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.

最近的研究报道了在辅助生殖技术（ART）中最佳选择胚胎的形态动力学指标。胚泡期的形态动力学包括解冻后的崩塌和再扩张速率。但是，尚未建立使用这些形态动力学的评估方法，主要是因为尚不清楚潜在的分子机制。在这项研究中，我们集中在囊胚行为的这些形态动力学观察与构成囊胚的细胞数量之间的关系。我们使用延时摄影技术评估了38个多余的人类冻融胚泡，并记录了它们的膨胀，收缩和孵化。共有28个胚泡中培养（横截面面积≥5000π微米扩大²）。与未发育组相比，扩展组的内细胞团（ICM）和滋养外胚层（TE）细胞数量显着增加，最终分别发育为胎儿和胎盘（ICM：与未分化的相比，扩展了10.2±6.3。 -扩展6.0±12.3，p <0.05； TE：扩展165.7±74.8与非扩展57.0±29.4，p <0.05）。此外，在扩增速率（至4 h）与TE细胞数量之间存在正相关（r = 0.558，p = 0.0021）。此外，孵出的胚泡比未孵化的胚泡具有更高的TE细胞数量（孵化225.2±61.2与未孵化121.1±48.6，p<0.0001）。每单位截面积的TE细胞数量与收缩时间负相关（r = –0.601，p = 0.0007）。没有检测到ICM细胞的数量和这些形态动力学之间的相关性。总之，我们的研究表明，冷冻解冻的胚泡的不同形态动力学反映了TE细胞的数量。含有足够TE细胞的胚泡的分化对于随后的妊娠的植入和预后将是有益的。因此，评估这些形态动力学可以是一种有效的方法，可以筛选出良好的胚胎进行抗逆转录病毒疗法。