Comparison of different freezing methods for micro-volume semen

BACKGROUND: Mico-volume semen freezing is essential and used popularly for fertility preservation of patients suffering cancer or undergoing male reproductive system related surgeries, and for other reasons that may risk fertility potential in ART cycles. However, clinicians and embryologists still face some unresolved technical and theoretical issues about the frozen-thawed efficiency. OBJECTIVE: To choose the appropriate freezing method for different volumes of normal semen samples. MATERIALS AND METHODS: We investigated the frozen-thawed outcomes of semen with different volumes (20 μL, 50 μL, 100 μL, 200 ??L, 500 μL and 1 mL) using two freezing methods (FLNV, static liquid nitrogen vapour cooling followed by liquid nitrogen preservation; RFLN, direct rapid freezing in liquid nitrogen) and analyzed the vitality, progressive motility and DNA fragmentation index of thawed sperm. RESULTS: We found that semen freezing with volumes more than 100 μL had better outcomes than volumes less than or equal to 50 μL after thawing. FLNV presented a higher efficiency for cryopreservation of semen with volumes less than 50 μL. CONCLUSION: For smaller (micro) volumes, the FLNV technique is better than the RFLN method.