Restless sleep reported by many women in the final trimester of pregnancy may be a physiological mechanism protecting the fetus from the risk of late stillbirth, international researchers say.

The unexpected finding emerged from a meta-analysis of five case-control studies in which 851 women who had a stillbirth at or after 28 weeks’ gestation, or intrapartum, were compared with 2257 other pregnant women who went on to have a live birth.

The researchers, including authors of the Sydney Stillbirth Study published in 2015, examined factors to do with sleep reported by the women in questionnaires about the month before their stillbirth and, for the control group, for a matching time period during their pregnancy.

While 45% of women who went on to have a live birth reported having restless sleep greater than average in the previous month, just 38% of those who had a late stillbirth said they had more restless sleep than usual in the month prior to stillbirth.