Post Thawing Survival Rate Of Human Embryos In Slow Freezing Versus Vitrification: A Narrative Review

The study compared the outcomes of slow-freeze and vitrification methods for oocyte cryopreservation, analyzing five randomized controlled trials, two cohort studies, and eight systematic reviews and meta-analyses.Slow-freezeis performed at room temperature using a buffered medium supplemented with gentamicin and human serum albumin. It contains 1.5 M 1,2-propanediol and 0.1 M sucrose. On the other hand, vitrification has been the preferred method since 2007. During vitrification, embryos are initially incubated in a solution consisting of 7.5% ethylene glycol and 7.5% dimethyl sulfide, both in Ham's F-10 media. This solution is further supplemented with 20% Albuminal-5. After the initial recovery, the oocytes are aspirated and immersed in a vitrification solution composed of Ham's F-10 medium for a duration of 50 to 60 seconds. The cooling is done via liquid nitrogen, and embryos are stored for months. The survival rate of embryos is the percentage of those that survive after being warmed up. Live birth rates are calculated as the percentage of live births per transferred embryo and warmed embryo. Embryos are selected by biopsy at the zygote or blastocyst stage using non-invasive methods to optimize the success rates of in vitro fertilization. Vitrification has a greater success rate, better survival rates, and transferable embryos, it is chosen for oocyte cryopreservation. Better clinical pregnancy rates and implantation capacity have also been linked to it, notably for blastocysts from In Vitro Maturation programs. To assess effects on neonatal outcomes and congenital abnormalities, additional study is necessary.