Pregnant women who go to sleep on their backs in the final trimester deliver smaller babies than those who favour other sleeping positions, a New Zealand-led study shows.

In light of their findings, a public health campaign encouraging pregnant women to settle on their sides may have potential impacts on birth size, the researchers say.

“This study found that supine maternal going-to-sleep position is associated with reduced birth size in late pregnancy,” the authors wrote in JAMA Network Open.

In their study — analysing data from 1760 women at 28 weeks’ gestation or more from New Zealand, Australia and the UK — 57 (or 3.2%) reported that they had usually slept on their backs in the previous four weeks.