In this study we present the results of molecular-cytogenetic investigation of blood cells of fertile women of reproductive age. We used cultivated and uncultivated cells and two sets of FISH probes with direct and indirect labeling. The mean aneuploidy levels of 4 chromosomes were determined and statistical limits were scored. Aneuploidy levels determined in cultivated lymphocytes by multicolor FISH varied from 0.1 to 1.3%. The mean aneuploidy level for all chromosomes (13, 18, 21 and X) was 1.39%. The limit mutation detection was 3.4%. We found differences in results obtained with the use of direct and indirect labeling. It was shown that cultivating process influenced the aneuploidy level. Absolute error of FISH technique was 0.13%, relative error - 4.08%.