Oocyte, embryo and blastocyst cryopreservation in ART: systematic review and meta-analysis comparing slow-freezing versus vitrification to produce evidence for the development of global guidance

Abstract

BACKGROUNDSuccessful cryopreservation of oocytes and embryos is essential not only to maximize the safety and efficacy of ovarian stimulation cycles in an IVF treatment, but also to enable fertility preservation. Two cryopreservation methods are routinely used: slow-freezing or vitrification. Slow-freezing allows for freezing to occur at a sufficiently slow rate to permit adequate cellular dehydration while minimizing intracellular ice formation. Vitrification allows the solidification of the cell(s) and of the extracellular milieu into a glass-like state without the formation of ice.OBJECTIVE AND RATIONALEThe objective of our study was to provide a systematic review and meta-analysis of clinical outcomes following slow-freezing/thawing versus vitrification/warming of oocytes and embryos and to inform the development of World Health Organization guidance on the most effective cryopreservation method.SEARCH METHODSA Medline search was performed from 1966 to 1 August 2016 using the following search terms: (Oocyte(s) [tiab] OR (Pronuclear[tiab] OR Embryo[tiab] OR Blastocyst[tiab]) AND (vitrification[tiab] OR freezing[tiab] OR freeze[tiab]) AND (pregnancy[tiab] OR birth[tiab] OR clinical[tiab]). Queries were limited to those involving humans. RCTs and cohort studies that were published in full-length were considered eligible. Each reference was reviewed for relevance and only primary evidence and relevant articles from the bibliographies of included articles were considered. References were included if they reported cryosurvival rate, clinical pregnancy rate (CPR), live-birth rate (LBR) or delivery rate for slow-frozen or vitrified human oocytes or embryos. A meta-analysis was performed using a random effects model to calculate relative risk ratios (RR) and 95% CI.OUTCOMESOne RCT study comparing slow-freezing versus vitrification of oocytes was included. Vitrification was associated with increased ongoing CPR per cycle (RR = 2.81, 95% CI: 1.05–7.51; P = 0.039; 48 and 30 cycles, respectively, per transfer (RR = 1.81, 95% CI 0.71–4.67; P = 0.214; 47 and 19 transfers) and per warmed/thawed oocyte (RR = 1.14, 95% CI: 1.02–1.28; P = 0.018; 260 and 238 oocytes). One RCT comparing vitrification versus fresh oocytes was analysed. In vitrification and fresh cycles, respectively, no evidence for a difference in ongoing CPR per randomized woman (RR = 1.03, 95% CI: 0.87–1.21; P = 0.744, 300 women in each group), per cycle (RR = 1.01, 95% CI: 0.86–1.18; P = 0.934; 267 versus 259 cycles) and per oocyte utilized (RR = 1.02, 95% CI: 0.82–1.26; P = 0.873; 3286 versus 3185 oocytes) was reported. Findings were consistent with relevant cohort studies.Of the seven RCTs on embryo cryopreservation identified, three met the inclusion criteria (638 warming/thawing cycles at cleavage and blastocyst stage), none of which involved pronuclear-stage embryos. A higher CPR per cycle was noted with embryo vitrification compared with slow-freezing, though this was of borderline statistical significance (RR = 1.89, 95% CI: 1.00–3.59; P = 0.051...

Fresh and Frozen-Thawed Embryo Transfer Compared to Natural Conception: Differences in Perinatal Outcome

“…A recent review showed a slightly favorable cryosurvival and clinical pregnancy rate for vitrification instead of slow-freezing as cryopreservation technique for embryos [37]. We solely use slow-freezing in our center, so this has no implication on our findings.…”

Recidiva de teratoma ovárico tras encefalitis anti-NMDA y manejo de la fertilidad: caso clínico.

“…Sin embargo, es variable el impacto que esta puede ejercer sobre la fertilidad(16)(17), probablemente muy en relación con la naturaleza del quiste, tipo de cirugía realizada y la experiencia del cirujano(18), además de la edad de la mujer y la edad que tenga en el momento de búsqueda de gestación. No obstante, el efecto que una nueva cirugía puede tener sobre la fertilidad y la alta eficacia de los programas de vitrificación ovocitaria en la actualidad (19) (20), lleva a contemplar la opción de la criopreservación de ovocitos ante cirugías ováricas repetidas.…”

International Multicenter Egg Donation Program (IMEDO): preliminary outcomes

“…Two cryopreservation methods are routinely used: slow-freezing or vitrification. In our work the method chosen was vitrification that has now become the method of choice for oocyte cryopreservation (4,5). The high request of heterologous fertilization (especially egg donation) and the improvements in cryopreservation techniques, stimulated centers of assisted reproduction in creating strategies for the collection, cryopreservation, transport abroad and use of gametes.…”