P-239 Comparative study between two commercial vitrification kits on survival and clinical outcome for blastocyst frozen embryo transfer

Study question

To compare the post thaw survival and clinical outcome of blastocyst (D5/D6) transfer between two different commercially available kits for freezing and thawing.

Summary answer

There is significant difference on survival of post thaw blastocyst and clinical outcomes between Kitazato (Japan) and Irvine (USA) vitrification media.

What is known already

Vitrification is widely used in embryo preservation for its reliable outcome and the ease of use. Different brands of commercial freezing and thawing kits are available. The main difference between the two commercial vitrification kits used in this study are the different extracellur cryoprotectant used in which Kitazato contain trehalose supplemented with hydroxypropyl cellulose while Irvine contain sucrose with dextran serum supplement. Recent study suggested that cell apoptosis in specimen vitrified in trehalose media is lower in comparison to sucrose.

Study design, size, duration

Retrospective study was carried out from 2022-2023. Patient with uterine abnormalities, history of recurrent implantation failure (RIF), patient that underwent Preimplantation Genetic Testing (PGT) and those transferring D2/3 embryo were excluded. Survivability of post thaw blastocyst and clinical outcome of frozen blastocyst transfer were compared between Kitazato (N = 374) and Irvine (N = 253) vitrification kit. The data was analyzed using t-test and Anova.

Participants/materials, setting, methods

Blastocysts that were vitrified and warmed with vitrification kit from the same manufacturer were grouped together and compared. Patient in each vitrification arms were divided into two main age groups which are <37 years old and ≥37 years old. The survivability and clinical outcome of the two respective vitrification kits was compared between the age group, blastocyst grading prior to freezing (Good, Fair, Poor) and the day of blastocyst freezing (D5 or D6).

Main results and the role of chance

The overall mean post thawed survival was higher in Kitazato (95.8%) compare to Irvine (91.8%) (p < 0.001). In patient age <37 years old, Kitazato group performed better when compare to Irvine group. Post thawed survival using Kitazato warming was significantly better (p < 0.001) on good (AA,AB,BA) and fair graded (BB) blastocyst with mean survival of 97.1% vs 93.4% and 94.9% vs 87.6% respectively. Similarly, post thawed survival of D5 and D6 blastocysts were significantly higher in Kitazato group when compared to Irvine group with mean survival of 96.7% vs 92.8% and 94.8% vs 90.3% respectively. However no significant difference was observed in post thawed survival outcome for patient aged ≥ 37 years old between both groups in the same study parameters.

In terms of clinical outcomes, there is also no difference observed between Kitazato group and Irvine group on beta hCG positive rates.

Interestingly, the Irvine group shown to have significantly higher clinical pregnancy compare to Kitazato group (53% vs 60% respectively) but no significant difference was observed in sub group for patient aged < 37 years old and ≥ 37 years old. Furthermore, the implantation rate (IR) in Irvine group group (55.7%) is also significantly higher compare to the Kitazato group (50.5%).

Limitations, reasons for caution

Potential confounder factors such as stimulation protocol and the embryologist experience were not factored in may have affected the outcome of the study. Sample size can be increased to improve confidence in this study.

Wider implications of the findings

This study demonstrates that the post thaw survivability is better in the Kitazato group while the clinical outcome is better in the Irvine group. Thus this can give a better understanding of the respective commercial vitrification kits and provide insight for laboratories to choose for their clinical practices.

Trial registration number

Not Applicable