Expecting? Sleep on your left -- just in case

Mothers who sleep on their backs or right-hand sides the night before giving birth are twice as likely to have a stillborn child compared with those who sleep on their left, according to a new study. Researchers found the risk of stillbirth for those sleeping on the left side was 1.96 per 1 000 births, and 3.93 per 1 000 births for any other position.

Tomasina Stacey, a midwifery lecturer at the University of Auckland, New Zealand, who led the study, cautioned pregnant women not to be overconcerned by the finding. “It was an observational study, not one that can show cause and effect—all it does is show an association.
It would be premature to jump up and down and say that everyone has got to sleep on their left. It’s a starting point for future research.

“Stillbirth is a much bigger problem than most people realise and many are unexplained,” said Stacey. “In the United Kingdom and New Zealand there has been very little change in the rate in the past 15 years.”

For the study, published in the British Medical Journal, she and her colleagues spoke to 155 women who had stillborn babies in Auckland between 2006 and 2009. They were asked about, among other things, their positions on going to sleep and waking up in the final weeks and month before the death of their babies. The researchers wanted to examine the effects of sleep disorders in pregnant women, such as sleep apnea or snoring, which could be a factor in stillbirths, because these conditions can reduce the amount of oxygen getting to the baby.

Instead, the study showed that sleep position on the night before birth was the decisive factor. Stacey said a possible explanation could be that when a woman does not sleep on her left side, the foetus could compress her inferior vena cava taking blood back to the heart. A reduced flow means less oxygen gets to the mother’s and baby’s other organs.

“If you’ve got a strong healthy baby, then the slightly reduced blood flow is fine; but if you’ve got a baby that is compromised in some other way, then maybe that reduction in blood flow can be the tipping point,” said Stacey. The left lateral position is known to be the optimal position for looking after a woman in labour and is associated with foetal wellbeing in labour, she said.

An accompanying editorial in the journal by Lucy Chappell of King’s College London says “any simple intervention that reduces the risk of stillbirth would be extremely welcome”, but states that the finding should be treated with caution.

Stacey said her advice to those women who found it uncomfortable to sleep on their left was “not to worry about it too much”. But, she said, at a population level, the associations between position and stillbirth might be important.

“We could make a difference to the stillbirth rate by encouraging people to sleep on their left.”—

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