Developmental potential of different embryos on day 3: a retrospective study

To investigate how different quality of day 3 (D3) embryos affect blastocyst formation and clinical outcomes. This retrospective study analysed 699 patients undergoing assisted reproductive technology (ART) between January 2017 and February 2021. A total of 2517 D3 embryos were transferred to blastocyst medium for extended culture. D3 embryos were divided into five groups. Grade A, 6-10 cells, symmetrical blastomeres and <20% fragmentation; grade B, 6-10 cells, uneven blastomeres and ≥20% fragmentation; grade C, >10 cells, symmetrical blastomeres and <20% fragmentation; grade D, >10 cells, uneven blastomeres and ≥20% fragmentation; grade E, <6 cells. Status of day 5 (D5) and day 6 (D6) blastocysts and the clinical outcomes (blastocyst transfer) of each D3 embryo were recorded. The grade C group showed a higher D5 blastocyst formation rate and a high-quality blastocyst rate than other groups (p<.05). However, the clinical pregnancy rates in the grade A group were higher than other groups (p<.05). Embryos with low speed of development (grade E group) showed considerable clinical outcomes that were still worth investigating. D3 embryos with less fragmentation and ≥6 symmetrical blastomeres revealed a higher developmental potential, while embryos with 6-10 blastomeres showed the ideal clinical outcomes.Impact StatementWhat is already known on this subject? Accurate embryo evaluation can effectively reflect the developmental potential of different embryos. The number of blastomeres, proportion of fragmentation, and blastomere symmetry are three important and popular morphologic parameters used for evaluating day 3 (D3) embryos. However, in existing reports, combining these three parameters for embryo evaluation often results in different results. This is because different researchers have chosen different criteria for these three parameters.What do the results of this study add? In this retrospective study, we summarised the medical records of our reproductive centre in the past three years, redefined the evaluation method of the D3 embryos, and analysed the corresponding developmental potential and clinical outcomes. We conclude that although the embryonic development potential of grade C embryos (>10 cells, symmetrical blastomeres and/or <20% fragmentation) is relatively good, the results of grade A embryos (6-10 cells, symmetrical blastomeres and/or <20% fragmentation) are better in terms of clinical outcomes.What are the implications of these findings for clinical practice and/or further research? We believe this is meaningful for embryologists to choose embryos for transfer and predict the clinical outcome of IVF cycles.