Blastocyst Morphology Holds Clues Concerning The Chromosomal Status of The Embryo

Background: Embryo morphology has been proposed as an alternative marker of chromosomal status. The objective of this retrospective cohort study was to investigate the association between the chromosomal status on day 3 of embryo development and blastocyst morphology. Materials and Methods: A total of 596 embryos obtained from 106 cycles of intracytoplasmic sperm injection (ICSI) followed by preimplantation genetic aneuploidy screening (PGS) were included in this retrospective study. We evaluated the relationship between blastocyst morphological features and embryonic chromosomal alteration. 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 higher 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 normal 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 aneuploidy 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.