O-119 Time-lapse comprehensive portrait of cytoplasmic strings appearing during blastulation: prevalence and implications for embryo assessment.

Abstract Study question What are the prevalence and implications of cytoplasmic strings (Cyt-S) in preimplantation development after blastulation? Summary answer Cyt-S common human embryos associated with faster blastocyst development, larger expansion, better morphological quality. is known already dynamic cellular projections connecting inner-cell-mass (ICM) trophectoderm during expansion. Their vitro has been estimated 44-93%. Currently, their role unknown. Studies animal models suggested they might be involved ICM-to-trophectoderm communication or cell fate-related events. Nevertheless, comprehensive descriptions clear definitions, evidence-based hypotheses about function, data clinical lacking, limited controversial. Here we leveraged time-lapse microscopy, artificial intelligence, chromosomal testing to comprehensively portray these features blastulation expansion processes. design, size, duration Observational study involving 124 PGT-A cycles EmbryoScope (Vitrolife) ≥1 (N = 315) between May-2013 November-2014. Timings from tSB biopsy (t-biopsy, i.e., full-expansion) hours-post-insemination (hpi) embryo area (including zona-pellucida µm2) were automatically annotated through an AI-based software (CHLOE™, Fairtility). One senior embryologist presence, number, timings, type (thick cell-to-cell connections and/or threads), collapses (i.e., reduction preventing discrimination ICM trophectoderm). Participants/materials, setting, methods ICSI, continuous culture (day 5-7) incubators, without drilling on fully-expanded blastocysts, qPCR assess non-mosaic full-chromosome aneuploidies all conducted. Blastocyst quality was defined according Gardner’s schemes as excellent (AA), good (AB,BA), average (BB,AC,CA) poor (CC,BC,CB). Only vitrified-warmed euploid single-embryo-transfers performed. Along developmental extent quality, also assessed euploidy live-birth rates blastocysts Cyt-S. Main results chance 94.4% patients 117/124) had (mean:2.2±1.6, range:0-9). 86% analyzed 271/315) (3.5±2.1, 1-13; longest Cyt-S: 5.8±3.4 hours, 0.5-20.9). Overall, 937 detected at 117.3±11.8 hpi (85.7-160.5) lasting 3.8±2.7 hours (0.2-20.9). The first each lasted longer (4.4±3.2 hours) compared following (≈3 less). mostly threads 133/271, 54.2%) thick becoming 382/937, 40.8%) than constant diameter 47/937, 5%). Of 271 Cyt-S, 71.9% showed only early processes 195; 3.0±1.6, 1-10), 7.7% 21; 2.6±1.5, 1-6), 20.3% both 55; 2.3±1.3 3.2±2.4, 1-11 respectively). Poor- versus excellent-quality 54/75, 72% N 120/129, 93%, multivariate-OR=0.32, 95%CI 0.11-0.92, adjusted-p=0.03), t-biopsy (multivariate-OR=0.97, 0.95-0.99, p 0.05) (multivariate-OR=1.1, 1.01-1.18, 0.02) Lastly, while comparable association instead shown live-birth-rates per transfers 34/77, 44.2% 0/10, 0%; < 0.01), although very preliminary. Limitations, reasons for caution Some correspond present before Larger datasets required confirm putative associations outcomes. could reported here, but not causations/consequences. Specific basic research studies this end Wider findings Embryos reaching timings (tSB t-biopsy) expand, achieved a morphology. These physiological represent biomarkers function yet unknown Trial registration number applicable