What Is the Vitrification Warming Protocol and How Is It Performed Correctly in an IVF Laboratory?

The vitrification warming protocol is the procedure used to recover cryopreserved oocytes or embryos from liquid nitrogen storage, remove the cryoprotectants used during vitrification, and restore the cells to a physiological state suitable for transfer or further culture. It is the reverse of the vitrification process and requires the same level of technical precision, time-critical execution, and matched media as the initial freeze. Errors in warming are among the most common causes of poor survival rates in vitrification programmes, even when the original vitrification was performed correctly.

The warming process begins with the removal of the vitrification carrier from liquid nitrogen storage. The carrier is plunged immediately into the first warming solution at 37 degrees Celsius, maintained on a heated microscope stage or in a pre-warmed incubator. The high-concentration cryoprotectants in the vitrified specimen are diluted out in a stepwise series of warming and dilution solutions, each at a defined temperature and for a defined duration. When using the CBS High Security Vitrification Kit, always follow the specific warming protocol provided with the kit to ensure matched media performance.

These parameters are not interchangeable between different product brands, and using a warming protocol designed for one system with the media of a different system is a common cause of suboptimal outcomes. Every IVF laboratory should have a written, validated warming SOP specific to the carrier and media combination in use, and all embryologists must be trained to that specific protocol before performing warming independently.

Achieving consistently high warming survival rates of 90 percent or greater requires that warming solutions are pre-equilibrated to the correct temperature, the heated stage is calibrated before each session, and oil overlays are pre-equilibrated to remove volatile contaminants. Browse our certified vitrification and warming consumables including the CBS High Security Vitrification Kit for IVF embryology programmes across the UK.