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

Objective: To compare the developmental potential of cryopreserved hum an zygotes after thawing to sibling zygotes that were transferred with out cryopreservation. Methods: Retrospective analysis of embryo data a nd pregnancy outcome for all in vitro fertilization (IVF) patients who had sufficient zygotes to allow fresh embryo transfer and cryopreserv ation of additional sibling zygotes for later use. Results: Zygotes su rvived cryopreservation at a high rate (87%). After thawing, cryoprese rved zygotes developed at rates similar to those of fresh zygotes. Pre gnancy occurred at similar rates after replacement of fresh embryos (2 7.9%) or replacement of cryopreserved-thawed zygote-derived embryos (2 4.3%). Conclusions: Human embryos can be cryopreserved at the pronucle ar zygote stage with little loss of developmental potential. Cryoprese rvation allowed a reduction in the number of embryos transferred durin g an IVF retrieval cycle, thereby reducing the occurrence of multiple pregnancy. The total cumulative pregnancy rate per retrieval cycle dou bled when pregnancies from cryopreserved-thawed zygotes were added to those originating from fresh zygotes.