“Universal” warming is a new concept we are hearing more and more that endorses the idea that any combination of different vitrification and thawing media will provide identical outcomes. Is this true and is it really worth the risk?

Vitrification and warming procedures handle human specimens. Patients all around the world put their trust in us to fulfill the dream of having a baby. Therefore, we have the huge responsibility to do everything in our hands to guarantee the best outcomes, which is a human life. Every time we handle a human specimen in our laboratory, we should ask ourselves a simple question: “what would I do if this embryo was mine?”
Kitazato’s outstanding results over more than 10 years, with a survival rate over 90% for oocytes and 90% for embryos, prove our determination to take care of each specimen.

Following the protocol versus universal warming. Are all vitrification systems really the same?

Different vitrification protocols are designed taking into consideration different aspects such as composition of the media, cooling and warming rates, specific characteristics of each vitrification device, procedure temperature, media volumes, etc., in order to achieve the best outcomes.
Mixing different media or switching from one vitrification protocol to another is neither good praxis nor validated, as it might contravene the Instructions for Use of both, or at least one, of the brands used for vitrification or warming and certainly does not guarantee good results. Furthermore, this approach is non-compliant with the Medical Devices Directive and the review and approvals from the notified bodies and health authorities, which means the user bears all the risk and responsibility in case of any adverse situation.
Both manufacturers and laboratory operators have the obligation to perform and follow a simple and safe protocol, with stable and reproducible results. These results should be monitored with KPIs ranging from vitrified specimen survival rates to live newborn ratios and are only guaranteed when following the protocol, there are no tips and tricks with proven efficacy to alter it.

Importance of scientific studies

“Universal” warming is currently supported by only one study that compares the results obtained mixing different media and protocols with results obtained by respecting the manufacturers’ indications approved by health authorities. Yet, there are hundreds of scientific studies over the years that demonstrate that following Kitazato protocol ensures the best clinical outcomes. The more clinical studies that support a product or protocol, the more certainty of success the laboratory will have.

Importance of the warming step

It has been scientifically proven that warming rates are a crucial factor in the cryopreservation process, even more important than cooling rates. Kitazato provides the best Cooling and Warming Rates on the market, which leads to the best survival rates.


These outstanding rates are the result of the perfect combination of Kitazato media composition, a precise protocol and, most of all, the design of our unique vitrification device: The Cryotop® which consists of a thin strip attached to a plastic handle that allows the loading of up to 4 specimens. Its design, together with an appropriate volume of media used during the procedure, enables the Cryotop ® Method to achieve the highest cooling and warming rates of the market.

Furthermore, despite what “universal warming” suggests, breaking the Cryotop® Method, using a different medium for the warming step, would mean losing the benefits provided by Kitazato vitrification media during the first step of the protocol.

Importance of warming and media composition


Different media from different manufacturers may look the same, but they are not, even though designed for the same purpose. There are remarkable differences such as HPC versus HSA, Trehalose versus Sucrose and, moreover, each medium contains different concentrations of cryoprotectants as well as a large number of essential and non-essential amino acids.


The combination of Kitazato cryoprotectants: DMSO, EG and Trehalose; together with HPC are used to increase viscosity, increase the transition temperature and reduce the level of toxicity. These factors, in addition to the highest cooling and warming rates provided by Kitazato vitrification media, increase the probability of success that is a healthy newborn child.

Cryotop Method

It is worth mentioning that Kitazato is recognized as one of the pioneering brands in driving and improving vitrification, which makes Kitazato the world leader in cryopreservation of human specimens. The Cryotop® Method is the most widely used vitrification protocol in the world, applied in more than 3,000 clinics and banks and in more than 2.500.000 procedures annually.
This means that most specimens all over the world are vitrified with Kitazato, and these should be warmed with Kitazato, as indicated in the Instructions for Use. This is what we strictly recommend and what scientific studies and health authorities endorse.
In science, everything counts, not everything goes.
Choose Science. Choose the Cryotop® Method.