P-140 A retrospective study on combination of vitrification/warming protocols from different manufacturers
Authors: Salimov D , Kazakova I , Mayasina E , Buev Y , Lisovskaya T 
Published: June 2022

Abstract

Study question
What is the embryo survival rate when combining freezing and warming media from different manufacturers.

Summary answer
Vitrification protocol with DMSO in freezing medium and 4-step warming at room temperature resulted in highest implantation and high embryo survival rates.

What is known already
Cryopreservation media containing 7,5% and 15% DMSO in a two-steps protocol are widely used for vitrification of human embryos. Studies with the data on safety, survival rates, cellular structures integrity and the warmed embryo's implantation potential confirm efficiency of DMSO as cryoprotectant. However, questions remain on whether DMSO have any negative impact, thus interest to DC. Likewise with the choice of cryoprotectant, more data is needed to determine which temperature corresponds to better survival rates.

Study design, size, duration
This retrospective cohort study covered the period from January 2019 till November 2021. A total of 834 consecutive cycles of frozen/warmed embryo transfers were included in the study. Inclusion criteria were: women's age below 40 years, cryopreservation on the day 5 of embryo culture. Exclusion criteria were: donor oocyte cycles, cycles with pre-implantation genetic testing for aneuploidies and cycles with severe male factor after surgical sperm retrieval.

Participants/materials, setting, methods
Following groups were compared using Rapid-i carrier device: 1 - Kitazato vitrification/warming protocol, 2 - Kitazato vitrification and Vitrolife's Omni warming, 3 - Vitrolife's Omni vitrification/warming, 4 - Vitrolife's Omni vitrification and Kitazato warming, 5 - Kitazato vitrification/Vitrolife's Omni warming media used in accordance with Kitazato protocol (ambient temperature, Reproplate dish). Efficiency was evaluated comparing embryo survival, implantation, clinical pregnancy and early pregnancy termination rates. Mann-Whitney and Pearson's Chi-square tests were used for statistical analysis.

Main results and the role of chance
The average patient age in assigned groups was: group 1: 32,5±3,6 years (n = 569); 2:32,2±3,5 years (n = 47); 3:30,4±3,5 years (n = 15); 4:32,3±3,5 years (n = 74); 5:32,7±3,4 years (n = 129). Average number of transferred embryos: 1,3±0,5; 1,2±0,4; 1,1±0,3; 1,3±0,4 and 1,2±0,4 per group, respectively. Embryo survival rates were: 97%, 96%, 100%, 97% and 100% in each group, respectively. Group 5 was significantly different from other groups (p &lt; 0,05; group 3 had too small sample size for an adequate comparison). Implantation rates per group: 43%, 57%, 44%, 40% and 49%, respectively (p &gt; 0,05). Clinical pregnancy rates were not different between groups. The early pregnancy termination rates were: 18,1%, 20,7%, 33,3%, 14,7% and 8,9% per group, respectively (p &gt; 0,05). Therefore, group 2 resulted in a best clinical outcomes.

Limitations, reasons for caution
The present study is a retrospective cohort study and it has a limited number of patients in compared groups. Additionally, live births and health of newborn children was not taken into account.

Wider implications of the findings
Freezing medium from one manufacturer can be combined with warming medium from another manufacturer and result in a good clinical outcome. Furthermore, this study sheds the light that there is still a room for the improvement of existing cryopreservation media and protocols.

Trial registration number
not applicable