Clinical application of oocyte vitrification: a systematic review and meta-analysis of randomized controlled trials.

OBJECTIVE: To perform a systematic review of the literature to identify randomized controlled trials assessing the efficacy of oocyte vitrification in terms of oocyte survival, fertilization, embryo development, and pregnancy rates.
DESIGN: Systematic review and meta-analysis of randomized controlled trials.
SETTING: Private university-affiliated IVF center, university-based hospital. PATIENT(S): Patients recruited in randomized controlled trials considering oocyte vitrification as one of the experimental arms and slow freezing or fresh oocytes control as the other. INTERVENTION(S): Vitrification of human oocytes vs. slow freezing or fresh oocytes. MAIN OUTCOME MEASURE(S): Ongoing pregnancy rate; secondary outcomes were clinical pregnancy rate, implantation rate, embryo development, fertilization rate, and oocyte survival. RESULT(S): Five eligible studies were finally included. They involved 4,282 vitrified oocytes, 3,524 fresh oocytes, and 361 slow-frozen oocytes between 2005 and 2009. The rates of ongoing pregnancy, top-quality embryo, embryo cleavage, and fertilization did not differ between the vitrification and the fresh oocyte groups. The oocyte survival rate was higher in vitrified vs. slow-frozen oocytes (odds ratio [OR] 2.46, 95% confidence interval [CI] 1.82-3.32), although heterogeneity between studies was observed. The fertilization rate was higher in vitrified vs. slow-frozen oocytes (OR 1.50, 95% CI 1.07-2.11). Vitrification also resulted in a higher rate top-quality embryo (22.4% vs. 8.0%, OR 3.32, 95% CI 1.37-8.02) and embryo cleavage rate (day 2: 64.6% vs. 47.7%, OR 2.00, 95% CI 1.33-3.00; day 3: 53.0% vs. 33.3%, OR 2.25, 95% CI 1.32-3.85) as compared with slow freezing. CONCLUSION(S): Vitrification is an efficient method to preserve oocytes, although more large controlled clinical trials are needed to strengthen this conclusion.