The objective: to conduct a prospective analysis of the impact of cognitive behavioral therapy (CBT) and the level of endogenous melatonin in pregnant women with sleep disorders according to the Pittsburgh Sleep Quality Index (PSQI).Materials and methods. A randomized controlled trial was conducted in a group of 110 pregnant women with diagnosed sleep disorders. Sleep disorders were determined in the II and III trimesters of pregnancy using the PSQI questionnaire with additional questions for pregnant women.Study participants were randomly assigned to a main group (n=49) and a comparison group (n=61). To improve sleep in the main group 10 sessions of CBT were conducted over 10 weeks, and in the comparison group sleep hygiene psychoeducation was performed as generally recommended measures. In all study participant, the level of endogenous melatonin was determined indirectly by its metabolite – 6-sulfatoxymelatonin (6-SOM) in the urine.The condition of pregnant women in both groups was assessed for the effect of CBT at the beginning and after the end of treatment (week 10) using the PSQI questionnaire with additional questions for pregnant women and the level of 6-COM in urine. The impact of sleep disorders and CBT on the frequency of perinatal outcomes was also evaluated.Results. Pregnant women with sleep disorders had a reduced level of 6-SOM in urine. After the CBT sessions in the main group the PSQI indicators significantly decreased, and the level of 6-COM in the urine increased dynamically compared to the comparison group (p<0.05), in which the results were not statistically different from the data before the start of therapy (p>0.05).Conclusions. Conducting CBT sessions reliably improves the quality of sleep in pregnant women, which is consistent with the normalization of the level of 6-SOM in urine, and reliably reduces the number of perinatal complications. The PSQI questionnaire and determination of the level of 6-COM in urine can be recommended as subjective and objective tools for assessing the quality of sleep in pregnant women.