Human frozen-thawed blastocyst morphokinetics observed using time-lapse cinematography reflects the number of trophectoderm cells

Abstract

Recent studies reported morphokinetic indices for optimal selection of embryos in assisted reproductive technology (ART). The morphokinetics in blastocyst stage include the collapse and re-expansion rates after thawing. However, evaluation methods using these morphokinetics have not been established, mainly because the underlying molecular mechanisms remain unclarified. In this study, we focused on the relationship between these morphokinetic observation of the blastocyst behaviour and the number of cells constituting the blastocyst. We evaluated 38 surplus human frozen-thawed blastocysts using time-lapse cinematography and recorded their expansion, contraction, and hatching. A total of 28 blastocysts expanded in culture (cross-sectional area ≥ 5,000 π μm2). In comparison to the ones that did not, the expanded group presented significantly more number of inner cell mass (ICM) and trophectoderm (TE) cells, which eventually develop into the fetus and placenta, respectively (ICM: Expanded 10.2 ± 6.3 vs. Non-Expanded 6.0 ± 12.3, p < 0.05; TE: Expanded 165.7 ± 74.8 vs. Non-Expanded 57.0 ± 29.4, p < 0.05). Moreover, a positive correlation was found between the expansion rate (up to 4 h) and the number of TE cells (r = 0.558, p = 0.0021). Additionally, blastocysts that hatched had a significantly higher number of TE cells than those that did not (hatching 225.2 ± 61.2 vs. no hatching 121.1 ± 48.6, p < 0.0001). The number of TE cells per unit of cross-sectional area correlated negatively with the contraction time (r = –0.601, p = 0.0007). No correlation between the number of ICM cells and these morphokinetics was detected. In conclusion, our study demonstrates that different morphokinetics of frozen-thawed blastocysts reflect the number of TE cells. The differentiation of blastocysts containing sufficient TE cells would be beneficial for implantation and prognosis of a subsequent pregnancy. Thus, evaluation of these morphokinetics can be an effective method to screen good embryos for ART.

SOX2 plays a crucial role in cell proliferation and lineage segregation during porcine pre‐implantation embryo development

“…SSEA1 is detected in the ICM of mouse and pig embryos, 13 whereas SSEA3, SSEA4, TRA‐1‐60, TRA‐1‐81 and GCTM‐2 were expressed in ICM of human blastocysts 14 . Furthermore, OCT4 expression in mouse blastocysts is limited to the ICM, whereas OCT4 in porcine and human blastocysts is expressed in both the ICM and TE 15‐17 . In addition, the signalling required for maintaining the pluripotency of mouse ESCs differs from species to species.…”

“… 14 Furthermore, OCT4 expression in mouse blastocysts is limited to the ICM, whereas OCT4 in porcine and human blastocysts is expressed in both the ICM and TE. 15 , 16 , 17 In addition, the signalling required for maintaining the pluripotency of mouse ESCs differs from species to species. While leukaemia inhibitory factor and bone morphogenetic protein 4 signalling play crucial roles in maintaining the pluripotency of mouse ESCs, 18 in humans, ESC pluripotency is maintained through extracellular signal‐regulated kinase and ACTIVIN/NODAL signalling pathways.…”

Associations among morphological parameters, clinical factors and euploid blastocyst formation

“…Other studies have also shown that blastocyst-stage embryo morphology is associated with euploidy, especially concerning ICM and TE parameters (Wang et al, 2016;Barash et al, 2017). The reduced number of TE cells can be attributed to cell division failure due to organelle and chromosomal abnormalities, especially aneuploidy (Iwasawa et al, 2019).…”

Consistency between chromosomal status analysis of biopsied human blastocyst trophectoderm cells and whole blastocyst cells

“…Human blastocysts are constituted by approximately 300 cells; 8 however, to this day, no study has determined the extent to which the 5 biopsied TE cells represent the chromosomal status of the whole blastocyst. As is known, TE cells differentiate into placental tissues after implantation.…”