Mothers-to-be who spend too much or too little time catching zzzz's early in pregnancy are more likely to have higher blood pressure as childbirth approaches. The result can lead to grave complications for both mother and baby, a new study suggests.

Researchers from the University of Washington observed that blood pressure rose by about 4 points in third-trimester women who reported sleeping less than six hours or more than 10 hours per night in early pregnancy.

The study was published today (Oct. 1) in the journal Sleep.

"Those small increases in average blood pressure translate to a clinically significant risk for preeclampsia," a dangerous condition involving pregnancy-induced blood pressure spikes and excess protein in the urine, said study researcher Michelle A. Williams, professor of epidemiology at the university's School of Public Health.

"The worst cases can lead to very horrible outcomes in mother and baby," she said, including retinal detachment, seizures or stroke in women, low birth weight or breathing difficulties in newborns, or death for either. The study also indicated that very short sleepers — those who slept less than five hours per night during early pregnancy — were 10 times more likely to develop preeclampsia than those who slept six hours or more.

"It's only a few points, but I do think it's significant. It's just the tip of the iceberg," said Dr. William Kohler, medical director of the Florida Sleep Institute and a spokesperson for the American Academy of Sleep Medicine, who was not involved with the study.

Sleep puzzle

Previous studies have established that high blood pressure is more prevalent among people of all ages who sleep less than six hours per night, and the same mechanism is likely to be at work in pregnant women, Williams told MyHealthNewsDaily.

Because blood pressure is known to dip by an average of 10 percent to 20 percent during sleep, short sleep durations may raise the average 24-hour blood pressure and heart rate, according to researchers. This may lead to structural changes that gradually raise blood pressure long-term.

But Williams said she and other researchers are puzzled about why longer sleep times during early pregnancy also produced small blood pressure surges similar to those seen in shorter sleep durations. They suspect, she said, that undiagnosed, underlying conditions such as sleep apnea, depression, or insulin resistance create the need for more sleep and may influence the findings.

The norm: 9 hours a night

More than 1,270 healthy pregnant women participated in the study, which relied on self-reported sleep durations given during interviews conducted when they were about 14 weeks pregnant. About 20 percent of the women reported sleep times of nine hours per night, which the researchers used as the norm.

About 55 percent of the pregnant women reported sleeping seven to eight hours, while 13 percent slept six hours or less, and 10 percent slept 10 hours or more.

Williams said her future research will focus on understanding why longer sleep durations lead to small rises in blood pressure.

"Moving forward, large-scale sleep studies should include pregnancy cohorts so that health-care providers and mothers-to-be can more fully appreciate the health risks of insufficient sleep," she said.

The research was supported by grants from the Eunice Kennedy Shriver Institute of Child Health and Human Development of the National Institutes of Health.

 This article was provided by MyHealthNewsDaily, a sister site to LiveScience.