Hum. Reprod. Advance Access originally published online on June 10, 2008
Human Reproduction 2008 23(9):1976-1982; doi:10.1093/humrep/den222
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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
1 Assisted Reproduction Unit, American Hospital of Istanbul, Guzelbahce Sokak 20, Nisantasi, Istanbul 34365, Turkey 2 Colorado Center for Reproductive Medicine, Lone Tree, CO, USA
4 Correspondence address. Tel: +90-212-3112000; Fax: +90-212-3112339; E-mail: burman{at}superonline.com
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 (206/232, 88.7%; P < 0.05). Consistent with this observation, pyruvate uptake was significantly greater in the vitrification group, reflecting a higher metabolic rate. Development to the blastocyst was also higher following vitrification (134/222, 60.3%) than following freezing (106/206, 49.5%; P < 0.05). In a separate cohort of 73 patients who had their supernumerary embryos cyropreserved with vitrification, the resulting implantation rate and clinical pregnancy rate were 30 and 49%, respectively.
CONCLUSIONS: Analysis of metabolism revealed that vitrification had less impact on the metabolic rate of the embryo than freezing, which was reflected in higher survival rate and subsequent development in vitro. Excellent pregnancy outcomes followed the warming and transfer of vitrified cleavage-stage embryos. These data provide further evidence that vitrification imparts less trauma to cells and is, therefore, a more effective means of cryopreserving the human embryo than conventional slow freezing. Clinicaltrials.gov identifier: NCT00608010 [ClinicalTrials.gov] .
Key words: cryopreservation/vitrification/propanediol/pyruvate uptake/blastocyst development
Preliminary results of this trial have been presented at the 63rd ASRM meeting, Washington, USA, October 2007 and at the Nordic IVF Laboratory Society Meeting, Helsinki, Finland, November 2007. 3 Present address: Department of Zoology, University of Melbourne, Victoria, Australia
Submitted on February 25, 2008; resubmitted on May 9, 2008; accepted on May 13, 2008.
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