Long periods of undisturbed sleep during pregnancy may be linked to late-term stillbirth (on or after 28 weeks of pregnancy), according to a new study published in the journal Birth.

Michigan Medicine researchers analyzed online surveys involving 153 women who had experienced a late stillbirth within the previous month as well as 480 women in their third-trimester of pregnancy or who had recently delivered a live born baby during the same period.

The findings suggest a link between lengthy periods of undisturbed maternal sleep (more than nine hours per night) and stillbirths that were independent of other risk factors. But researchers caution that more research is needed to better understand the relationship and what it means for pregnant women.

“Pregnant women often report waking up and getting up in the middle of the night,” said lead author Louise O’Brien, Ph.D., M.S., a University of Michigan researcher in the Division of Sleep Medicine, Department of Neurology and the Department of Obstetrics and Gynecology at Michigan Medicine.

“While multiple awakenings during the night may concern some women, in the context of stillbirth it appears to be protective.”

O’Brien said more research is needed to investigate what may be driving the relationship between maternal sleep and stillbirths, with particular focus on how the autonomic nervous system — the control system that regulates bodily function — and the hormonal system are regulated during sleep in late pregnancy.

She noted that blood pressure hits a low point during sleep, but when a person wakes up, there is a surge in the nervous system activity that causes transient increases in blood pressure.

It’s possible that these brief boosts in blood pressure are able to prevent long periods of relatively low pressure, O’Brien said. This is important, since low blood pressure has been associated with fetal growth problems, preterm birth, and stillbirth.

O’Brien also emphasizes that “pregnant women should not be waking themselves up at night.” Very disruptive sleep has also been linked to poor pregnancy outcomes, including growth restriction and preterm growth.

Although research has shown that very disrupted sleep and clinical sleep disorders are associated with poor pregnancy outcomes, few studies have looked at the opposite end of the spectrum, such as long periods of undisturbed sleep, said O’Brien.

“Our findings add to research indicating that maternal sleep plays a role in fetal wellbeing,” she said. “Studies aiming to reduce stillbirths should consider maternal sleep as this is a potentially modifiable risk factor. Understanding the role of maternal sleep may help us identify interventions that would put us in a better position to advise women.”

About 1 in 160 pregnancies in the U.S. is a stillbirth, with about 24,000 babies stillborn in the country every year — 10 times as many deaths that occur from Sudden Infant Death Syndrome (SIDS). About half of all stillbirths happen after 28 weeks of pregnancy and many remain unexplained.

And while rates are even worse in low income countries, the stillbirth rate in the U.S. is still higher than in many other Western countries.

Smoking, advanced maternal age, diabetes, obesity and drug abuse are among well-established risk factors for stillbirths. Maternal sleep practices, however, cover a relatively new area of research.

Source: Michigan Medicine, University of Michigan