The cryopreservation of eggs or embryos begins with undefinedvitrificationundefined or undefinedfreezing.undefined Vitrification is an ultra-rapid freezing process performed in our embryology laboratory, wherein the eggs/embryos are rapidly cooled to subzero temperatures. This rapid cooling process prevents the formation of ice crystals, which can cause cell damage.

The process of vitrification has three critical components. First, eggs/embryos are exposed to high concentrations of cryoprotectants to allow rapid dehydration of cells. Second, the eggs/embryos are loaded into tiny storage devices (usually straws) that will facilitate ultra-rapid cooling. Third, the straws containing the eggs/embryos are cooled as fast as possible, typically at thousands of degrees per minute.

In practice, this means that eggs and embryos are vitrified very quickly in the laboratory. A typical embryo vitrification protocol is complete in about 10 minutes. Embryos are removed from the incubator in the laboratory and exposed to an equilibration solution for 8 minutes to begin the dehydration process. After 8 minutes in equilibration solution, the embryos are moved into a vitrification solution for 60 seconds. Then, they are quickly loaded into straws and plunged into liquid nitrogen at a temperature of -196undefinedC. The tiny straw will cool from room temperature (about 25undefinedC) to -196undefinedC in two to three seconds, giving a cooling rate of 4420-6630undefinedC per minute.

This high cooling rate combined with the use of high concentrations of cryoprotectants allows the contents of the straw (embryos plus surrounding fluid) to turn to a glass like substance instead of ice. Avoiding ice formation in this way successfully protects the embryos from damage and allows them to be warmed later giving survival rates consistently above 90%.

For egg vitrification, the process is similar, but the exposure to the equilibration solution is slower, usually about 15 minutes, and it is broken up into 4 steps. This stepwise approach is designed specifically for the egg and achieves the same level of dehydration as can be obtained with embryos in a shorter time. These steps, however, are critical to the survival of the eggs and must be followed exactly. Moving the eggs into vitrification solution, loading and cooling the straws is the same as is done for embryos.

This high cooling rate, combined with the use of of cryoprotectants, allows the contents of the straw (embryos plus surrounding fluid) to turn into a glass-like substance instead of ice. Avoiding ice formation in this way successfully protects the embryos from damage and allows them to be warmed later, delivering embryo survival rates consistently above 90%.

When our patients return to use their vitrified embryos, the vitrification procedure described above is reversed to allow warming back to room temperature for rehydration. The procedure undefinedwarmsundefined the tissue in just 20 minutes, and it is placed back in the incubator at 37undefinedC in the laboratory. Embryos can be transferred back to the uterus immediately and eggs can be fertilized with sperm 3-4 hours later.