P-048 Vitrification of human semen impairs the mobility of spermatozoa when compared to the conventional slow-freezing
Authors: Pungert T , Podgrajsek R , Stimpfel M , Rugelj B , Drobnic S , Ban-Frangez H 
Published: June 2023

Study question

Does vitrification provide a better method for human sperm cryopreservation than slow freezing in terms of survival, mobility, maturity, and DNA fragmentation?

Summary answer

Vitrification of human semen yields similar outcome as slow-freezing considering survival, mobility, DNA fragmentation, and maturity but the mobility after thawing is lower.

What is known already

Slow freezing is the most common technique for cryopreservation of human sperm. Unfortunately, many sperm cells die during the process or lose their mobility and are thereafter unable of fertilization. Meanwhile, vitrification of animal sperm showed good outcomes in terms of sperm survival and motility while being easier to perform than slow freezing. So far, many studies focused on survival and mobility of human sperm after vitrification compared to slow freezing, with results still not unified. They also neglected the importance of sperm maturity and DNA fragmentation caused by the process. DNA damage can affect embryo development or cause abortion.

Study design, size, duration

The study was performed from March January to July 2022. It included 69 male participants who underwent a diagnostic spermiogram at the Division of gynaecology and obstetrics of University Medical Centre Ljubljana. All participants gave written consent of using the remaining of sample, after performing the spermiogram, for our study. Sperm samples were divided in three aliquots, one saved as native sample, one intended for vitrification, and one intended for slow freezing.

Participants/materials, setting, methods

Participants in the study had normal sperm quality parameters according to 5th edition of WHO manual. Slow freezing was performed using Sperm Freezing medium (Origio). For vitrification sperm was diluted in solution consisting of Sperm preparation medium (Origio), sucrose, and HSA in 1:1 (v/v) ratio, incubated for five minutes and then vitrified by adding 30 microliter droplets directly into liquid nitrogen. After thawing sperm survival, mobility, maturity, and DNA fragmentation were assessed.

Main results and the role of chance

The data are presented as mean values (± standard deviation) when normally distributed and as medians (IQR) when not normally distributed. The patient’s age was 35.0±5.1 years. In native sperm sample, sperm concentration was 69.6±59.0x106 cells per millilitre and total motility was assessed to be 60.0% (50.0%-70.0%). After thawing we noticed significantly lower mobility (p &lt; 0.001), while also the mobility was significantly lower after vitrification when compared to slow-freezing (17.6% (12.4%-25.3%) and 14.5% (9.0%-22.6%), p = 0.007). Interestingly, there was no difference in survival after thawing the samples (20.5±10.7 % after slow freezing and 23.7±13.7 % after vitrification). Also there was no difference in maturity of sperm when checked with protamine staining (native vs. slow-freezing vs. vitrification; 53.6±15.2 % vs. 53.9±16.0 % vs. 52.4±15.2 %, p = 0.905) and also when checked with hyaluronan binding assay (78.0% (67.5%-82.4%) vs. 79.4% (71.7%-82.95%) vs. 75.3% (67.5%-81.1%), p = 0.607) . While sperm maturity was not affected with cryopreservation, DNA fragmentation was significantly higher after cryopreservation (native vs. slow-freezing vs. vitrification; 19.7±9.5%, vs. 24.7±11.6 vs. 27.1±15. %, p = 0.049).

Limitations, reasons for caution

We believe our study would be better by obtaining higher number of participants and by being performed over longer time period. We would also like to further optimise vitrification protocol. More knowledge is also needed in poor sperm samples, since we only included sperm samples of good quality.

Wider implications of the findings

We believe our finding are of great importance for the field of andrology. Our results show vitrification of human sperm can be comparable to slow freezing in most of parameters analysed, but lower mobility after vitrification is reason for caution.

Trial registration number

20210024