Sleep and wakefulness in female rats during pregnancy

Sleep patterns were studied throughout pregnancy in female rats. The percentages of time spent in wakefulness, NREM sleep and REM sleep remained relatively constant from the beginning of pregnancy until shortly before delivery. For a period of approximately 15 hr prior to the onset of parturition there was an increased wakefulness and a decrease in both types of sleep. However, REM sleep decreased proportionally more than NREM sleep. During parturition the females were almost constantly awake allowing little time for NREM sleep and none for REM sleep. Soon after the end of parturition the amounts of NREM and REM sleep rose quickly to reach levels comparable to those obtained during pregnancy. The significance of these results is described in terms of the hormonal and nonhormonal events occurring at the time of parturition.