Improvement in motion characteristics and acrosome status in cryopreserved human spermatozoa by swim-up processing before freezing

The purpose of this study was to examine if selecting a sperm population with improved motion characteristics before freezing reduces the deleterious effects of cryopreservation. Semen specimens from 15 normal donors were divided into two equal aliquots. The first aliquot received no treatment (control), and the second was processed by swim-up from a washed sperm preparation to select a sperm population with better motility and motion characteristics (swim-up). Both aliquots were cryopreserved by the liquid nitrogen vapour method. Percentage motility and motion characteristics were evaluated by computer-assisted semen analysis. Acrosome integrity as well as spontaneous and calcium ionophore-induced acrosome reactions before freezing and after thawing were assessed by fluorescein isothiocyanate conjugated peanut agglutinin combined with a supra vital dye (Hoechst-33258). Swim-up processing enabled selection of a sperm population with better motion characteristics, percentage motility and viability before freezing (P < 0.001), but with no difference in percentage of acrosome-intact spermatozoa (P = 0.63). After thawing, the swim-up specimens exhibited faster velocity and progression than untreated specimens (P < 0.001). They also had higher percentages of spermatozoa with intact acrosomes and spermatozoa able to undergo acrosome reaction in response to calcium ionophore (P < 0.05). Selecting a highly motile sperm population before freezing enhances overall post-thaw spermatozoa quality.