PREGNANCY OUTCOME OF TRANSFERRED EMBRYOS WITH MOSAICISM AND SEGMENTAL VARIATIONS

Abstract

Mosaic embryos are characterized by the presence of chromosomally different cell lines within the same embryo. Typically, mosaic embryos were not transferred in IVF treatments because, similar to aneuploidy embryos, they were considered abnormal. However, in a recent study we have demonstrated that euploid/diploid mosaic embryos hold the potential to implant and result in the birth of healthy babies. As a consequence, the transfer of these embryos is now offered as an option for women who undergo IVF resulting in mosaic embryos but no euploid embryos. Although the impact of mosaicism on the implantation and developmental potential of embryos is not fully known, it is reasonable to assume that it is likely to influence the clinical outcome of IVF treatments. We also hypothesized that the extent of mosaicism and the type of aneuploidy involved may affect the IVF success rate. However, no definitive conclusion could be drawn because our study was small and the data available were insufficient to test this hypothesis. The aim of this study was to assess whether the extent of mosaicism and the type of the type of aneuploidy may influence the development potential of mosaic embryos. To test this hypothesis we enlarged our previous study, offering the transfer of mosaic embryos, at different aneuploidy percentage and aneuploidy content, to 200 women for which the IVF/PGT cycle resulted in no euploid embryos available for transfer. Comprehensive chromosome testing was performed using high resolution next generation sequencing (NGS) methodology. The clinical outcome obtained after transfer of mosaic embryos with low ( We found that the reproductive potential of a mosaic euploid/aneuploid blastocyst is inversely correlated with the abnormal-to-normal cells ratio. Mosaic embryos with a high percentage of chromosomally abnormal cells (≥50%) resulted in a statistically significant reduction in clinical pregnancy rate/ET, implantation rate, and live-birth rate compared with mosaic embryos with a lower aneuploidy percentage ( In conclusion, the results of our study demonstrated that mosaic embryos have poorer clinical outcomes compared with euploid embryos and that their implantation and developmental potential is influenced by the extent of mosaicism and the aneuploidy content.