Abnormal cleavage patterns in embryos are associated with aneuploidy and poor morphology scores

Abstract

Morphokinetic parameters as measured through time-lapse imaging may predict embryonic developmental potential. While there are several studies on the timing of early cell divisions, there are limited data on abnormal cleavage (AC) events and their relationship to embryo quality. An AC is the division from a mother blastomere cell to three daughter cells. This is thought to be secondary to abnormal mitotic spindle assembly, leading to an abnormal segregation of chromosomes. Previous studies report that embryos exhibiting ACs have decreased blastulation and worse implantation rates. In our study, we sought to determine if ACs are associated with aneuploidy. We also evaluated the relationship between ACs and developmental potential as well as day 3 and day 5 morphologic scoring. Our primary objective was to determine if ACs are related to ploidy status. Secondary objectives were to determine if ACs are correlated with blastulation rates and with embryo morphologic scores at the cleavage and blastocyst stages. Previously cryopreserved human embryos donated for research were thawed and cultured in the Miri Time-lapse incubator for 6 days. A staff embryologist recorded standard time-lapse parameters and day 3 and 5 morphology assessments. Trophectoderm biopsies were performed on embryos that grew to blastocysts on day 5 or 6. Otherwise whole embryos were sent for preimplantation genetic screening (PGS). Next generation sequencing was used to determine embryo ploidy status. Morphologic grading of embryos was performed per Society of Assisted Reproductive Technology guidelines for cleavage stage embryos. We used methods for blastocyst morphologic grading described by Gardner, et al with minor modifications. Statistics were performed using Chi-square, Fisher’s Exact, ANOVA, and logistic regression. 50 embryos were included our analysis. 32/50 (64%) of thawed embryos grew to the blastocyst stage. 35/50 (70%) of embryos were euploid. ACs were visualized in 15/50 (30%) embryos. 8/15 (53.3%) of these embryos experienced an AC after the 1st cytokinesis. 7/15 (46.7%) of embryos had ACs after the 2nd cytokinesis. 4/15 (26.7%) embryos had more than 1 AC event. Aneuploid embryos had a significantly higher percentage of AC events (73.3% vs 22.9%, p<0.001). AC events did not reliably predict which embryos grew to the blastocyst stage or those that arrested. Embryos that had at least 1 AC took an average of 10.7 hours longer to develop from a morula to a fully expanded blastocyst compared to those without ACs (β=10.7, p=0.01). Cleavage stage morphology scores did not correlate with ACs. In blastocysts with ACs, there was a higher proportion of poor quality embryos compared with good/fair embryos (66.7% vs 33.3%, p=0.03). Based on our findings, ACs were more likely to occur in aneuploid embryos. While they did not predict blastocyst formation, they were associated with delayed blastulation and with poor blastocyst morphology scores. When selecting embryos for transfer, particularly those not undergoing PGS, those with ACs may have a worse prognosis for achieving a successful pregnancy.