Use of human zonae from cryopreserved oocytes in a test to assess the binding capacity of human spermatozoa.

Aged unfertilized oocytes from an assisted conception programme were cryopreserved and then utilized after thawing in a zona-binding assay. Oocytes frozen using dimethyl sulphoxide (DMSO) showed poor survival post-thaw (2/40, 5%) compared to those frozen with propanediol (PROH) (63/134, 47%). When the zonae were exposed to spermatozoa from fertile donors, those frozen with DMSO showed a significantly higher number of bound spermatozoa than did those frozen with PROH (P < 0.002). In both groups, oocytes which failed to survive the freeze-thaw processes had greater numbers of bound spermatozoa than did those which survived (P < 0.05). Oocytes from cases of failed fertilization showed no difference in their rate of sperm binding compared with oocytes from cases in which some fertilization had occurred. Zonae frozen in PROH but which were from oocytes which were not viable after thawing were used to assess the binding of spermatozoa from men who had failed previously to fertilize their partner's oocytes in vitro and spermatozoa from men with poor quality semen and who had elected for treatment by micro-injection sperm transfer. The number of spermatozoa bound to zonae was reduced significantly in both groups compared to a fertile donor.