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

Abstract

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 Statement

• What 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.

Keywords:

• Assisted reproduction
• blastocyst
• day 3 embryo
• embryo assessment
• embryo quality

Acknowledgements

We wish to thank the members of other Reproductive Medical Center, Weihai Maternal and Child Health Care Hospital members, for their valuable input in this study.

Author contributions

Ji Liu and Honghui Wang contributed to conception and design of study; Yanhua Zhou, Lingxi Tong, Xiaoxiao Wang and Yanhong Li contributed to acquisition of data; Ji Liu and Yanhua Zhou contributed to analysis and interpretation of data; Honghui Wang drafted the manuscript; Honghui Wang and Ji Liu critically revised the manuscript. All authors have read and approved the final manuscript.

Disclosure statement

The authors report no conflict of interest.

Data availability statement

The datasets used and/or analysed during the current study are available from the corresponding author on reasonable request.

Additional information

Funding

This work was supported by project ZR2020QC101 supported by Shandong Provincial Natural Science Foundation.