Blastocysts hatch from the zona pellucida (ZP) to enable implantation into the uterine endometrial epithelium, but little is known regarding the effect of hatching sites on pregnancy outcomes. Murine hatching embryos were categorized into five groups based on initial trophectoderm projection (TEP)/ZP position corresponding to the inner cell mass center. In blastocysts (3.5 dpc) post-12 hours in vitro culture, TEP rates of A-site (44.4%) and B-site (38.6%) embryos were higher than those of C-site (12.5%) and D-site (3.1%) embryos, while the O-site (1.4%) was the lowest (P < .05). Post-ET A-site (55.6%) and B-site (65.6%) birth rates were higher than those of C-site embryos (21.3%) and controls (P < .05). Furthermore, live birth rate of B-site embryos remained higher than C-site embryos (68.8% vs 31.3%; P < .05) when both were transferred into the same recipients. Different TEP site blastocysts exhibited different implantation competences: the implantation rate of C-site embryos was lower than that of both A- and B-site groups (67.7% vs 84.3% and 83.2%, respectively; P < .05) at 2 days post-ET. C-site embryos also had a distinctly higher ratio of developmental defects (47.5%) than A- and B-site embryos (22.5% and 14.6%, respectively), with implantation failure mainly associated with poor birth rate, a finding corroborated by differential gene expression analysis such as LIF, LIFR, and S100a9. Surprisingly, acidified Tyrode's solution (AAH)-treated B-site blastocysts had a significantly increased birth rate (77.1%) than C-site (55.3%) and controls (43.4%). Site specificity and differential gene expression during embryo hatching can be applied in ART screening. More importantly, assisted hatching by AAH is effective and feasible for improving pregnancy and term development, particularly at the B-site, for humans and in animal husbandry.

中文翻译：

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囊胚孵化的位点特异性显着影响小鼠的妊娠结局

囊胚从透明带 (ZP) 孵化以植入子宫内膜上皮，但关于孵化部位对妊娠结局的影响知之甚少。根据对应于内细胞团中心的初始滋养外胚层投影 (TEP)/ZP 位置，将小鼠孵化胚胎分为五组。在体外培养12小时后的囊胚（3.5 dpc）中，A位（44.4%）和B位（38.6%）胚胎的TEP率高于C位（12.5%）和D位（ 3.1%) 胚胎，而 O 位点 (1.4%) 是最低的 ( P  < .05)。ET 后 A 位（55.6%）和 B 位（65.6%）出生率高于 C 位胚胎（21.3%）和对照（P < .05）。此外， 当两者被转移到相同的受体时，B 位胚胎的活产率仍然高于 C 位胚胎（68.8% 对 31.3%；P < .05）。不同TEP位点囊胚表现出不同的着床能力：C位胚胎的着床率低于A位组和B位组（分别为67.7% vs 84.3%和83.2%；P < .05) 在 ET 后 2 天。C 位胚胎的发育缺陷率（47.5%）也明显高于 A 位和 B 位胚胎（分别为 22.5% 和 14.6%），植入失败主要与低出生率有关，这一发现得到了差异化的证实基因表达分析，如 LIF、LIFR 和 S100a9。令人惊讶的是，酸化的 Tyrode 溶液 (AAH) 处理的 B 位囊胚的出生率 (77.1%) 比 C 位 (55.3%) 和对照 (43.4%) 显着增加。胚胎孵化期间的位点特异性和差异基因表达可用于 ART 筛选。更重要的是，AAH 辅助孵化对于改善妊娠和足月发育是有效且可行的，尤其是在人类和畜牧业的 B 位点。