31. CHROMOSOMAL MOSAICISM AS A RISK FACTOR FOR INCORRECT RESULTS OF PGT-A

Introduction Mosaicism may cause discordance between the result of PGT-A and the karyotype of cells outside the biopsy area. How likely is the risk of incorrect results of PGT-A due to chromosomal mosaicism? The aim of present study was comparison of molecular karyotypes of trophectoderm cells and inner cell mass. The study presents the results of re-analysis of the molecular karyotypes of 10 embryos by the comparative genomic hybridization on microarrays (aCGH). Material & methods Initially, the trophectoderm biopsy was performed for all 10 embryos for PGT-A using the aCGH analysis (24sure, Illumina). All 10 trophectoderm samples were found to be aneuploid. Corresponding embryos were not recommended for transfer and were included in this study per patients’ informed consent. All embryos were divided into 2 parts: trophectoderm (TE) and the inner cell mass (ICM). Each part was analyzed separately. For 2 embryos blastomeres (B) not included in the blastocyst were also available (for embryos №2 and №3). Re-analysis was performed using the aCGH analysis (24sure, Illumina). Results Molecular karyotypes of TE cells and ICM 7 of 10 embryos coincided with PGT-A results. Molecular karyotypes of 3 samples demonstrated incomplete concordance with the PGT-A results. We detected mosaic form of aneuploidies of sex chromosomes in the inner cell mass of embryo №10. PGT-A result of this sample contains information about whole aneuploidy of sex chromosomes. Mosaic form of reciprocal aneuploidy was observed in the ICM of embryo №4. Additional monosomy of chromosome 16 was detected in TE of embryo №8. This aneuploidy was not detected in the ICM and in the trophectoderm biopsy sample for PGT-A. No preferential localization of abnormal cells in trophectoderm or inner cell mass was observed. The study has limitations: a) the complete separation cells one by one and TE from ICM at blastocyst stage is impossible; b) there is a risk of false determination of the localization of aneuploidy in the embryo and the risk of inability to detect aneuploidy in the case when the sample contains reciprocal aneuploidy. Conclusions Our results show the coincidence of the molecular karyotypes of different embryo's cells was detected for most samples. In cases of detection of mosaic aneuploidy in ICM, cells with the whole aneuploidy and the normal molecular karyotype were also present in TE. None of the 10 embryos was suitable for transfer per any sample results. Further research is required with increasing sample size.