A flexible protocol for cryopreservation of pronuclear and cleavage stage embryos created by conventional in vitro fertilization and intracytoplasmic sperm injection

Objectives: To evaluate the hospital's cryopreservation protocol. Study design: A retrospective cohort analysis of 30 conventional IVF and 44 ICSI cycles in an assisted conception unit at a tertiary referral hospital. All supernumerary embryos were cryopreserved at the pronuclear or blastomere stage. The survival, morphology, implantation and pregnancy rates were evaluated. The chi(2) 2 test and Fisher's exact test were used to determine the statistical significance. Results: A total of 327 pronuclear and cleavage stage embryos were cryopreserved. The post thaw survival rates of 107 conventional IVF and 220 ICSI embryos were 90.6% and 69.0%, respectively. Of the thawed cleavage stage embryos from 43 IVF and 88 ICSI cycles, 90.6% and 69.3% were intact, respectively. Of the thawed pronuclear stage embryos from 64 IVF and 132 ICSI cycles, 90.6% and 68.9% were intact with cleavage rates of 57.8% and 56%, respectively. In the final 27 conventional IVF and 41 ICSI frozen-thawed embryo transfer cycles, the pregnancy rates were 18.5% and 19.5%, respectively. Conclusions: The adopted cryopreservation protocol flexibly allows for the selection of cleavage-stage embryos for fresh embryo transfer and the cryopreservation of all supernumerary embryos at the pronuclear or the cleavage stage in a single cycle with satisfactory pregnancy rates. Further validation of this protocol is required. (C) 2004 Elsevier Ireland Ltd. All rights reserved.