Vitrification is the standard method for embryo and oocyte cryopreservation in UK IVF laboratories, but the word itself – which comes from the Latin vitreum for glass – tells you surprisingly little about what is actually happening at a cellular level. Understanding the process helps both patients and new embryologists appreciate why the consumables and protocols used matter so much.
Step 1: Equilibration
Before the embryo or oocyte can be cooled, it needs to be prepared for the process. The cell contains water, and water forms ice crystals when frozen quickly – which would tear the cell apart. The equilibration step replaces most of that intracellular water with a cryoprotectant solution. The embryo is placed in the equilibration solution, which gradually diffuses into the cell while water moves out. This typically takes around 10 to 15 minutes depending on the protocol and the developmental stage of the embryo.
Step 2: Vitrification Solution
The embryo is then transferred to a vitrification solution – a higher concentration cryoprotectant mix. The timing here is critical and short: typically 60 to 90 seconds, no more, because the vitrification solution is cytotoxic at room temperature if the embryo is exposed to it for too long. The embryologist works quickly and precisely.
Step 3: Loading and Plunging
The embryo is loaded onto the carrier device – this might be a CBS high security vitrification carrier or another approved system. It is then plunged directly into liquid nitrogen at -195.8°C. According to ASRM best practice guidance, cooling rates exceed 10,000°C per minute. At this speed, there is no time for ice crystals to form. The intracellular fluid vitrifies – it transitions directly from liquid to a glassy, amorphous solid state without crystallisation.
Step 4: Storage
The carrier is transferred to a storage vessel and placed in the canister system. From this point, provided temperature is maintained, the embryo is biologically stable indefinitely.
The entire active vitrification process – from equilibration to plunging – typically takes around 15 minutes for an experienced embryologist. The skill is in the timing and the speed of the final steps.
The CBS High Security Vitrification Kits contain the equilibration solution, vitrification solution and carrier devices needed for the complete protocol. For further guidance, use CryoGPT or contact our team.
