P–259 Blastocyst quality is associated with both the start and the duration of compaction after ICSI

Abstract Study question Is the start and the total duration of compaction related to embryo quality? Summary answer The timing of the start, the end and the total duration of compaction are associated with blastocyst quality grade in the IVF laboratory. What is known already Preimplantation embryo development follows a programmed timeline during which a series of critical events take place. One event typically occurring on day 3/4 post fertilisation is the formation of adherence junctions between blastomeres in a process called compaction. It is considered the first morphological event in the differentiation process of the mammalian embryo. Evaluation of developmental events are used to optimize the selection of the most competent embryos for transfer and/or cryopreservation in the IVF laboratory. It has already been shown that the time of full compaction is indicative for high-quality blastocysts with a higher implantation rate. Study design, size, duration A single-centre retrospective observational study including 74 ICSI cycles performed in 2020. Injected oocytes were cultured in blastocyst medium (Origio) in the EmbryoScope + (Vitrolife) for 5/6 days. Embryos that reached the blastocyst stage were evaluated for the start of compaction, the time to reach full compaction and the total duration of compaction. These parameters were compared between good- and poor-quality blastocysts; the primary outcome parameter of the study was embryo quality. Participants/materials, setting, methods Only ICSI cycles with ejaculated fresh/frozen-thawed sperm and monitored in time-lapse incubator were included. All MNC, IVM and PGT cycles were excluded. Time zero was the start of ICSI. Good-quality embryos were full and expanded blastocysts with good-quality inner cell mass and trophectoderm (AA, AB, BA and BB according to Gardner and Schoolcraft (1999)). GraphPad Prism was used for statistical analysis. After testing for normality and homogeneity, unpaired t-test or Mann-Whitney test determined significant differences. Main results and the role of chance In this study, of the 528 included 2PN oocytes, 229 (43.4%) reached the blastocyst stage and 299 (56.6%) were arrested. Among the former, 131 (57.2%) blastocysts were classified in the good-quality group and 98 (42.8%) blastocysts in the poor-quality group. In general, human embryos compacted slowly while dividing further and the blastomeres moved during the compaction process. The start of compaction was heterogeneous