Researchers found that among the 131 women they followed, those who averaged less than six hours of sleep per night during their ninth month of pregnancy were more than four times as likely to have a C-section as women who got more sleep. And women who had a tough time staying asleep for the night had a more than five-fold higher risk of needing a C-section.

In general, poor sleepers had a longer labor as well. On average, women who slept for less than six hours a night spent 29 hours in labor, compared with just under 18 hours for those who slept seven or more hours per night.

The findings, say the study authors, suggest that adequate, quality sleep during pregnancy is important in labor and delivery -- and that doctors should consider giving women a "prescription" for at least eight hours of sleep a night.

Drs. Kathryn A. Lee and Caryl L. Gay of the University of California, San Francisco, report the findings in the American Journal of Obstetrics and Gynecology.

To assess sleep quality and quantity in the study participants, the researchers had the women wear a motion-recording wrist device for 48 hours and keep a sleep log for the same two days, reporting the times they went to bed and woke up, and describing how well they slept. The women also completed a standard questionnaire on sleep problems.

The researchers found that women who averaged less than six hours of sleep on the two nights they were assessed had a C-section rate of nearly 37 percent, compared with just under 11 percent among women who got at least seven hours of sleep.

They found similar results when they looked at sleep disturbance, as measured by the wrist device. Women who showed severe sleep disruption -- meaning they were awake for more than one hour during the night after initially falling asleep -- had a C-section rate of 39 percent, versus 10 percent for women with little or no sleep disruption.

Fatigue, however, was not related to labor duration or type of delivery, nor was a woman's work status, although working women reported spending less time in bed. Other factors, such as maternal age and infant birth weight, did not explain the link between sleep and labor.

The reason for the relationship is unclear, and future studies should look at whether factors such as anxiety or stress hormone levels play a role, according to Lee and Gay.

For now, they conclude, doctors should discuss sleep quality with pregnant patients and "consider a specific prescription or recommendation of at least eight hours in bed at night."

They note that women in the study who suffered sleep disruptions typically did not try to compensate by spending more time in bed.

"Women with severe sleep disruption may need to increase their time in bed to assure a sufficient amount of sleep," the researchers write.

SOURCE: American Journal of Obstetrics and Gynecology, December 2004.