An evaluation of embryo, zygote and oocyte cryopreservation in assisted reproductive technology

The study compared (i) the outcome between cryopreserved ICSI fertilized embryo and cryopreserved ICSI fertilized pronuclear stage zygotes and (ii) the outcome between cryopreserved fertilized mature oocytes with cryopreserved immature oocytes, fertilized by ICSI following thawing. Comparative retrospective review of relevant studies satisfying study criteria. Studies were identified through MEDLINE literature search. Study outcomes were cryosurvival, fertilization, implantation, pregnancy, and delivery rates. Pronucleate zygotes had better cryosurvival rates than the cleaving embryo (90.7% versus 59.9%) and almost double the clinical pregnancy rates for cleaving embryo (12.8% versus 7.0%). There was an almost three-fold higher delivery rate for the pronucleate zygote compared with cleaving embryo (11.6% versus 4.3%). Immature oocytes had lower cryosurvival rates than mature oocytes (34.5% versus 52.3%). Mature and immature oocytes showed good fertilization rates (59.3% versus 50%) and satisfactory embryonic development (90.3% versus 100.0%). Immature oocytes had higher delivery rate per embryo transferred than the mature oocyte (40.0% versus 2.7%). Pronucleate zygote cryopreservation has an advantage over the cleaving embryo. The low survival rate following thawing is still an obstacle to the integration of oocyte cryopreservation into ART.