P-153 Optimizing clinical outcomes in single vitrified-thawed blastocyst transfer cycles: impact of blastocyst re-expansion status
Authors: Kheddache S , Boucekkine N , Oumeziane A , Djerroudib K , Aitchallal N , Zenati F , Benabdelouahed T 
Published: July 2024

Abstract

Study question
is the blastocyst re-expansion status according to the thawing-transfer time interval related to the clinical outcomes in a single frozen-thawed blastocyst transfer cycles?

Summary answer
The post-thawing blastocyst shrinkage is linked to lower clinical outcomes, and minimizing the time between thawing and transfer optimizes outcomes especially for shrunken blastocysts.

What is known already
• A reduced ART outcome was observed with the use of shrunken post-warming blastocysts (Ito et al., 2023)
• The spontaneous blastocyst shrinkage observed during in vitro embryonic development is considered as a negative prognosis factor for implantation (Sciorio et al., 2020)
• The blastocyst’s re-expansion level after thawing proves to be the best post-thaw parameter for the prediction of live birth (The Vienna consensus., 2017. Ahlstrom et al., 2013).
• The fast blastocele re-expansion seems to have a predictive value for implantation in frozen-thawed blastocyst transfer cycle (Shu et al., 2009).

Study design, size, duration
This was a retrospective study of 577 single frozen-thawed blastocyst transfer cycles from January 2022 to April 2023.

Participants/materials, setting, methods
Only B4 and B5 blastocyst quality obtained in day-5 were included in this study.
The morphological characteristics were evaluated: after thawing (T0) and at Transfer time (TR). Blastocysts with 50% reduction of blastocele were classified “Shrunken”, the rest are “re-expanded”. and categorized into Group-1: re-expanded at T0 (n = 173); Group-2: shrunken at T0 and re-expanded at TR (n = 135); Group-3: shrunken at T0 and TR (n = 199).
Statistical tests: chi-square, T-test and Mann-Whitney. (Statistical significance p &lt; 0.05*).

Main results and the role of chance
Clinical outcomes of re-expanded blastocysts comparing to shrunken blastocysts at TR were respectively 42.21% versus 32.71% for pregnancy rate (PR) (p &lt; 0.007),39.61% versus 30.48% for implantation rate (IR) (p &lt; 0.02) and 35.71% versus 22.30% for life birth rate (LBR) (p &lt; 0.004), a significantly higher outcomes were observed for re-expanded blastocysts.
The miscarriage rate decreased from 25.00% to 9.23% (p &lt; 0.001).
The transfer of shrunken blastocysts in an interval of time within 1 hour or less comparing to more than 1 hour between T0 and TR showed the following results: PR = 40.82% versus 28.07% (p &lt; 0.032), IR = 39.81% to 25.10%, (p &lt; 0.02) and LBR = 26.53% versus 19.88% (p &lt; 0.2). a significantly higher clinical outcomes were observed for shrunken blastocysts transferred within 1 hour or less.
Group analysis: the PR, IR and LBR significantly increased for Group-1 comparing to Group 2. For Group-3, shrunken blastocysts at TR had the lower outcomes. (respectively p = 0.003; 0.017; 0.0002)

Limitations, reasons for caution
It is an ongoing retrospective observational study.
Blastocysts with a low quality (B3 or less) were excluded from this study how limit our ability to extend the findings to low morphology degrees not covered by this research.

Wider implications of the findings
The management of frozen blastocyst transfers in IVF laboratories have to take into consideration in addition to the classic morphological evaluation, the blastocoele re-expansion state and the time interval between thawing and transfer to optimize the transfer outcomes.

Trial registration number
not applicable