Cytoplasmic String Between ICM and mTE Is a Positive Predictor of Clinical Pregnancy and Live Birth Outcomes in Elective Frozen-thawed Single Blastocyst Transfer Cycles: a Time-lapse Study

Abstract

Background: In this study, we aim to investigate whether cytoplasmic string between inner cell mass (ICM) and mural trophectoderm (mTE) is a positive predictor of clinical pregnancy and live birth outcomes.Methods: 1,267 elective frozen-thawed single blastocyst transfer (eSBT) cycles cultured in time-lapse incubation system from January 2018 to May 2019 were involved in the study. Blastocysts were grouped according to the appearance of cytoplasmic strings between ICM and mTE cells, and identified as “Present” and “Absent” groups. In Present group, they were further categorized according to the quantity of cytoplasmic strings between ICM and mTE cells. Clinical pregnancy and live birth outcomes of blastocysts were used to evaluate the effect of cytoplasmic strings between ICM and mTE.Results: The baseline demographic and laboratory features were similar between the Present and Absent groups of cytoplasmic strings between ICM and mTE (P>0.05). According to the time-lapse analysis, cytoplasmic strings between ICM and mTE were more visible among good quality blastocysts. Furthermore, blastocysts with cytoplasmic strings showed a higher clinical pregnancy and live birth rates (P<0.05), and no significant differences were observed in abortion rate and birth weight (P>0.05).Conclusions: Although the previous conclusions of cytoplasmic strings were controversial, the present time-lapse analysis provides the evidence for the first time that cytoplasmic strings between ICM and mTE cells would be a positive predictor of clinical pregnancy and live birth outcomes in elective frozen-thawed single blastocyst transfer cycles.

Detailed analysis of cytoplasmic strings in human blastocysts: new insights

“…Additionally, 59.0% of blastocysts had CS first appear during early blastulation and cease activity during the expansion stage of blastulation (49.1%). Two other studies have reported the presence of CS to be related to the grade of blastocoel expansion (Ebner et al, 2020;Ma et al, 2021). Similarly, the current study also indicated that the stage of expansion was related to CS presence, with a bivariate regression analysis suggesting that the chances of detecting CS in hatching blastocysts were 2.13 times more probable compared with expanded blastocysts.…”

“…These observations did not translate to a reduction in embryo fate of the live birth rate. Other researchers have found the presence of CS to have a positive effect (Eastick et al, 2021;Ma et al, 2021) or at the least no effect (Alpha Scientists in Reproductive Medicine and ESHRE Special Interest Group of Embryology, 2011; Ciray et al, 2014;Ebner et al, 2020) on blastocyst viability.…”

“…These ultrastructures are present during blastulation, and currently their function and role in human blastocysts are of unknown significance. Little information exists in the published literature (Ducibella et al, 1975;Salas-Vidal and Lomelí, 2004;Fierro-González et al, 2013), however recently a few studies have identified CS as a potential biomarker that may aid in the selection of blastocysts that have higher implantation potential for transfer (Eastick et al, 2021;Ma et al, 2021). In addition, it has been reported that CS did not have a negative effect on implantation (Ebner et al, 2020), contrary to a previous study (Scott, 2000).…”

The importance of cytoplasmic strings during early human embryonic development

“…Investigation of the presence and function of cytoplasmic strings in the human blastocyst is a controversial topic among embryologists ( Scott, 2000 ; Hardarson, Van Landuyt, and Jones, 2012 ; Ebner et al, 2020 ; Ma, Jin, and Huang, 2020 ; Eastick et al, 2022a ). In addition, the study on the relationship between the presence of cytoplasmic strings and the embryo viability in human in vitro fertilised embryos has received considerable attention.…”

“…In the early 2000s, the occurrence of cytoplasmic strings at the blastocyst stage was classified as a negative sign of embryo viability ( Scott, 2000 ), but more recently, it has been described as a positive feature ( The ESHRE Capri Workshop Group, 2010 ; Ebner et al, 2020 ; Ma, Jin, and Huang, 2020 ; The ESHRE Capri Workshop Group, 2020 ; Eastick et al, 2021 ). However, the importance and clinical significance of this structure are still controversial.…”