Abstract
BackgroundThe objective of this study was to carry out a systematic review and meta-analysis of embryologic and clinical outcomes following open versus closed vitrification of human oocytes and embryos.MethodsAn electronic literature search was conducted in main electronic databases up to June 30, 2018 using the following key terms: ‘oocyte’, ‘embryo’, ‘blastocyst’, ‘vitrification’, ‘cryopreservation’, ‘device’, ‘survival rate’, ‘pregnancy rate’, etc. A meta-analysis was performed using a random effect model to estimate the value of risk ratios (RRs) and 95% confidence interval (CI). Subgroup analyses and sensitivity analyses were carried out to further confirm the results.ResultsTwelve (Eight prospective and four retrospective) studies comparing open versus closed vitrification of human oocytes or embryos were included. For prospective studies on oocytes, no evidence for a significant difference in cryosurvival rate (RR = 0.91, 95% CI: 0.80–1.03, P = 0.14; n = 2048) or clinical pregnancy rate (RR = 1.29, 95% CI: 0.80–2.06, P = 0.30; n = 150) was observed. Additionally, there were no significant differences between the two methods concerning secondary endpoints included positive βHCG rate, implantation rate, miscarriage rate, ongoing pregnancy rate, live birth rate, cancellation rate, babies born per transferred blastocysts, or multiple birth rate (P > 0.05). The results of the retrospective studies were similar as the prospective studies.ConclusionsIt is still impossible to conclude that closed vitrification system could be a substitution for open system in human oocyte and embryo cryopreservation based on current evidence. Therefore, more well-designed prospective studies addressing these issues are still warranted.
Highlights
The objective of this study was to carry out a systematic review and meta-analysis of embryologic and clinical outcomes following open versus closed vitrification of human oocytes and embryos
Identification of literature All studies comparing open versus closed vitrification of oocytes and/or embryos on embryologic and clinical reproductive outcomes were considered eligible in this systematic review and meta-analysis
BB babies born per transferred blastocysts, CaR cancellation rate, CBS Cryo Bio System, ClR cleavage rate, CPR clinical pregnancy rate, CsR cryosurvival rate, FR fertilization rate, GQER good quality embryo rate, HSV high security straws, IR implantation rate, LBR: live birth rate, MBR multiple birth rate, MR miscarriage rate, NM not mentioned, OPR ongoing pregnancy rate, PβR positive βHCG rate
Summary
The objective of this study was to carry out a systematic review and meta-analysis of embryologic and clinical outcomes following open versus closed vitrification of human oocytes and embryos. With its high efficiency and consistency, vitrification is becoming the principal approach for cryopreservation of human oocytes and embryos, taking the place of traditional slow freezing in ART [1]. While open vitrification reaches extreme high cooling rates due to direct contact with LN2, risks for potential cross-contamination and disease transmission mediated through LN2 increase when considering long-term cryopreservation. Closed vitrification can avoid direct contact with LN2 by substituting the high concentration of cryoprotectant, influencing the efficiency of cooling [1]. Concerns about the long-term effects of vitrification on large-scale oocytes and embryos when using high concentrations of cryoprotectant, which is regarded as cytotoxic, still exist. It is still argued that the exposure of samples in open containers where environmental pathogens may exist can raise the contingent infectious danger for any IVF laboratory [12]
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