or her right compared with on her left, thereby decreasing blood flow.
Writing online in the British Medical Journal, the experts, who included professors, researchers and lecturers from the University of Auckland, called for further studies to test the findings.
They said: “If our findings are confirmed, promoting optimal sleep position in late pregnancy may have the potential to reduce the incidence of late stillbirth.”
In an accompanying editorial, Lucy Chappell, from King’s College London, said that, given the UK has one of the highest rates of stillbirth in the developed world, “any simple intervention that reduces the risk of stillbirth would be extremely welcome”.
However, she said the research needed to be interpreted with extreme caution and there may be several reasons for the findings.