The Influence of Day 2 Blastomere Symmetry on Blastocyst Grade and Ploidy Status

Abstract

Previous studies have suggested that aneuploidy rates are co-related with cell asymmetry at the cleavage stage. A retrospective study was carried out to determine the significance of blastomere symmetry at the 4-cell stage on blastocyst grade and ploidy status. 732 Day 5/6 blastocysts from 191 patients undergoing Pre-implantation Genetic Testing for Aneuploidy were analysed with time-lapse imaging (Embryoscope, Vitrolife) during 2017. Blastomere symmetry was measured at the first image of 4-cells on Day 2 by tabulating the mean diameter of 2 lines drawn perpendicularly on each blastomere. Symmetry was defined as the blastomere diameter difference of [Formula: see text] 25%. Trophectoderm (TE) biopsy was performed on Day 5/6 followed by chromosomal evaluation using Next Generation Sequencing (VeriSeq Protocol, Illumina). Blastocyst grade was classified as either “Good” (inner cell mass (ICM) and TE, AA respectively), “Fair/Good” (AB, BA), “Fair” (BB) and “Poor” (early blastocyst grade 2 or TE grading of C). The significance of blastomere symmetry on blastocyst grade and ploidy status was measured using chi-square tests. There was no significance difference in resulting blastocyst quality for symmetrical and asymmetrical embryos (Table 1: p [Formula: see text] 0.10). Furthermore, there was no significance difference in the euploid rate (42.5% vs. 45.3%) or mosaic rate (22.1% vs. 16.2%) between symmetrical and asymmetrical embryos (p [Formula: see text] 0.24). In conclusion, the presence of asymmetrical blastomeres at the 4-cell stage do not impact the good quality blastocyst formation rate and euploidy rate for embryos that progress into blastocysts. However, this study excludes embryos that do not develop to the blastocyst stage and those with erratic division patterns, direct cleavage and reverse cleavage on Day 2, both of which have potential to influence ploidy result. Asymmetrical 4-cell embryos have the potential for high quality euploid blastocyst progression and can be considered for day 2 embryo transfer in the absence of symmetrical 4-cell embryos.