Closed versus open vitrification for human blastocyst cryopreservation: A meta-analysis

Closed vitrification can minimize the risk of microbiological transmission through liquid nitrogen during the cooling, storage, and warming procedures. As cooling rates may reduce when closed vitrification is applied, clinical outcomes should be compared between closed and open vitrification in order to justify the use of closed vitrification. This study was conducted to investigate the differences in survival, implantation, clinical pregnancy, and live birth rates between closed and open vitrification for human blastocyst cryopreservation. This systematic review and meta-analysis included 7 studies that reported survival, implantation, clinical pregnancy, or live birth rates following closed or open vitrification. There were no statistically significant differences in survival rates (risk ratio [RR]: 1.00, 95% confidence interval [CI]: 0.98-1.02), implantation rates (RR: 1.02, 95% CI: 0.93-1.11), clinical pregnancy rates (RR: 0.99, 95% CI: 0.89-1.10), and live birth rates (RR: 0.77, 95% CI: 0.58-1.03) between closed and open vitrification. Although there was no statistical significance, the tendency of lower live birth rates with closed vitrification than with open vitrification could be clearly identified. Therefore, it is not yet possible to conclude that closed vitrification clearly provides an aseptic alternative to open vitrification in human blastocyst cryopreservation.