['To evaluate the clinical significance of the grey zone range (50-59%) of the hypo-osmotic swelling test (HOST) on sperm samples.', 'Clinical and viable pregnancy rates and implantantion rates following in vitro fertilization-embryo transfer (IVF-ET) were determined in couples where the male partner scored between 50-59% on the HOST. The data were further evaluated according to the discrepancy between viability and HOST. Finally, the study assigned whether treating sperm with the protein digestive enzyme chymotrypsin had any effect on pregnancy outcome.', 'Pregnancy and implantation rates were comparable for couples with grey zone HOST scores with the normal IVF rate for the center. Having a large discrepancy between viability and HOST scores had no clinical significance nor did treatment with chymotrypsin.'] Is grey zone score for hypo-osmotic swelling test ( HOST ) associated with embryo implantation defects?