Prolonged undisturbed sleep during pregnancy can be a cause of stillbirths

Washington: A new Michigan-led international study suggests that sleeping more than nine hours per night during pregnancy may be associated with late stillbirth.

Researchers analysed online surveys involving 153 women who had experienced a late stillbirth 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.

The findings, published in journal, Birth, suggest an association between lengthy periods of undisturbed maternal sleep and stillbirths that were independent of other risk factors. However, researchers caution that further research is needed to better comprehend the relationship and what it signifies for pregnant women. Speaking about the study, lead author of the study Louise O'Brien, from the University of Michigan said, "Pregnant women often report waking up and getting up in the middle of the night."

Brien is a researcher in the Division of Sleep Medicine, Department of Neurology and the Department of Obstetrics and Gynecology, at Michigan Medicine. The researcher said that further studies need to delve deeper into what may drive 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 notes that blood pressure reaches its lowest point during sleep but when someone is awakened, there is a surge in the nervous system activity that causes transient increases in blood pressure. It's possible that these brief increases in blood pressure are able to prevent long periods of relatively low pressure. This is important, O'Brien says, because low blood pressure has been linked with foetal growth problems, preterm birth, and stillbirth.

O'Brien also cautions that "pregnant women should not be waking themselves up at night." Very disruptive sleep has also been associated with poor pregnancy outcomes, including growth restriction and preterm growth. She further notes that while there already is evidence that disrupted sleep and clinical sleep disorders are associated with poor pregnancy outcomes, few studies looked at the opposite end of the spectrum, such as long periods of undisturbed sleep.

"Our findings add to research indicating that maternal sleep plays a role in foetal wellbeing," she says, adding, "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."

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 investigation. The new study follows other research looking at possible ties between maternal sleep and foetal well-being in recent years, including studies suggesting that women who report that they sleep on their backs have an increased risk of stillbirths. While the current study asked about maternal sleep position, not enough women reported sleeping on their backs for any meaningful analysis.