Are my frozen embryos, eggs and sperm safe? A common question of the week:
The short answer is “yes” in most fertility clinics and storage facilities despite the recent major problems in two separate facilities regarding their storage tanks. Apparently, in both occasions, the storage tanks failed somehow or liquid nitrogen used to keep them cool evaporated. Whereas this is extremely sad and devastating, it is actually not a common occurrence due to safeguards in place in storage facilities.
At our facility, we fill out our cryo-tanks to the top at least once or twice a week even if they are not low on liquid nitrogen. Our experience has been that liquid nitrogen will evaporate over time no matter what, but if the tanks lids are opened and closed frequently for placement or removal of frozen tissues, evaporation will increase and frequent filling may be necessary.
The type of the tank is also important because evaporation will depend on the surface area of the liquid exposed to air as well as how long the lid is kept open. It’s also wise to divide up frozen samples in multiple tanks in the laboratory instead of using the “mega tanks”. Maintaining a durable tank is also important in the sense that if the tank has been used for many decades, it may be time to replace it with a new one. Even though these cryo-tanks feel as durable as literally a military tank, they are constantly exposed to extremely cold temperatures inside and room temperature outside and they are not immune to wear and tear forever.
It is important to have designated personnel in the laboratory to regularly check on the cryo-tanks and fill up with liquid nitrogen. It’s also a good idea to dip frozen tissues in liquid nitrogen and store that way instead of using the “vapor method” to keep them cool. If frozen tissues are stored in liquid nitrogen and kept in the bottom of the tanks, the risk of damage will be minimal even if the tanks are low on liquid nitrogen because it will take a very long time for the depletion of the liquid all the way to the bottom of the tank.
Last not least, all cryo-tanks should have an alarm system that can alert the laboratory staff of any changes in temperature inside the tanks. The alarm systems are typically designated to make an automated call with the first drop in the temperature or the level of liquid nitrogen allowing enough time for someone to check the tanks or the level of liquid nitrogen and fill up as needed. When frozen tissues are stored and kept cool in the vapor of liquid nitrogen, it becomes a bit more difficult to control and manage temperature changes. Nevertheless, good laboratory policies and close monitoring of the tanks are essential in maintaining frozen tissues in long term storage facilities and IVF laboratories.