Background. During pregnancy many women suffer from lower urinary tract symptoms (LUTS). The etiology and pathogenesis of urinary loss during pregnancy remain still unclear. Normal pregnancy is known to be associated with functional changes in various physiological systems. Changes of kidney function, on the one hand, are the part of physiological changes during pregnancy, on the other hand - can promote urinary incontinence. Purposes. The purpose of this study was to estimate the role of kidney function changes in development of LUTS during pregnancy. Materials and methods. A total of 270 women with the physiological course of pregnancy (83 in the I first trimest, 78 - in the II trimester and 109 - in the III trimester) aged from 18 till 44 years, with no LUTS before the current pregnancy were examined. Blood serum and urine osmolality was determined with MT-4 milliosmometer (“Burevestnik”, Russia); the concentration of serum and urine creatinine, sodium, potassium and magnesium ions were determined with automatic Abbott Architect 8000 analyzer. LUTS are revealed in 81.9 ± 2.3% of pregnant women. Urinary loss in pregnant women is combined with increase in diuresis. Grater diuresis is due to increasing osmotically active substances excreation, precisioly sodium. Rise in nocturnal diuresis does not lead to inversion of circadian rhythm of urine production. A direct correlation has been found between urine output and glomerular filtration rate.