premature infants
very low birth weight


Background. The sex-related differences of the urinary 6-sulfatoxymelatonin have not been studied in premature infants yet. The purpose of the work was to measure the daily urinary 6-sulfatoxymelatonin in premature infants with a very low birth weight.

Materials and Methods. Fifty premature infants (28 males and 22 females) with gestational age less than 33 weeks and body weight from 999 g to 1499 g were involved in the study. Urine 6-sulfatoxymelatonin was assessed using urine collection on the 1st day and on the 10th‒14th days of life.

Results. The level of urine 6-sulfatoxymelatonin on the 1st day of life showed a significant increase in its excretion in females compared to males. The median values in males were 202.0 (95% CI 77.1–390.9) pg/ml and in females 437.0 (279.6–501.0) pg/ml, p=0.0103. Its level on the 10th–14th days of life significantly decreased both in males 57.0 (95 % СІ 45,0–99.7) pg/ml, p=0.0028 and in females 90.0 (51.9–160.7) pg/ml, p=0.0021 without differences in sex-related distribution, p=0.3940.

Conclusions. The melatonin metabolite as urinary 6-sulfatoxymelatonin in premature infants with a very low birth weight demonstrates sex-related differences with significant increase in females compared to males on the 1st day of life and no sex-related difference on the 10th–14th days of life. The trend of reduced pineal function is a key point in understanding the neuroendocrine reactivity in male preterms. Future investigation of sex-related aspects of urinary 6-sulfatoxymelatonin excretion in children, especially premature infants, is required.


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