HYPOOSMOTIC SWELLING CAN ACCURATELY ASSESS THE VIABILITY OF NONMOTILESPERM

Viable, healthy sperm are preferred for oocyte fertilization with intr acytoplasmic sperm injection. Currently, motility is the most widely a pplied measure of sperm viability. However, with this criterion, viabl e but immotile sperm are overlooked as candidates for micromanipulatio n. Supravital stains identify viable sperm but may be toxic to the gam ete or embryo. We tested the hypothesis that hypo-osmotic swelling, de veloped to assess sperm membrane integrity, can accurately determine s perm viability. Thawed sperm from 12 fertile donors were exposed to a hypo-osmotic solution and to two supravital stains. A total of 2,010 s perm were assessed for tail coiling after a 30-min exposure to hypo-os motic solution. By supravital stains, 31% of thawed sperm were viable; 23% showed tail coiling. Among coiled-tail sperm, 100% were viable by supravital stain. As a measure of viability, tail coiling exhibited a sensitivity of 30%, specificity of 100%, and positive predictive valu e of 100% compared to supravital stains. With a 60-min hypo-osmotic in cubation, the specificity (89%) and positive predictive value (78%) de creased significantly (P < 0.05). Therefore, hypo-osmotic swelling acc urately detects viable sperm among a nonmotile population. Assay accur acy, however, is very sensitive to the incubation time in hypoosmotic solution. (C) 1997 Wiley-Liss, Inc.