Twenty years after doctors discovered that placing babies to sleep on their backs halved the rate of cot deaths, new research suggests pregnant women who sleep on their left side may halve the rate of stillbirths.

Researchers who surveyed 150 women in New Zealand who had stillbirths and compared them with 300 women who had normal births found the rate was 1.96 per 1,000 births for those who slept on their left but rose to 3.93 per 1,000 for those who slept on their right side or back. The findings are published in the British Medical Journal. Experts stressed the risk was low and the findings preliminary.

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.