IN-VITRO DEVELOPMENT AND IMPLANTATION RATES OF FRESH AND CRYOPRESERVED SIBLING ZYGOTES

Objective: To compare the developmental potential of cryopreserved human zygotes after thawing to sibling zygotes that were transferred without cryopreservation. Methods: Retrospective analysis of embryo data and pregnancy outcome for all in vitro fertilization (IVF) patients who had sufficient zygotes to allow fresh embryo transfer and cryopreservation of additional sibling zygotes for later use. Results: Zygotes survived cryopreservation at a high rate (87%). After thawing, cryopreserved zygotes developed at rates similar to those of fresh zygotes. Pregnancy occurred at similar rates after replacement of fresh embryos (27.9%) or replacement of cryopreserved-thawed zygote-derived embryos (24.3%). Conclusions: Human embryos can be cryopreserved at the pronuclear zygote stage with little loss of developmental potential. Cryopreservation allowed a reduction in the number of embryos transferred during an IVF retrieval cycle, thereby reducing the occurrence of multiple pregnancy. The total cumulative pregnancy rate per retrieval cycle doubled when pregnancies from cryopreserved-thawed zygotes were added to those originating from fresh zygotes.