FERTILIZATION OF HUMAN OOCYTES FOLLOWING CRYOPRESERVATION - NORMAL KARYOTYPES AND ABSENCE OF STRAY CHROMOSOMES

Survival folllowing cryopreservation of fresh and aged human oocytes b y the propanediol (PROH) procedure was observed in 51 and 73% of oocyt es respectively, immediately after thawing. This survival was reduced in both types of oocytes at the time of insemination (3-4 h) to 41% in fresh and 61% in aged oocytes. Insemination of the cryopreserved and control oocytes with spermatozoa from one donor resulted in total fert ilization rates similar to our in-vitro fertilization (IVF) rate for n on-male factor patients. The normal fertilization rate for fresh cryop reserved oocytes was slightly lower (46%) than the rate for IVF oocyte s (59%) (P < 0.05), while the abnormal fertilization rates were not si gnificantly different (16 and 15% respectively). In contrast, a reduct ion in the normal fertilization rate was observed for the aged cryopre served oocytes (13%) compared to the IVF rate (P < 0.001). Associated with this was an increase in the abnormal fertilization rate for the a ged cryopreserved oocytes, which was significantly higher (47%) than t he IVF rate (15%) (P < 0.001). Significant differences in the total an d normal fertilization rates were observed between cryopreserve oocyte s obtained from cohorts with less than or equal to 27 (total: 84%, nor mal: 68%) and > 27 oocytes (total: 55%, normal: 33%) (P < 0.05). Ferti lized oocytes and oocytes with abnormal or absent spindles were examin ed for chromosomal loss and no stray chromosomes were observed in any of these cryopreserved oocytes (n = 137). In the cryopreserved oocytes which had undergone normal fertilization, four scorable karyotypes we re achieved and in all of these two sets of 23 chromosomes were observ ed.