A randomized controlled study of human Day 3 embryo cryopreservation by slow freezing or vitrification: vitrification is associated with higher survival, metabolism and blastocyst formation

Abstract

BACKGROUND: The aim of this study was to compare two methods of cryopreservation for the cleavage-stage human embryo: slow freezing and vitrification. METHODS: A total of 466 Day 3 embryos, donated with consent, underwent cryopreservation by either slow freezing in straws or vitrification using the cryoloop. The vitrification procedure did not include dimethyl sulfoxide, but rather employed ethylene glycol and 1,2-propanediol as the cryoprotectants. Survival, embryonic metabolism and subsequent development to the blastocyst were used to determine the efficacy of the two procedures. RESULTS: Significantly, more embryos survived the vitrification procedure (222/234, 94.8%) than slow freezing (..