NEWS: A novel closed vitrification device reported to be effective to vitrify cleavage and blastocyst stage embryos

Open vitrification devices for embryo cryopreservation allow direct contact between embryo samples and liquid nitrogen, posing a risk of infection or cross-contamination between specimens. The advent of closed vitrification devices has circumvented these risks associated with open vitrification devices. A recent study highlights that Rapid-iTM, a new closed vitrification device, serves as an excellent alternative to the current open vitrification devices to cryopreserve embryos at the cleavage as well as the blastocyst stage.

Nina N Desai and coworkers from the Department of Ob/Gyn/Women’s Health Institute, Cleveland Clinic Fertility Center, Beachwood, USA, compared the efficacy of Rapid-i with that of cryoloop, an open vitrification device, to cryopreserve early and late-stage embryos. A two-step vitrification protocol was followed. Embryos were rinsed and held for 2 minutes (3 minutes for blastocysts) in vitrification solution #1 which contained 7.5% dimethylsulfoxide (DMSO) and 7.5% ethylene glycol (EG) in Global medium with 20% synthetic protein supplement (SPS). Subsequently, they were quickly moved through three drops of vitrification solution #2 (15% DMSO, 15% EG, 10 mg/mL Ficoll-70 and 0.65 M sucrose), being held for 15 seconds in each drop and then loaded on the vitrification carrier. Cryoprotective agents were removed during warming by two successive washes in 0.25 M and 0.125 M sucrose in culture medium. Main outcomes evaluated were embryo survival (>50% intact), morphology at transfer, implantation rate, and clinical pregnancy rate per transfer. Clinical outcomes of frozen embryo transfer between January 2011 and August 2012 were stratified based on the carrier for vitrification and cell stage.

Totally, 468 vitrified-warm embryos were evaluated, out of which 92% were transferred. The study, published in the journal Reproductive Biology and Endocrinology, revealed the following findings (Table 1):

  • implantation and clinical pregnancy rates obtained with cleavage stage embryos vitrified using Rapid-i were comparable to those vitrified using cryoloop
  • implantation and clinical pregnancy rates achieved with blastocyst stage embryos vitrified using Rapid-i were slightly higher than those obtained with cryoloop, the differences, however, did not reach statistical significance

Table 1: Vitrification outcomes for cleavage and blastocyst stage embryos using Rapid-i and cryoloop

Rapid-i, a novel closed vitrification device, has recently been approved by the FDA for embryo vitrification. It is based on the same principle as the cryoloop. Embryos are placed in a miniscule drop of vitrification solution within a hole on a cylindrical stick, which can be totally enclosed and sealed to prevent direct contact with liquid nitrogen. The design of Rapid-i, which resembles cryoloop, facilitates easy loading and unloading of embryos, when compared to other closed vitrification devices. The cooling rate of Rapid-i (-12200C/min) is 15-fold lesser than that reported with cryoloop (−15,0000C/min).

Achieving high cooling rates has been the basic principle underlying the design of new vitrification devices. Consequently, concerns have been raised about the reduced cooling rate of closed vitrification devices when compared to the open systems, resulting in ice crystal formation inside and outside cells leading to cell death and reduced developmental capacity. However, previous trials have indicated that cryoinjury may be associated with recrystallization during warming rather than vitrification failure. Warming rate, rather than the cooling rate, has been suggested to play a crucial role in regulating survival rates, post vitrification. A minimum warming rate of 30000C/min has been speculated to be necessary to achieve a survival rate of 80%, and if the warming is quick enough, a low cooling rate (−2000C/min) has been suggested to be sufficient for successful vitrification.

The current study demonstrates that despite the far low warming (77000C/min) and cooling (−12200C/min) rates of Rapid-i compared to other vitrification devices, the clinical outcomes achieved are comparable to those obtained using the cryoloop. These encouraging findings may herald the transition from open to closed vitrification system in IVF units. However, additional data are required to substantiate these preliminary study findings.

References

  • Desai NN, Goldberg JM, Austin C, Falcone T. The new Rapid-i carrier is an effective system for human embryo vitrification at both the blastocyst and cleavage stage. Reprod Biol Endocrinol. 2013 May 15;11(1):41.
  • AbdelHafez F, Xu J, Goldberg J, Desai N. Vitrification in open and closed carriers at different cell stages: assessment of embryo survival, development, DNA integrity and stability during vapor phase storage for transport. BMC Biotechnol. 2011 Mar 30;11:29.
  • Enrique Criado Scholz (2012). The Problem of Contamination: Open vs. Closed vs. Semi-Closed Vitrification Systems, Current Frontiers in Cryopreservation, Prof. Igor Katkov (Ed.), ISBN: 978-953-51-0302-8, InTech, Available from: http://cdn.intechopen.com/pdfs/31862/InTech-The_problem_of_contamination_open_vs_closed_vs_semi_closed_vitrification_systems.pdf

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