A morphological and chromosomal study of blastocysts developing from morphologically suboptimal human pre‐embryos compared with control blastocysts

BACKGROUND: IVF laboratories performing embryo transfer at day 2 or 3 after fertilization are currently discarding pre‐embryos considered suboptimal using morphological criteria. The objective of this study was to investigate whether blastocysts, cultured from such pre‐embryos (surplus), were chromosomally and morphologically normal. As a control group we used morphologically good quality embryos (GQE), cultured to the blastocyst stage. METHODS: Human pre‐embryos considered suboptimal were cultured to the blastocyst stage. As a control group, frozen–thawed pre‐embryos of good quality were cultured under identical conditions. The chromosomal status of the blastocysts obtained was studied by multi‐colour fluorescence in‐situ hybridization for chromosomes 13, 16, 18, 21, 22, X and Y. RESULTS: There is, on average, a significantly higher degree of chromosomal aberrations in blastocysts derived from surplus pre‐embryos compared to blastocysts derived from GQE, and the chromosomal aberrations are generally found in a higher number of blastomeres per blastocyst. In addition, blastocysts from surplus pre‐embryos had significantly poorer morphology compared to GQE. Improvement in morphology and/or developmental rate in surplus pre‐embryos between day 2 and day 3 did not predict a morphologically/chromosomally normal blastocyst. However, this study shows that close to half of the surplus pre‐embryos that reach the blastocyst stage can be considered chromosomally normal when assessed for these seven chromosomes. Furthermore, we found that chromosomal aberrations were more concentrated in a particular cell population within blastocysts derived from GQE, compared with surplus blastocysts. CONCLUSIONS: The study suggests that even if the IVF laboratory is on average making the correct decision about the potential of a pre‐embryo, surplus pre‐embryos that might become chromosomally normal blastocysts are still being discarded.