VITRIFICATION, NEW METHOD OF EMBRYO CRYOPRESERVATION: MARIBOR EXPERIENCE

Background. Vitrification is a new, simpler and more rational way of cryopreservation of redundant embryos in in vitro fertilisation. The purpose of this study was to introduce vitrification of blastocysts in clinical practice and compared two commercial cryoprotectants. Methods. We started vitrifying blastocysts in 2008. Two commercial vitrification protocols were used, Vitrification Cooling/Warming (MediCult, Denmark) – (MC), and Vitrification Freeze/Thaw (IrvineScientific, ZDA) – (IS). IS medium includes two cryoprotectants: dimethylsulfoxide (DMSO) and ethylene glycol, meanwhile MC medium contains only ethylene glycol. Among 1030 in vitro fertilizated cycles, we preserved redundant blastocysts in 404 (39.2 %) cycles in liquid nitrogen. At the begining MC vitrification protocol was used in 253 cycles and later IS protocol in 151 cycles. 127 transfers (248 devitrified blastocysts) were performed using MC protocol and 71 transfers (124 blastocysts) using IS protocol. We compared the survival rate of blastocysts, rate of clinical and ongoing pregnancies and miscarriages. Cycles with at least one optimal blastocyst were evaluated separately. Results. Survival rate of vitrified blastocysts by IS protocol was statistically significantly higher than survival rate by MC protocol (88.7 % or 77 %; P = 0.0103). Implantation rate of devitrified blastocysts by IS and MC protocol are comparable (22.7 % or 17.8 %). The rate of miscarriages does not statistically differ between the protocols (18.2 % or 16.7 %). There are no statistically significant differences between IS and MC protocols in clinical (31.8 % or 24 %) and ongoing pregnancies (26.1 % or 20 %). Pregnancy rate in cycles with at least one optimal devitrified blastocyst is 45.7 % by IS protocol and 36.4 % by MC protocol. In the same cycles, the rate of miscarriages is 5.7 % by IS and 4.5 % by MC protocol. Conclusions. Higher values in all parameters were by IS media, even though the differences were not statistically significant because of low number of cycles. The only statistically significant difference between protocols was in survival rate in favor of IS protocol. The study continues