A closed system supports the developmental competence of human embryos after vitrification : Closed vitrification of human embryos.

Abstract

Closed-system vitrification may enable the risk of contamination to be minimised. We performed three studies to compare the developmental competence of human embryos vitrified using either a closed vitrification system (CVS; Rapid-i®) or an open vitrification system (OVS; Cryo-top®). The first study was performed in vitro using 66 zygotes previously vitrified at pronuclear stage. These were warmed and randomised 1:1 to revitrification using either the OVS or the CVS. After re-warming, embryo development and blastocyst cell number were assessed. For the second study, also performed in vitro, 60 vitrified-warmed blastocysts were randomised 1:1:1 into three groups (OVS or CVS revitrification, or no revitrification). The proportion of dead cells was assessed by staining. The third study was performed in vivo, using 263 high-grade blastocysts randomly assigned to vitrification using either the CVS (n = 100) or the OVS (n = 163). After warming, single blastocyst transfer was performed. There were no differences between the CVS and the OVS in survival rate (100% vs. 97%), blastulation rate (96h: 50% vs. 50%; 120h: 68% vs. 56%), proportion of good blastocysts (96h: 32% vs. 22%, 120h: 47% vs. 41%), or mean number of cells (137 vs. 138). The proportion of dead cells in blastocysts re-vitrified by CVS (31%) was similar to that for OVS (38%) and non-revitrification (32%). In vivo, the implantation rate for blastocysts vitrified using the CVS (54%) was similar to that with the OVS (53%). Our studies consistently indicate that human embryos may be vitrified using a CVS without impairment of developmental competence.