Abstract
BackgroundIn the absence of international guidelines indicating the usage of vitrification rather than slow-freezing, the study aim was to analyze a large cohort of slow-frozen/thawed embryos to produce a rationale supporting the standardization of IVF cryopreservation policy.MethodsThis retrospective analysis included 4779 cleavage stage embryos cryopreserved by slow-freezing/thawing from September 2009 to April 2017 at a single Center. Biological and clinical outcomes of three different commercial kits adopted sequentially, i.e. Vitrolife Cleave Kit® from Vitrolife (kit 1) vs. K-SICS-5000 Kit® and K-SITS-5000 Kit® from Cook Medical (kit 2) and Freeze/Thaw 1™ Kit® from Vitrolife (kit 3) were collected and compared in the light of cryoprotectants composition.ResultsKit 3 compared to kit 1 and kit 2 showed significantly (P < 0.001) higher embryo survival (79.9% vs. 75.6 and 68.1%, respectively) and frozen embryo replacement (91.5% vs. 86.5 and 83.3%, respectively) rates, and significantly (P < 0.001) lower blastomere degeneration rate (41.5% vs. 43.6 and 52.4%, respectively). No significant difference for clinical outcomes was observed among kits. Only a slight positive trend was observed for kit 3 vs. kit 1 and kit 2 on delivery rate per thawing cycle (7.12% vs. 4.19 and 4.51%, respectively; P < 0.058) and live birth rate (3.07% vs. 2.59 and 1.93%, respectively, P < 0.069). Thawing solutions of kit 3 were similar to those of any warming protocol.ConclusionsA defined concentration of extracellular cryoprotectants in thawing/warming solutions had a beneficial effect on the embryo cryosurvival rate. Results could provide the rationale for the adoption of a single standardized warming protocol.
Highlights
In the absence of international guidelines indicating the usage of vitrification rather than slowfreezing, the study aim was to analyze a large cohort of slow-frozen/thawed embryos to produce a rationale supporting the standardization of in vitro fertilization (IVF) cryopreservation policy
It is acknowledged that vitrification is superior to slow-freezing with a moderate quality of evidence regarding oocyte and embryo cryosurvival rates, but it is known that the quality of evidence regarding clinical outcomes remains low by comparing the two methods [23]
From September 2009 to December 2010, a total of 618 cleavage stage embryos were obtained from 288 patients and slowfrozen/thawed with kit 1; from January 2011 to April 2015, a total of 2856 cleavage stage embryos were obtained from 916 patients and slow-frozen/thawed with kit 2; from May 2015 to April 2017, a total of 518 cleavage stage embryos were obtained from 418 patients and slow-frozen/thawed with kit 3
Summary
In the absence of international guidelines indicating the usage of vitrification rather than slowfreezing, the study aim was to analyze a large cohort of slow-frozen/thawed embryos to produce a rationale supporting the standardization of IVF cryopreservation policy. During embryo cryopreservation, the formation of intracellular ice can lead to cell damage and development arrest with a negative impact on cryosurvival ability [1,2,3] To overcome these problems, in the last thirty-years there has According to this definition, in 2016 the annual report from the Italian IVF National Registry reported that the Capodanno et al Reproductive Biology and Endocrinology (2019) 17:84. Slowfreezing was the first cryopreservation method developed and leading to the first FER pregnancy [12] It was used until the vitrification method has progressively replaced it at many IVF Centers worldwide [13,14,15,16] on the basis of several data reporting higher cryosurvival and blastulation rates [17,18,19,20,21,22]. It is acknowledged that vitrification is superior to slow-freezing with a moderate quality of evidence regarding oocyte and embryo cryosurvival rates, but it is known that the quality of evidence regarding clinical outcomes remains low by comparing the two methods [23]
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