Comparison of effects of thawing entire donor sperm vial vs. partial thawing (shaving) on sperm quality

Purpose: Partial thawing of a vial of cryopreserved sperm (shaving) is sometimes applied as a measure to preserve sperm for further use, particularly in cases of very restricted sperm quantity. However, mechanical violence may disrupt the sperm-wall and lead to impaired in-vitro fertilization (IVF) outcomes. Material and methods: In a retrospective case-control study at a tertiary, university-affiliated medical center, we compared the IVF/intracytoplasmic sperm injection (ICSI) outcomes of patients who used donor sperm following partial thawing (shaving) of the vial of cryopreserved sperm (n = 99) to a control group consisting of patients for whom the vial of sperm was completely thawed before use (n = 99). Results: While no differences were observed in the rates of oocyte fertilization, the mean number of top-quality embryos (TQE) was significantly lower in the shaving group than in the complete thawing group (1.33 ± 0.17 vs. 1.87 ± 0.17, p < 0.02). Experimental analysis of aliquots from the same donors revealed significantly reduced motility in sperm samples that were shaved vs. fully thawed (6.5 vs. 37.1%, p < 0.001). Conclusions: In cases in which available cryopreserved sperm samples are limited, shaving of the vial without thawing can be used but with caution and only when absolutely necessary. Further, large prospective studies are needed to better clarify whether there is post-thawing sperm damage and to compare IVF outcomes after these two thawing methods.