From our experience in working with many clinics throughout the world, there are special conditions in warming ova that make for a steep learning curve even if one has already worked with vitrification and warming of blastocysts. Although experience with vitrified embryos can reduce the learning curve for ova, we have found that the nature of the oocyte makes it less forgiving to variations in protocol and technology.
TWEB’s dedication to quality includes an instructional service called “verification” at the time of the clinic’s first patient’s oocyte warming. There is no charge for this initial verification service. Verification does not mean the embryologist is now approved to perform future ova warmings. That will need to be satisfied by the laboratory’s regular methods for technique approval. Verification though will allow us to present to your embryologists the various factors that might lead to problems in warming. Just as an embryologist would practice many sperm injections in order to be proficient, so should the embryologist work to perfect the technique on “extra” ova, before using the technique on a recipient’s ova.
The biggest problem we have seen is when the embryologist assumes warming ova is the same as warming blastocysts. Warming of vitrified oocytes is very time and temperature sensitive. It is critical that the warming solution (TS) be at 36-37 C. Prior to warming, one must validate the particular warming system being used. This is done by placing a vial with 1.5 ml of water into your warming system and after 30 minutes checking the temperature of the warming solution. It is not sufficient to check just the temperature of the incubator or water bath. Additionally, this temperature must be maintained for all three of the TS vials used for warming. Frequent opening and closing of some incubators used for warming could lead to the first vial of TS being at temperature and the following ones being below temperature. 1.5 ml of TS media must be prealiquoted into small tubes and must never be pipetted just prior to use or its temperature will decrease by as much as 4 C. Many suppliers like Cryotech provide the solutions in small tubes pre-aliquoted with 1.5 ml.
One of the difficult stages in warming is identifying (finding) the oocyte on the cryodevice or in the TS medium. The oocyte typically undergoes a change in appearance making them transparent and difficult to see. Because of this, proper set up of the stereoscope prior to warming is critical. For some scopes this means not only the proper magnification (about 12X to 15X), but also proper incident illumination and a diaphragm (if one is present) that is at 80% open (Kohler illumination).
Proper validation of the warming method, training of the embryologists and ongoing quality control of both The World Egg Bank system but also the clinic’s laboratory are critical to success. By doing this we can provide patients with a high probability for success