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.