Recently, the potential detrimental effect that the duration of storage time may have on vitrified samples has raised some concerns, especially when some studies found an association between cryostorage length and decreased clinical results. This study aimed to evaluate the effects of the storage time length of day-5 vitrified blastocysts in 2 study groups: freeze-all cycles and nonelective frozen embryo transfers. This was a retrospective study that included 58,001 vitrified/warmed day-5 blastocysts from 2 different populations, according to the reason for frozen embryo transfer. Elective frozen embryo transfer comprised freeze-all cycles (N=16,615 blastocysts and 16,615 patients) in which only single embryo transfers and only the first frozen embryo transfer were included. The nonelective frozen embryo transfer group included 41,386 embryos from 25,571 patients where frozen embryo transfer took place using supernumerary embryos after fresh embryo transfer. All the possible frozen embryo transfers were included. Both single embryo transfer and double embryo transfers were included. Donor and autologous oocytes were used. The period covered by this study was 11 years. The blastocyst sample was clustered into deciles, which provided specific storage duration categories. The main outcome was the live birth rate, and secondary outcomes were embryo survival, miscarriage, and clinical and ongoing pregnancy rates according to storage duration. The impact of storage time was assessed by univariable analyses in both groups. The comparison was made between each decile and the last one. A multivariable logistic regression analysis was conducted, including the variables with significant association found in the univariate analysis. Student test and chi-square tests, or an analysis of variance, were used wherever appropriate. <.05 was considered statistically significant. There were statistical differences in baseline characteristics of patients included in the study groups. Storage durations ranged from ≤0.67 to ≥4.34 and from ≤1.8 to ≥34.81 months in freeze-all and nonelective frozen embryo transfer, respectively. Embryo survival did not show statistical differences across the categories of storage time in freeze-all and nonelective frozen embryo transfer groups. Statistical differences were found for the live birth rate across some, but not all, the subgroups of storage duration. The multivariable analysis showed no association between storage time and the live birth rate in both groups (nonsignificant). Blastocyst quality, body mass index, number of retrieved oocytes, endometrial preparation, male factor, and uterine factor were related to the drop in the live birth rate in the freeze-all group (<.05). In the nonelective frozen embryo transfer group, the variables that showed significant association with the live birth rate were age at retrieval and frozen embryo transfer, type of frozen embryo transfer (single embryo transfer or double embryo transfers), number of retrieved oocytes, body mass index, endometrial preparation, origin of sperm sample, and female factor. This large study demonstrated no association between storage time and clinical outcome. Other variables, such as the patient’s age, embryo quality, body mass index, and etiology, are somewhat responsible for impacting the outcome. This provides evidence for the safety of embryo vitrification, even after long storage periods. This is reassuring for both in vitro fertilization practitioners and patients undergoing frozen embryo transfer of either elective or nonelective embryos.

中文翻译：

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胚胎长期保存不会影响辅助生殖技术的结果：对 11 年 58,001 个玻璃化囊胚的分析

最近，储存时间的持续时间可能对玻璃化样品产生的潜在有害影响引起了一些担忧，特别是当一些研究发现冷冻储存时间与临床结果下降之间存在关联时。本研究旨在评估 2 个研究组中第 5 天玻璃化胚泡储存时间长度的影响：全冷冻周期和非选择性冷冻胚胎移植。这是一项回顾性研究，根据冷冻胚胎移植的原因，包括来自 2 个不同群体的 58,001 个玻璃化/加热的第 5 天囊胚。选择性冷冻胚胎移植包括冷冻所有周期（N = 16,615 个囊胚和 16,615 名患者），其中仅包括单个胚胎移植和仅第一次冷冻胚胎移植。非选择性冷冻胚胎移植组包括来自 25,571 名患者的 41,386 个胚胎，其中使用新鲜胚胎移植后的多余胚胎进行冷冻胚胎移植。包括所有可能的冷冻胚胎移植。包括单胚胎移植和双胚胎移植。使用供体和自体卵母细胞。本研究涵盖的时间为11年。囊胚样本被分成十分之一，这提供了特定的存储持续时间类别。主要结局是活产率，次要结局是胚胎存活率、流产以及根据储存时间的临床妊娠率和持续妊娠率。通过单变量分析评估两组的储存时间的影响。对每个十分位数和最后一个十分位数进行比较。进行多变量逻辑回归分析，包括单变量分析中发现的具有显着相关性的变量。在适当的情况下使用学生检验和卡方检验或方差分析。 <.05被认为具有统计显着性。研究组中患者的基线特征存在统计学差异。全冷冻胚胎移植和非选择性冷冻胚胎移植的保存时间分别为≤0.67至≥4.34个月和≤1.8至≥34.81个月。在全冷冻和非选择性冷冻胚胎移植组中，不同储存时间类别的胚胎存活率没有显示出统计差异。一些（但不是全部）储存时间亚组的活产率存在统计差异。多变量分析显示两组的储存时间和活产率之间没有关联（不显着）。囊胚质量、体重指数、卵母细胞数量、子宫内膜制备、男性因素和子宫因素与全冷冻组活产率下降有关（<.05）。在非选择性冷冻胚胎移植组中，与活产率显着相关的变量是检索年龄和冷冻胚胎移植年龄，冷冻胚胎移植的类型（单胚胎移植或双胚胎移植）、取出的卵母细胞数量、体重指数、子宫内膜制备、精子样本来源和女性因素。这项大型研究表明储存时间和临床结果之间没有关联。其他变量，例如患者的年龄、胚胎质量、体重指数和病因，也在一定程度上影响结果。这为胚胎玻璃化冷冻的安全性提供了证据，即使在长期储存后也是如此。这对于体外受精从业者和接受选择性或非选择性胚胎冷冻胚胎移植的患者来说都是令人放心的。