P-183 Cleavage patterns combined with fusion status at the compacting stage contribute to the selective single blastocyst transplantation
Authors: Wu L , Han W , Huang G 
Published: July 2024

Abstract

Study question
To investigate the impact of various cleavage patterns combined with fusion status at the compacting stage on the chromosome ploidy of blastocysts and possible reasons.

Summary answer
It can be inferred that in single blastocyst transfer without PGT-A, the normal cleavage incomplete compacted embryo can be selected as a last resort.

What is known already
Previous research has shown that embryos with abnormal cleavage patterns possess lower developmental potential; however, once a blastocyst is formed, its chromosomal euploidy is not necessarily inferior to that of embryos with normal cleavage. It is possible that these embryos undergo self-repair through unfused cells during the compactification stage. The question remains: what is the chromosomal ploidy of embryos with normal cleavage that have unfused cells or fragments at the compacting stage? Is it similar to the chromosomal ploidy of embryos with abnormal cleavage that have unfused cells at the compacting stage? This study aims to provide clarity.

Study design, size, duration
We conducted a retrospective analysis on 600 PGT-A cycles at our reproductive center from January 2020 to August 2022. A total of 2,250 blastocysts that underwent biopsy and PGT-A testing were included in our analysis. Of these, 475 blastocysts underwent single blastocyst transfer.

Participants/materials, setting, methods
We classified the embryos into four groups based on their cleavage patterns and fusion status at the compacting stage: normal cleavage complete compacting group (n = 1128), normal cleavage incomplete compacting group (n = 735), abnormal cleavage incomplete compacting group (n = 371), and abnormal cleavage complete compacting group (n = 16). We compared the chromosomal ploidy of four groups, as well as the composition of aneuploidy. We also compared live birth outcomes among the four groups following euploidy thawed single blastocyst transfer.

Main results and the role of chance
The chromosomal euploidy rates were 55.59%, 50.61%, 59.57%, and 62.5% in the normal cleavage complete compacting group, normal cleavage incomplete compacting group, abnormal cleavage incomplete compacting group, and abnormal cleavage complete compacting group, respectively. There was a significant difference in euploidy rates between the normal cleavage incomplete dense group and the abnormal cleavage incomplete dense group (P = 0.026). Additionally, there was a significant difference in chromosome deletion rates in abnormal chromosomes between the normal cleavage incomplete compacting group (23.95%) and the abnormal cleavage incomplete compacting group (15.63%) (P = 0.005). When thawing and transferring euploid single blastocysts, there was no significant difference in live birth outcomes among the four groups (P = 0.984).In early normal cleavage embryos, if there are unfused cells or fragments at the compacting stage, the ratio of chromosomal abnormalities increases, possibly due to chromosomal loss during the compacting stage. In contrast, abnormal cleavage embryos had an increased euploidy rate once they formed usable blastocysts. The live birth outcomes of abnormal cleavage diploid blastocysts are comparable to those of normal cleavage diploid blastocysts.

Limitations, reasons for caution
The limitation of this study is a retrospective study with a small sample size. The conclusions of the studies need to be validated in larger-scale prospective studies.

Wider implications of the findings
Embryologists prefer normal cleavage embryos over abnormal cleavage embryos, and this study found that the low euploidy ratio of normal cleavage incomplete compacting embryos can help guide the screening of single blastocyst transfer without PGT-A.

Trial registration number
not applicable