A pragmatic RCT of conventional versus increased concentration sucrose in freezing and thawing solutions for human embryos

Appendix F: Quinn's Advantage Embryo Freeze Kit

Despite a large focus on the use of vitrification to cryopreserve embryos in recent years, there are still arguments for the use of slow freezing for the cleavage-stage embryo. Having said this, there are lessons to be learned from the process of vitrification that could be applied to slow freezing to improve post-thaw survival and ultimately clinical pregnancy rates. Specifically, increasing the concentration of sucrose in the freezing solution from 0.1 to 0.2 M and subsequently increasing the sucrose concentrations in thawing solutions could prove beneficial. The use of vitrification warming solutions in the thawing of slow-frozen embryos may also be an option that not only improves survival but also streamlines product purchasing and protocols within the laboratory.

Human embryo cryopreservation: one-step slow freezing does it all?

PURPOSE

Previous studies have shown that a modified one-step slow freezing method with higher sucrose concentration (0.2 M) can achieve higher embryo and blastomere survival rates that are comparable to vitrification. However, no study has evaluated the efficacy of a one-step method using commercial slow freezing kit without altering its composition. This retrospective study examines the effects of using 1.5 M PROH with 0.1 M sucrose (F2 medium) alone in a one-step slow freezing method compared to the conventional two-step method.

METHODS

Cleavage stage embryos from 526 thaw cycles previously cryopreserved by either the conventional two-step slow freezing method or the modified one-step method were studied. The embryo and blastomere survival rates, cleavage rate, clinical pregnancy rate and live birth rate were compared between the two groups.

RESULTS

The results showed that the embryo survival rate was significantly higher in the modified one-step method compared to the conventional two-step method (86.9 % and 83.1 %, respectively; p = 0.04). Total blastomere survival rate was also significantly increased as a result of the modification (81.0 % versus 76.5 %; p < 0.001). However, there was no statistical difference in the cleavage rates, clinical pregnancy rates (CPR/ET) and live birth rates between the two methods.

CONCLUSIONS

Slow freezing using the one-step method is superior to the conventional two-step method in terms of embryo and blastomere survival rates without affecting cleavage rate and clinical outcomes. It can be routinely applied to cleavage stage embryo cryopreservation in IVF centres for greater workflow efficiency.

A randomized controlled trial comparing two vitrification methods versus slow-freezing for cryopreservation of human cleavage stage embryos

Purpose

To compare two different vitrification methods to slow freezing method for cryopreservation of human cleavage stage embryos. Design: Prospective randomised trial. Setting: University assisted reproduction centre. Patient(s): 568 patients (mean age 33.4 ± 5.2) from April 2009 to April 2011.

Methods

1798 supernumerary good-quality cleavage stage embryos in 645 IVF cycles intended to be cryopreserved were randomly allocated to three groups: slow freezing, vitrification with the Irvine® method, vitrification with the Vitrolife® method. Main Outcome Measure(s): Embryo survival and cleavage rates, implantation rate.

Results

A total of 1055 embryos were warmed, 836 (79.2 %) survived and 676 were finally transferred (64.1 %). Post-warming embryos survival rate was significantly higher after vitrification (Irvine: 89.4 %; Vitrolife: 87.6 %) than after slow freezing (63.8 %) (p < 0.001). No differences in survival rates were observed between the two vitrification methods, but a significant higher cleavage rate was observed using Irvine compared to Vitrolife method (p < 0.05). Implantation rate (IR) per embryo replaced and per embryo warmed were respectively 15.8 % (41/259) and 12.4 % (41/330) for Irvine, 17.0 % (40/235) and 12.1 % (40/330) for Vitrolife, 21.4 % (39/182) and 9.9 % (39/395) for slow-freezing (NS).

Conclusions

Both vitrification methods (Irvine and Vitrolife) are more efficient than slow freezing for cryopreservation of human cleavage stage embryos in terms of post-warming survival rate. No significant difference in the implantation rate was observed between the three cryopreservation methods.

Viability of human ovarian tissue confirmed 5 years after freezing with spontaneous ice-formation by autografting and chorio-allantoic membrane culture

To achieve optimal and uniform outcomes, slow cooling protocols for human ovarian tissues generally initiate ice formation at high sub-zero temperatures (-6 to -9 °C). The aim of the study was to investigate the function of ovarian tissue that had unintentionally self seeded at -20 °C during the freezing step, by examining its development following chicken embryonic chorioallantoic membrane (CAM) grafting and after transplantation back to the patient. Ovarian tissue was frozen in 6% (v/v) dimethyl sulfoxide, 6% (v/v) ethylene glycol and 0.15M sucrose which had self-seeded at -20 °C. Five years after cryopreservation, 8 pieces were thawed and transplanted back to the patient. Two small (1 × 2 × 1 mm) pieces of this thawed tissue were cultured in a CAM-system for 5 days to assess the tissue viability. The autografted ovarian tissue re-established spontaneous menstrual bleeding within five months and raised serum 17-β Estradiol from 19 to 330 pg/ml. Ultrasound revealed a dominant follicle at the site of the transplanted tissue in the follicular phase after the menstrual bleed. Analysis of the CAM cultured tissue established that 88% of the primordial follicles are degenerated and there was limited in growth of blood vessels. In conclusion, in spite of the damage caused by the cryopreservation with spontaneous ice-formation the viability could be confirmed by CAM culture and the restoration of ovarian function after auto-transplantation.

ACE consensus meeting report: oocyte and embryo cryopreservation Sheffield 17.05.11

The UK Association of Clinical Embryologists (ACE) held a consensus workshop on Oocyte and Embryo Cryopreservation in Sheffield, UK, on May 17th, 2011. This was organized in response to a number of considerations including the increasing prevalence of vitrification for oocyte and embryo cryopreservation in the UK and worldwide, coupled with an apparent lack of consensus over which methods of cryopreservation are optimal. The workshop included expert opinion and survey data on current practice provided by participating clinics. The workshop highlighted that an increasing number of clinics in the UK are choosing vitrification rather than controlled rate freezing, particularly for the storage of oocytes and blastocysts. It was evident that a variety of solutions are used in conjunction with open and closed containers. Data supplied by the participating clinics suggest that both freezing and vitrification can lead to similar outcomes in early embryos and blastocysts and at the moment there is no evidence base to recommend either method over the other. The delegates arrived at a number of consensus points which reflected current practice in the UK, but recognized the need for well-designed trials with careful follow up of the children born before optimal methods can be agreed.

A critical appraisal of cryopreservation (slow cooling versus vitrification) of human oocytes and embryos

BACKGROUND

Vitrification is now a commonly applied technique for cryopreservation in assisted reproductive technology (ART) replacing, in many cases, conventional slow cooling methodology. This review examines evidence relevant to comparison of the two approaches applied to human oocytes and embryos at different developmental stages.

METHODS

Critical review of the published literature using PubMed with particular emphasis on studies which include data on survival and implantation rates, data from fresh control groups and evaluation of the two approaches in a single setting.

RESULTS

Slow cooling is associated with lower survival rates and compromised development relative to vitrification when applied to metaphase II (MII) oocytes, although the vitrification results have predominantly been obtained using direct contact with liquid nitrogen and there is some evidence that optimal protocols for slow cooling of MII oocytes are yet to be established. There are no prospective randomized controlled trials (RCTs) which support the use of either technique with pronuclear oocytes although vitrification has become the method of choice. Optimal slow cooling, using modifications of traditional methodology, and vitrification can result in high survival rates of early embryos, which implant at the same rate as equivalent fresh counterparts. Many studies report high survival and implantation rates following vitrification of blastocysts. Although slow cooling of blastocysts has been reported to be inferior in some studies, others comparing the two approaches in the same clinical setting have demonstrated comparable results. The variation in the extent of embryo selection applied in studies can lead to apparent differences in clinical efficiency, which may not be significant if expressed on a 'per oocyte used' basis.

CONCLUSIONS

Available evidence suggests that vitrification is the current method of choice when cryopreserving MII oocytes. Early cleavage stage embryos can be cryopreserved with equal success using slow cooling and vitrification. Successful blastocyst cryopreservation may be more consistently achieved with vitrification but optimal slow cooling can produce similar results. There are key limitations associated with the available evidence base, including a paucity of RCTs, limited reporting of live birth outcomes and limited reporting of detail which would allow assessment of the impact of differences in female age. While vitrification has a clear role in ART, we support continued research to establish optimal slow cooling methods which may assist in alleviating concerns over safety issues, such as storage, transport and the use of very high cryoprotectant concentrations.