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

Abstract

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 chi2 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.