The aim of the study was to assess the diagnostic potential of SNP-based chromosomal microarray analysis for detecting pathogenic copies number variations (CNVs) in fetuses with a normal karyotype, in which an increase in the nuchal translucence of >2.5 mm was detected by ultrasound at a gestational age of 11 weeks to 13 weeks 6 days.Materials and Methods. The study included 225 pregnant women who underwent invasive prenatal diagnostic procedures following the detection of an isolated thickening of the fetal nuchal fold. The fetal material obtained was examined using a cytogenetic test; if a normal karyotype was confirmed, chromosomal microarray analysis was performed as a second-line test.Results. Pathogenic CNVs were detected in 22 of 225 fetuses (9.8%) with a normal karyotype. Of these 22 fetuses, pathogenic CNVs not classified as syndromes were detected in 14 cases (63.6%), and those previously described as syndromes -in 8 cases (36.4%). In 9 fetuses (41%), CNVs in two non-homologous chromosomes were determined; these findings indicated a high likelihood of carrying balanced translocations in the parents. Indeed, when analyzing the parent's karyotype, in 8 out of 9 couples, balanced translocations were found in one of the parents. Conclusion.Using chromosomal microarray analysis in fetuses with a thickened nuchal fold makes it possible to increase the ability to detect chromosomal imbalances, including those caused by pathological meiotic segregation of parental reciprocal translocation.

Introduction. The prevalence of congenital malformations (CMFs) in fetal central nervous system (CNS) ranges from 1.5 to 3 % and covers around 29 % among all malformations, whereas percentage in the structure of perinatal and infant mortality reaches 25–26 %.Aim: to estimate frequency of pathogenic copy number variations (CNVs) in fetuses with congenital malformations of CNS and normal karyotyping cytogenetic analysis.Materials and Methods. There were enrolled 42 pregnant women underwent invasive prenatal diagnostics in 2013–2019 due to ultrasound detection of congenital CNS defect in fetus. Fetal samples were studied by using chromosome microarray analysis (CMA).Results. Various pathogenic CNVs were detected in 7 (16.6 %) fetuses with prenatally diagnosed congenital CNS malformations. Non-syndrome pathogenic CNVs were detected in 85.7 %.Conclusion. Thus, performing chromosome microarray analysis as the first-line assay allows to diagnose not only aneuploidy, but also microdeletion/microduplication, the size of which below resolution threshold for standard cytogenetic karyotyping