Post-warming embryo morphology is associated with live birth: a cohort study of single vitrified-warmed blastocyst transfer cycles

Meagan Allen,Catharyn Stern,Daniel Lantsberg,Lyndon Hale,Violet Kieu,Yossi Mizrachi,John Stevens,David K Gardner

doi:10.1007/s10815-021-02390-z

Meagan Allen, Catharyn Stern + Show 6 more

Open Access

https://doi.org/10.1007/s10815-021-02390-z

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Abstract

PurposeThis study aims to examine whether blastocyst morphology post-warming correlates with live birth.MethodsIn this cohort study, morphological characteristics post-warming were reviewed in all single vitrified-warmed blastocyst transfer cycles performed between November 2016 and May 2017. Immediately before transfer, the degree of blastocoel re-expansion was graded as A, fully expanded; B, partially expanded ≥ 50%; C, partially expanded < 50%; and D, collapsed. The degree of post-warming cell survival was graded on a scale of 50 to 100% and was then classified into 4 groups: very low 50–70%, low 71–80%, moderate 81–90%, and high 91–100%.ResultsOverall, 612 cycles were reviewed, of which 196 included PGT-A tested embryos. The live birth rate (LBR) increased from 11.4% in the collapsed blastocysts group to 38.9% in the post-warming full re-expansion group (p < 0.001) and from 6.5% for blastocysts with a very low cell survival rate to 34.7% for blastocysts with high cell survival rate (p = 0.001). LBR was 6.7% for blastocysts with the worst post-warming morphological characteristics, namely, collapsed with very low cell survival rate. On multivariate analyses, partial blastocyst re-expansion ≥ 50%, full re-expansion, and high cell survival rate remained significantly associated with live birth, after controlling for female age, pre-vitrification morphological grading, and PGT-A. A sub-analysis of cycles using PGT-A tested embryos showed similar results.ConclusionPost-warming re-expansion and high cell survival rate are associated with higher LBR in euploid and untested blastocysts. However, embryos with poor post-warming morphology still demonstrate a considerable probability of live birth, and they should not be discarded.

Highlights

The utilization of frozen embryos in assisted reproductive technology (ART) has increased substantially over the last decade [1, 2]
In light of the limited evidence and conflicting results, we deem a need for a large study of single blastocyst transfer cycles in order to examine the value of post-warming embryo morphology in untested and euploid embryos. In this cohort study of single vitrified blastocyst transfer cycles, we examined whether embryonal post-warming characteristics correlated with live birth
We found that post-warming blastocyst characteristics correlated with cycle outcome

Summary

Introduction

The utilization of frozen embryos in assisted reproductive technology (ART) has increased substantially over the last decade [1, 2]. The major forces behind this trend are improved embryo survival with vitrification method, the policy of single-embryo transfer employed in some clinics, the use of preimplantation genetic testing, and the use of freeze-all strategy for various indications [3]. Vitrification and warming pose great challenges to the embryo. Dehydration and rehydration might cause cellular damage. The large volume of fluid contained in the blastocoel cavity exposes it to a potential risk of structural damage due to the formation of ice crystals, though to a lesser extent when using vitrification as compared with slow freezing. Most vitrified embryos will survive the vitrification-warming process. It has been shown that between 1 and 5% of vitrified blastocysts may fail to survive after warming [4, 5]

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