Purpose : To ascertain whether washing sperm from oligozoospermic and normozoospermic samples before cryopreservation improves post-thaw vitality. Methods : Normozoospermic (n = 18) and oligozoospermic (n = 16) samples were divided into three aliquots. The first aliquot remained untreated and the second and third aliquots were subjected to the swim-up and discontinuous density gradient sperm washing techniques respectively. Vitality staining was performed, samples mixed with cryopreservation media and frozen. Spermatozoa were thawed, stained, and vitality quantified and expressed as the percentage of live spermatozoa present. Results : Post-thaw vitality in untreated aliquots from normozoospermic samples (24.9% ± 2.3; mean ± SEM) was significantly higher (unpaired t-tests; P < 0.01) than untreated oligozoospermic samples (11.9% ± 2.3). Post-thaw vitality was significantly higher after swim-up in normozoospermic samples (35.6% ± 2.1; P < 0.001; one-way ANOVA) and oligozoospermic samples (27.7% ± 1.7; P < 0.01). Density gradient centrifugation significantly improved postthaw vitality in oligozoospermic (22.4% ± 1.0; P < 0.01) but not normozoospermic (30.8% ± 1.8) samples. Conclusions : Sperm vitality in cryopreserved oligozoospermic samples was improved by both the swim-up and density gradient centrifugation washing techniques prior to freezing.

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