Women who sleep on their left side on their final night of pregnancy could halve the risk of their baby being stillborn compared to women who do not, a new study has found.
Sleeping on the left allows free circulation through a large blood vessel that runs along the right hand side of the spine, maximising blood flow to the baby.
A new study conducted by researchers at the University of Auckland in New Zealand found that the absolute risk of late stillbirth for women who went to sleep on their left was 1.96 per 1,000.
The risk doubled to 3.93 per 1,000 for those who slept in any other position (such as on the right side or on the back).
“Other studies have suggested that the left side is optimal for some women in late pregnancy but this is the first time that an association between maternal sleep position and stillbirth has been investigated,” said lead researcher, Tomasina Stacey, a PhD student from the University of Auckland.
The study, which was published in the journal BMJ, involved interviews of 155 women in Auckland who had a stillborn baby between 2006 and 2009 when they were at least 28 weeks pregnant. A control group of 310 women with continuing pregnancies was also interviewed.
The women were asked about sleep position on the final night of pregnancy, as well as in the final week and final month. They also answered questions on snoring, napping during the day and how often they got up to urinate during the night.
After factoring in background risks such as smoking habit, weight, socio-economic status and age, the researchers found that snoring and feeling sleepy during the day did not impact on the risk of stillbirth.
Sleeping during the day and for longer periods during the night were linked to stillbirth, however.
Getting up during the night to urinate just once or less was also linked to late stillbirth, the study found.
It is thought that rising during the night may help raise blood pressure in women with naturally low blood pressure, thereby ensuring enough blood gets to the baby, said Dr Jane Warland, a midwife and expert in stillbirth from the University of South Australia.
“[These] findings make perfect sense physiologically,” said Dr Warland, who was not involved in the study.
It is common knowledge in the U.S. that women in the late stages of pregnancy should sleep on their left side but in other countries, such as New Zealand, that advice is not always given, she said.
“So this research has given us evidence for providing that advice for women across the globe.”
Dr Warland, who usually advises pregnant women to start left side-sleeping from at least 28 weeks onward, said around 1 in 140 babies are stillborn in Australia.
“If a pregnant woman has a 1 in 140 risk of stillbirth and by left sleeping you could lower that risk to 1 in 280, you’d take those new odds,” she said, but added that further research into the potential link should be done.
Dr Alexander Heazell from the University of Manchester School of Medicine in Britain also said the issue needed further investigation.
“There are several weaknesses in the study, including the fact that mothers were asked to recall their sleeping position 25 days after experiencing a stillbirth,” he said.
BMJ published an editorial alongside Ms Stacey’s research that argued that the results should be treated with caution.
“Compromised babies may have reduced movements in the days leading up to the death. Hence, rather than being a cause of stillbirth, the associations between longer sleep and not rising during the night in the week before stillbirth may reflect absent or reduced fetal movements, as a consequence of the baby’s death,” said the editorial, which was written by Lucy Chappell from the King’s College in London and Professor Gordon Smith from the University of Cambridge in the U.K.
“A forceful campaign urging pregnant women to sleep on their left side is not yet warranted. Further research is needed before the link between maternal sleep position and risk of stillbirth can be regarded as strongly supported.”
Ms Stacey, the lead researcher in the study, said she agreed.
“This is a novel finding and urgently needs confirming in other studies before any campaign is instigated,” she said.
“However, stillbirth is a far too common and tragic outcome of pregnancy and any new insights that may be able to reduce the incidence of stillbirth should be welcomed. This should be seen as a starting point for future study.”