Melatonin and hormonal changes in disturbed sleep during late pregnancy.

Although sleep disturbance is commonly reported in pregnancy, there have been surprisingly few studies on the etiology of this condition. Since most hormones show circadian rhythmicity and maintain specific phase relationships with that of the sleep-wake cycle, it was of interest to establish whether sleep disturbances covaried with endocrine changes. This overnight study of pregnant women compared melatonin, cortisol, and prolactin secretion rhythms in six good sleepers and six poor sleepers. The groups were compared by ratios of the areas under the various hormonal curves. Significant differences in the cortisol/melatonin ratio were found between the poor sleeper group (lower values) and the good sleeper group (higher values). Nonsignificant trends, which might be expected to become significant with larger sample sizes, were found for decreased amplitude in the cortisol rhythm and increased amplitude in the melatonin rhythm in poor sleepers. The decreased amplitude of the cortisol rhythm in poor sleepers appeared to be due to a suppression of the early morning (0500-0800) rise. Prolactin levels were high and showed no rhythmicity in both groups. These differences may reflect changes in the circadian pacemaker system of poor sleepers, with increases in melatonin release being a response to counteract poor sleep.