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Updated: Aug 3, 2025
Morphometric Protocol for the Objective Assessment of Blastocyst Behavior During Vitrification and Warming Steps
Published on: February 28, 2019
An all-37 °C thawing method improves the clinical outcomes of vitrified frozen-thawed embryo transfer: a
Gaofeng Yan1, Youlin Yao1, Wenjuan Yang1
1Department of Reproduction and Genetics, First Affiliated Hospital of Kunming Medical University, Kunming, 650032, Yunnan, China.
Purpose:
The purpose of this study is to assess the impact of different temperatures and incubation times on the clinical outcomes of FET cycles during the thawing procedure and to select a better thawing method to improve clinical outcomes.
Methods:
This retrospective study included 1734 FET cycles from January 1, 2020, to January 30, 2022. Embryos vitrified using a KITAZATO Vitrification Kit were thawed at 37 °C in all steps (the case group, denoted the "all-37 °C" group) or at 37 °C and then at room temperature (RT; the control group, denoted the "37 °C-RT" group), according to the kit instructions. The groups were matched 1:1 to avoid confounding.
Results:
After case-control matching, 366 all-37 °C cycles and 366 37 °C-RT cycles were included. The baseline characteristics were similar (all P > 0.05) between the two groups after matching. FET of the all-37 °C group yielded a higher clinical pregnancy rate (CPR; P = 0.009) and implantation rate (IR; P = 0.019) than FET of the 37 °C-RT group. For blastocyst transfers, the CPR (P = 0.019) and IR (P = 0.025) were significantly higher in the all-37 °C group than in the 37 °C-RT group. For D3-embryo transfers, the CPR and IR were non-significantly higher in the all-37 °C group than in the 37 °C-RT group (P > 0.05).
Conclusions:
Thawing vitrified embryos at 37 °C in all steps with shortening wash time can enhance CPR and IR in FET cycles. Well-designed prospective studies are warranted to further evaluate the efficacy and safety of the all-37 °C thawing method.
