Abstract
Study question
Are there any advantages in using High security tubes rather than High Security straws for conventional slow sperm freezing?
Summary answer
Freezing sperm in High Security tubes (HST) improved post-thaw recovery rate and motility, and also reduced processing and handling compared to High Security straws (HSS).
What is known already
The use of High Security freezing consumables (HSFC) in an IVF setting is a safe and effective way of eliminating concerns related to viral cross-contamination during storage. The lower diameter of HSS does make them susceptible to warming during handling. The HSFC used in this study is the only CE marked products that are made of resin, leak-proof and shatter-proof in all cryogenic temperatures even in LN2. No previous studies have compared the use of HST with HSS for conventional human sperm freezing. This study sets out to investigate the performance of HST compared to HSS.
Study design, size, duration
The study was designed as a controlled split-sample study with blind post-thaw analysis. Following the routine WHO analysis of 20 semen samples, the remainder of each of the samples was evenly divided and cryopreserved by conventional slow freezing in each of the two different HSFC. The freeze was conducted simultaneously by the same practitioner, employing the same freezing protocol and cryoprotectant. The pre-freeze and post-thaw concentration, total and progressive sperm motility were recorded.
Participants/materials, setting, methods
At one IVF clinic, semen samples with sperm density ≥15million/ml, ≥40% motility, ≥1.5ml were included. Cryoprotectant (SpermFreeze, Fertipro) was added dropwise to unprepared semen and kept at room temperature for 10 minutes before loading into HSFC (0.5ml CBS™HSS; CBS™HST). HSFC were heat-sealed (SYMS; SYMSIII sealers) and placed in vapour for 30 minutes before plunging into LN2. Samples were thawed by immersion in a 37Cº water bath for 5 minutes and analysed using WHO methods.
Main results and the role of chance
Paired-t test was used to compare the percentage motility between the different HSFC. All analysis was considered statistically significant when p < 0.01.
We demonstrated that the sperm recovery rate (Percentage total motility post-thaw/ Percentage total motility pre-freeze) in HST was 66.63 ± 14.94 (mean ± standard deviation) compared to 40.80 ± 14.69 in HSS.
In the HSS, the percentage post-thaw total motility was 19.99 ± 7.21 and the percentage post-thaw progressive motility was 12.26 ± 2.59. In the HST, the percentage post-thaw total motility was 32.57 ± 8.33 and the percentage post-thaw progressive motility was 23.08 ± 5.53. The overall improvement when using HST against HSS was 12.53 ± 5.69, 10.44 ± 5.29 for the total motility and the progressive motility respectively.
Comments were recorded regarding the handling and the condition of the HSS and HST for each freeze event. Neither device displayed any leakage of LN2 or any explosion during the warming. The freezing process was easier and faster using HST rather than HSS. It was also noted that the entire sample can be recovered from the HST, unlike the HSS.
Limitations, reasons for caution
The study looked at sperm recovery in terms of motility only. DNA damage was not considered as a parameter of sperm quality. Also, fertilization, pregnancy rates, live birth rates and the use of poorer quality sperm samples have not been investigated.
Wider implications of the findings: For conventional sperm freezing, the use of HST resulted in improved sperm motility and progression post-thaw, when compared to HSS. This finding supports the use of HST to improve the post thaw quality of sperm, benefitting patients with own frozen samples, recipients of donor sperm and donor sperm banks.
Trial registration number
Not applicable.
Numerical Modeling of Sperm Swimming