Blastocyst Morphology Holds Clues Concerning The Chromosomal Status of The Embryo

BACKGROUND: Embryo morphology has been proposed as an alternative marker of chro- mosomal status. The objective of this retrospective cohort study was to investigate the association between the chromosomal status on day 3 of embryo development and blas- tocyst morphology. MATERIALS AND METHODS: A total of 596 embryos obtained from 106 cycles of intra- cytoplasmic sperm injection (ICSI) followed by preimplantation genetic aneuploidy screening (PGS) were included in this retrospective study. We evaluated the relation- ship between blastocyst morphological features and embryonic chromosomal altera- tion. RESULTS: Of the 564 embryos with fluorescent in situ hybridization (FISH) results, 200 reached the blastocyst stage on day 5 of development. There was a significantly high- er proportion of euploid embryos in those that achieved the blastocyst stage (59.0%) compared to embryos that did not develop to blastocysts (41.2%) on day 5 (P<0.001). Regarding blastocyst morphology, we observed that all embryos that had an abnormal inner cell mass (ICM) were aneuploid. Embryos with morphologically normal ICM had a significantly higher euploidy rate (62.1%, P<0.001). As regards to the trophectoderm (TE) morphology, an increased rate of euploidy was observed in embryos that had nor- mal TE (65.8%) compared to embryos with abnormal TE (37.5%, P<0.001). Finally, we observed a two-fold increase in the euploidy rate in high-quality blastocysts with both high-quality ICM and TE (70.4%) compared to that found in low-quality blastocysts (31.0%, P<0.001). CONCLUSION: Chromosomal abnormalities do not impair embryo development as ane- uploidy is frequently observed in embryos that reach the blastocyst stage. A high-quality blastocyst does not represent euploidy of chromosomes 13, 14, 15, 16, 18, 21, 22, X and Y. However, aneuploidy is associated with abnormalities in the ICM morphology. Further studies are necessary to confirm whether or not the transfer of blastocysts with low-quality ICM should be avoided.