Sleeping more than nine hours per night during pregnancy may be associated with late stillbirth, suggests a new study.

This is because blood pressure reaches its lowest point during sleep which has been linked with foetal growth problems, preterm birth, and stillbirth. The study, led by a team from the University of Michigan, explored how maternal sleep habits, including lengthy periods of sleep without waking more than once in the night, may be associated with foetal health independent of other risk factors.

Moreover, pregnant women often report waking up and getting up in the middle of the night. Very disruptive sleep has also been associated with poor pregnancy outcomes, including growth restriction and preterm growth. "Our findings add to research indicating that maternal sleep plays a role in foetal well being. Studies aiming to reduce stillbirths should consider maternal sleep as this is a potentially modifiable risk factor," said lead author Louise O'Brien, researcher at the varsity. "Understanding the role of maternal sleep may help us identify interventions that would put us in a better position to advise women," O'Brien added.

For the study, reported in the journal Birth, the team involved 153 women who had experienced a late stillbirth (on or after 28 weeks of pregnancy) within the previous month and 480 women with an ongoing third-trimester pregnancy or who had recently delivered a live born baby during the same period. Progress in reducing stillbirth deaths has been slow but stillbirth is an urgent global health issue that should be at the centre of more research programmes, the researchers noted.