Pregnancy-associated sleep changes in the rat.

Sleep disorder during the course of pregnancy has been recently recognized in humans. However, the underlying mechanism of pregnancy-associated sleep disorder remains undetermined, and sleep changes even during normal pregnancy have not been fully understood. To describe the effects of pregnancy on sleep, sleep-wake patterns before and after fertile mating were compared in an animal model. Baseline recordings of sleep and brain temperature were made throughout a normal 4-day estrous cycle in female rats. After the rats became pregnant, the recordings continued across the entire pregnant period. Compared with baseline sleep before mating, both non-rapid eye movement sleep and rapid eye movement sleep increased significantly from the first night of pregnancy. Although rapid eye movement sleep returned to the baseline level from midpregnancy, nocturnal non-rapid eye movement sleep stayed enhanced during the entire pregnant period. Daytime sleep fluctuated toward the end of pregnancy. Brain temperature was elevated during the early period of pregnancy but did not correlate with enhanced sleep. The results suggest that physiological changes in different stages of pregnancy may contribute to the regulation of maternal sleep and temperature.