Most women experience sleep changes across the menstrual cycle. We applied
the ultra-short sleep-wake schedule to healthy females to compare their 24-
h sleep propensity rhythms in the follicular and luteal phases. The daytime
(09.00-16.30 h) subjective sleepiness and the number of slow wave sleep-co
ntaining nap trials increased in the luteal phase compared to the follicula
r phase, but the mean sleep propensity did not change. During the periods o
f 17.00-00.30h and 01.00-08.30h there were no differences between the two p
hases These results suggest that increased daytime sleepiness in the luteal
phase may be related to brain mechanisms controlling slow wave sleep.