*This story contains information which some readers may find distressing

It can be difficult to sleep while pregnant. Any number of issues can interrupt sleep, including the frequent need to urinate, back pain, abdominal discomfort and shortness of breath, among others.

Moreover, disruptive sleep during pregnancy can be risky for the foetus, contributing to curbing growth. But a recent study suggests that excessive, undisturbed sleep may be a problem, too.

Sleeping continuously for nine or more hours may be related to the danger of late stillbirth, that is, the loss or death of a baby before or during delivery.

Advertisement

"There's been a lot of public attention paid to sleep deprivation and its impact on health, but not as much to lengthy - perhaps too much - sleep, especially when it comes to pregnancy," said Louise O'Brien, research associate professor in the neurology sleep disorders center and in obstetrics and gynaecology at the University of Michigan. "Women often worry when they wake up several times during the night when they are pregnant, but it may be protective in this case."

O'Brien and her colleagues analyzed online surveys from 153 women who had experienced a late stillbirth (on or after 28 weeks of pregnancy) during the month previous to answering the questionnaire and 480 women with an ongoing third-trimester pregnancy or who had recently delivered a live born baby during the same period. The findings, recently published in the journal Birth, suggest a connection between long periods of undisturbed maternal sleep and stillbirth, independent of other risk factors.

Stillbirth affects about 1 per cent of all pregnancies, or about 24,000 annually in the United States, many of them unexplained, according to the Centers for Disease Control and Prevention.

O'Brien said that both the women with stillborn babies and the women with live-born babies reported a similar proportion of long sleep before they were pregnant, which was 10 per cent in both groups.

But nearly 30 per cent of those who had stillbirths reported long sleep in the last month of pregnancy compared with only 16 per cent of women with live-born babies.

"Given that a similar proportion of women in the stillbirth and live-birth group were long sleepers before pregnancy, but during pregnancy the stillbirth group had a significant increase in the proportion of women having long sleep, it would appear that it could be the change in sleep duration during pregnancy that is important," she said. "Being a lifelong long sleeper versus a pregnancy-associated long sleeper could be the difference."

She said further research was necessary, in particular studying how the autonomic nervous system, which regulates body functions, and the hormonal system, behave during sleep in late pregnancy.

Blood pressure reaches its lowest point during sleep but surges upon awakening, causing a brief, temporary increase. Photo / Getty Images
Blood pressure reaches its lowest point during sleep but surges upon awakening, causing a brief, temporary increase. Photo / Getty Images

She pointed out that blood pressure reaches its lowest point during sleep but surges upon awakening, causing a brief, temporary increase. These short-lived rises in blood pressure may prevent extended periods of low blood pressure, which has been linked to fetal growth problems, preterm birth and stillbirth, she said.

Advertisement

"Speculation that less awakenings in the mothers with stillborn babies could have resulted in fewer episodes of blood pressure elevation which could have been harmful to the foetus is intriguing," said Shawn Youngstedt, a sleep scientist at Arizona State University and the Phoenix VA Health Care System, who was not involved in the study. "Generally, blood pressure 'dipping' at night is thought to be healthy, but they have advanced a compelling argument that prolonged blood pressure declines during sleep might be harmful to the foetus. Interestingly, the higher prevalence of hypertension in the control women, compared with the cases, supports their argument."

Furthermore, "the cases had a significantly higher prevalence of diabetes, which might partly explain the results," he said. "Also, the authors raise a good point that depression and anxiety, which were not measured, might have contributed."

But Neomi Shah, associate professor of medicine, pulmonary, critical care and sleep medicine at Mount Sinai's Icahn School of Medicine, who also was not involved in the research, noted its limitations, in particular that it suggests an association between long uninterrupted sleep and stillbirth, but doesn't establish it as the cause.

Also, the research asks participants to recall specific behaviours, a methodology that can be problematic, Shah said.

"Cases are more likely to incorrectly recall sleep duration than controls and may overestimate their sleep duration thereby demonstrating an association with stillbirth when in reality it may not truly exist," Shah said. "The association of long sleep duration and stillbirth needs to be confirmed in a true experimental study design in order for us to target it as a potentially modifiable risk factor for stillbirth."

The study acknowledged the potential for "recall bias," but pointed out that "care was taken to minimise recall bias by limiting the study to women who had delivered a stillborn baby within the previous month, when events can be recalled."

Smoking, advanced maternal age, diabetes, obesity and drug abuse are among well-established risk factors for stillbirths. Maternal sleep practices have not been well-studied and represent a new research focus. O'Brien's study follows others that have examined links between mother's sleep habits and fetal condition, including studies suggesting an association between back-sleeping and stillbirths. While the current study asked about maternal sleep position, not enough women reported sleeping on their backs for any meaningful analysis, the researchers said.

O'Brien agreed on the need for further studies, especially if they prompt behaviour changes that could prevent stillbirth.

"Many risk factors for stillbirths are not able to be modified once pregnancy has begun," she said. "But we should be looking at every possible intervention that may prevent poor outcomes. Progress in reducing stillbirth deaths has been slow but stillbirth is an urgent global health issue that should be at the center of more research programs."

Because disruptive sleep also can lead to problems, O'Brien warned against pregnant women deliberately waking themselves up during the night until scientists know more.

"While extremes of sleep have been linked to health risks for mom and baby, getting up a few times in the night probably is nothing to worry about," she said.