P-133 Cytoplasmic strings between inner cell mass and trophectoderm: novel predictors of euploid blastocysts’ implantation competence
Year: 2025
Type: conference-abstract
Abstract: Study question Could the presence, quantity, and type of cytoplasmic strings (Cyt-S) serve as biomarkers for the implantation competence of euploid blastocysts? Summary answer The absence of Cyt-S during blastulation dynamics is associated with a lower live birth rate (LBR) per transfer. What is known already Cyt-S are dynamic cellular projections observed in most human embryos, connecting the inner cell mass (ICM) to the trophectoderm during blastulation. Their presence, number, and type correlate with embryo viability, morphological quality, and blastocyst expansion, though their exact function remains unclear and only hypothesized from animal models in the 90s. Preliminary data suggest Cyt-S may also serve as biomarkers of implantation competence. This study evaluated Cyt-S presence, number, and type in euploid blastocysts, investigating their association with clinical, gestational, and neonatal outcomes following embryo transfer, aiming to clarify their potential role in predicting implantation success and overall reproductive outcomes. Study design, size, duration Retrospective observational study (2015-2020) of 539 transferred euploid blastocysts. Timings from tSB (start of blastulation) to t-biopsy (time-of-biopsy) in hours-post-insemination (hpi) were recorded along with Cyt-S presence, number, and type [bridges (B), threads (T), or B transitioning to T (B-T)], and timings of appearance and fading. Associations between Cyt-S and positive pregnancy test (PPT) and LBR per transfer, biochemical pregnancy loss per PPT, miscarriage rate (MR) per clinical pregnancy, gestational and neonatal outcomes were assessed. Participants/materials, setting, methods ICSI, continuous blastocyst culture (days 5-7) in Embryoscope incubator, trophectoderm biopsy on fully-expanded blastocyst without previous zona-pellucida drilling and comprehensive-chromosome-testing were performed. Blastocyst quality was classified according to Gardner’s criteria as excellent (AA), good (AB,BA), average (BB,AC,CA) and low (CC,BC,CB). Only vitrified-warmed single euploid blastocyst transfers were performed, with endometrial preparation using modified natural or artificial cycles. Regression analyses were conducted adjusting for confounders and using Generalized Estimating Equations (GEE). Main results and the role of chance 369 patients (age at retrieval:38±3.2 years; age at transfer:38±3.3 years; BMI:22±3.8 kg/m²) underwent 539 transfers. 63% of all euploid blastocysts analyzed (N = 341/539) had ≥1 Cyt-S (mean:2.4±1.5, range:1-9, mostly T or B-T [96%], the first appearing at 111.5±10.8 hpi, the last disappearing at 116.3±10.6 hpi). Euploid blastocysts without Cyt-S (Cyt-S-) were 3-4 hours slower than control (Cyt-S+) at both tEB and t-biopsy, and of lower morphological quality (AA:59.1% versus 69.5% and CC/BC/CB:20.7% versus 12.3%, p = 0.025). In Cyt-S- versus Cyt-S+, PPT was lower (43.9% versus 62.5%, p < 0.001), and BPL was higher (25.3% versus 9.9%, p < 0.001). Indeed, lower LBR was reported in the absence of Cyt-S (N = 50/198, 25.3%, 95%CI:19.7-31.8 versus N = 163/341, 47.8%, 95%CI:42.6-53.1; OR adjusted for morphological quality and t-biopsy=2.5, 95%CI: 1.7-3.7, p < 0.001, power=99.9%). Number and type of Cyt-S were not associated. No difference was reported in Cyt-S- versus Cyt-S+ for gestational age (36.2 versus 37.9 weeks), birthweight (3136 versus 3251 g), normal for gestational age rate (82% versus 79%), prevalence of gestational complications (12% versus 6%) and of minor/major neonatal malformations (2% versus 1.3%). Also Cyt-S number and type showed no associations. All data were confirmed by GEE, and among first embryo transfers conducted by each patient. Limitations, reasons for caution Retrospective single center study. Cyt-s were assessed manually. Larger datasets are needed to validate the associations between Cyt-S and clinical outcomes. Cyt-S were not used to rank embryos for transfer, though their absence was linked to lower blastocyst quality and slower development. Wider implications of the findings Emerging evidence suggests Cyt-S presence is linked to euploid blastocyst implantation, independent of morphology and timing, warranting consideration in embryo prioritization. However, Cyt-S function remains unclear. Further research should explore their role by comparing species and investigating the effects of interfering with Cyt-S dynamics. Trial registration number No
Source: Human Reproduction
Language: English
Subfield: Reproductive Medicine
Field: Medicine
Domain: Health Sciences
Open Access status: bronze
OpenAlex ID: W4411757486