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

Abstract

Purpose 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®). Methods 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. Results There were no differences between the CVS and the OVS in survival rate (100 % vs. 97 %), blastulation rate (96 h: 50 % vs. 50 %; 120 h: 68 % vs. 56 %), proportion of good blastocysts (96 h: 32 % vs. 22 %, 120 h: 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 %).Conclusion Our studies consistently indicate that human embryos may be vitrified using a CVS without impairment of developmental competence.

Neonatal outcomes after the implantation of human embryos vitrified using a closed-system device

“…Such cross-contamination could arise from direct contact of the solution containing the oocytes and embryos with the liquid nitrogen. Therefore, to avoid the possible risk of contamination, closed vitrification systems have been developed [15][16][17][18][19][20][21][22][23][24][25]. However, new concerns such as a potential rise in temperature caused by a heat sealer and a decrease in the cooling rate have emerged with these methods.…”

“…We recently reported no significant difference between the use of closed and open vitrification systems in the survival rate, blastulation rate, proportion of good blastocysts, mean number of cells, or implantation rate [24]. In this closed system, an embryo is inserted into a straw with super-cooled air for vitrification, and its open end is sealed using ultrasound adhesion to avoid the risks of increased temperature and contamination.…”

Survival, re-expansion and cell survival of human blastocysts following vitrification and warming using two vitrification systems

“…Cell damage, assessed in terms of DNA damage, was found to be similar between embryos vitrified with open and closed carriers [17]. Similarly, a recent report showed no difference in terms of percentage of dead cells, between open and closed vitrification systems, where cooling rates were slower [20].…”

“…The assessment of different vitrification systems is frequently done using animal embryos [14][15][16][17], discarded human embryos [18,19] or embryos donated for research purposes [20]. These studies commonly included evaluation of survival following vitrification/warming, subsequent development and re-expansion [17,20].…”

“…These studies commonly included evaluation of survival following vitrification/warming, subsequent development and re-expansion [17,20]. For protocols involving slower cooling rates, it is important to assess cell damage after vitrification because of the possibility that lower cooling rates may lead to ice crystal formation both inside and outside the blastocyst and thereby cause cell death.…”