From a Backup Technology to a Strategy-Outlining Approach

The Success Story of Cryopreservation

Gábor Vajta; Anikó Reichart; Filippo Ubaldi; Laura Rienzi

Disclosures

Expert Rev of Obstet Gynecol. 2013;8(2):181-190. 

In This Article

Breaking the Monopoly

For approximately two decades, slow-rate freezing was the only acceptable method in the human embryology laboratory. Although introduced in mammalian embryology in 1986,[10] the existence of vitrification was neglected and early achievements, both in human embryo and oocyte cryopreservation,[11–14] were just regarded as a scientific curiosity. Retrospectively, many factors contributed to this bias, predominantly the conservative mentality in human-assisted reproduction. Although this increasingly defensive behavior – supported or rather enforced by authorities – is partially understandable, eventually it may seriously hamper us in fulfilling our common goal and destiny.

Other factors included the total lack of industrial background.Commercial companies were less than interested in propagating a method that can be performed in a foam box. This approach is changing slowly, but it is not without its controversies. We now have a large choice of media and carrier tools, but the average price is absurd and thus is prohibitive for many IVF units. On the other hand, very few steps were taken to improve work safety (discussed later) and towards automation of the procedure.

There were and still are major concerns regarding the lack of basic scientific background and safety of vitrification. These arguments are seemingly sound, at least for laymen. However, in our profession, which has been established by one of the bravest and, retrospectively, the most praised step in biological sciences, the creation of the first test-tube baby, without having any ideas about the potential consequences; where the alternative and widely used cryopreservation method was introduced earlier with even less basic scientific background, the moral and practical meanings of such statements are quite different (discussed later). For safety purposes, high cryoprotectant concentrations with potential toxicity are always referred, disregarding the fact that the final intracytoplasmic concentration of cryoprotectants is much higher in traditional freezing than in vitrification.[15] Specific toxicity of some components, predominantly dimethyl sulfoxide (DMSO) are often cited. Some companies and researchers even advertise their 'nontoxic', that is, DMSO-free, vitrification systems, although DMSO is probably the least toxic and most protective cryoprotectant compared with other commonly used permeable ones, such as propylene glycol.[16–19] Finally, the theoretical danger of liquid nitrogen-mediated disease transmission is a most regrettable and absurd misinterpretation of scientific evidences, leading to fruitless arguments and the potential ban of the most efficient vitrification techniques (also discussed later).

Fortunately, for some scientists the potential gain outweighed these concerns. Again, fortunately, their results were published at the right moment, when the need for a more efficient technology occurred in relatively new fields: blastocyst and oocyte cryopreservation. Traditional slow-rate freezing was efficient for cleavage, precompaction stage human embryos, but in vitro survival and in vivo developmental rates were compromised after blastocyst freezing. Introduction of new systems for extended culture, the tendency towards single-blastocyst transfer, has radically changed human ART, but all the potential achievements were pending without a highly efficient blastocyst cryopreservation system.

For the oocytes, the strongest pressure was the rapidly growing market for oocyte donation, and legislation issues of several countries also required an efficient cryopreservation system to replace embryo freezing. Vitrification has offered a solution for both; by applying the right technology, survival rates approached 100% and further developmental rates were not compromised compared with the fresh controls.[3,20,21]

A kind of mitigated chain reaction has formed involving more and more clinics. Informal personal contacts played a more important role than papers and conferences. Publications arguing for widespread application of vitrification were widely criticized, but the flow of data was unstoppable, and suddenly the modest advancement in application turned to an exponential growth, where countries such as Latin America and Asia played an even more important role than the many traditional strongholds of human ART, including Scandinavia, Britain and France.[22]

An unexpected but very positive consequence of this competition was the exploitation of the hidden reserves of traditional freezing. With slight adjustments of methods, but without modifying the principles, the efficiency increased dramatically, and some parameters also approached the level of vitrification after oocyte and blastocyst cryopreservation.[23,24] Accordingly, the game is not yet over, and the winner of this competition will not just be either of the approaches, but all of the clinicians and patients in the field of assisted reproduction.

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