P-278 The presence of fragmentation during embryo cleavage does not reflect the chromosomal status of the blastocysts
Authors: Medrano M.D.L.L , Parrella A , García Sifre A , Galiana Briones Y , Ramos Mas B , Morales Navarro L , Soler Balaguer N , Aizpurua J 
Published: June 2022

Abstract

Study question
Does the presence of fragmentation at day-2 and day-3 of embryo development correlate with blastocyst formation and chromosomal status?

Summary answer
Embryos with high fragmentation have low chances to develop into blastocysts due to cytoplasmic incompetence. However, there is no correlation between aneuploidy and embryo fragmentation.

What is known already
The assessment of cleavage stage embryos is carried out with the evaluation of some morphological features such as fragmentation rate, irregularities in blastomeres, multinucleation and the blastomere number. It has been described that the fragments formed during cell division are responsible for the arrest and necrosis of the adjacent blastomeres; Moreover, they may hinder the blastomeres’ division planes that increase the change of abnormal compaction, cavitation, and blastocyst formation. Studies have searched for a link between aneuploidy and altered embryo morphology. However, it is unknown if the blastocyst with high fragmentation at the cleavage stage can lead to chromosomal abnormalities.

Study design, size, duration
From March 2019 to December 2022, couples (N = 175) underwent 190 ICSI cycles with donor oocytes and had their embryos tested through Pre-implantation Genetic Test for Aneuploidy (PGT-A). We evaluate the degree of fragmentation at their day-2 and day-3 of development of 1765 embryos and compare the blastocyst, euploidy, implantation and clinical pregnancy rate (CPR) between embryos with grade 1 and 2 (Grade 1-2) and those with grade 3 and 4 (Grade 3-4) of fragmentation.

Participants/materials, setting, methods
The embryo score was assigned according to the following cleavage grading system: grade-1 with 0% of fragmentation, grade-2 with 0-10%, grade-3 with &gt;10-25% and grade-4 with 25-50%. Implantation, CPR and delivery rate were calculated per transferred embryo. Embryo quality was assessed with time-lapse technology (Geri®), PGT-A test was carried out on blastocyst’s trophectoderm using NGS (Illumina®). All analysis were conducted using SPSS software.

Main results and the role of chance
This retrospective study includes 175 couples who underwent 190 ICSI cycles using donor oocytes. A total of 2518 oocytes were injected with ICSI procedure achieving a fertilization rate of 73.8% (1858/2518). Of these, 93 fertilized oocytes were excluded from the study because they showed no cell division at day-1 of their development. Significant difference was seen in the number of embryos that reached the blastocyst stage. The blastocyst rate of grade 1-2 embryos was 60.4% (815/1348) compared to 16.8% (70/417) of those with grade 3-4 (P &lt; 0.0001). Interestingly, comparable euploidy rate was found between grade 1-2 and grade 3-4 embryos being 69% (548/794) and 68.5 % (48/70), respectively (P=NS). Although Implantation and CPR decrease from grade 1-2 to grade 3-4, no significant difference was found. The implantation rate was 44.2% (104/235) and 36.8% (7/19) while CPR was 59.6% (93/156) and 36.8% (7/19) in grade 1-2 and grade 3-4 group, respectively (P=NS). Pregnancy loss was 16.1% (15/93) in grade 1-2 and 5.2% (1/19) in grade 3-4 (P=NS).

Limitations, reasons for caution
This study was carried out on donor oocytes to exclude any female factor that could have affected the euploidy rate. Therefore, the number of patients is limited. Moreover, Implantation parameters like receptivity or immunologic disorders weren’t addressed. No data have been included on perinatal and obstetrical outcomes for pregnancies.

Wider implications of the findings
This study demonstrated that although embryos with high fragmentation have a lower change of reaching the blastocyst stage, the fragmentation parameter doesn’t reflect the chromosomal status of the resulting blastocysts.

Trial registration number
N/A