Freezing your baby’s cord blood, to be stored for an indefinite amount of time, is a fascinating process. There are various methods available depending on your company of choice, all with their advantages and disadvantages. Here is a summary of the most popular processes:
After the collection, which happens directly after the birth, your baby’s cord blood unit is shipped to the lab. Depending on the company you choose, it may then be processed to remove the red blood cells, or kept whole. Either way, the unit will be cryo-preserved, which means that a chemical additive is added to the cord blood so that the living cells survive the freezing process. Some of the most commonly used chemicals are pentastarch, hetastarch and dimethyl sulfoxide (DMSO). In Canada, hetastarch is not permitted for use due to its toxicity. It is a good idea to know which preservative will be added, since this chemical would be present in any future transplant that your family may need.
Cord Blood Storage Containers
Your unit can now be stored in two different types of containers—a cryo-bag or a cryo-vial. When cord blood was first stored, vials were typically used, but now airtight bags are considered the safer method of storage. This is because the older, vial-based method increases the potential of seepage of liquid nitrogen in and out of the screw-top lids of the vials, a concern especially in liquid phase storage (which we’ll address next). Additionally, vials are not a closed system, meaning cells can be exposed to contaminants during processing. Although the cryo-bags have been shown to be a superior method, the vials are still being used by some companies, so this is an important topic to address when signing on with a program.
Your cord blood, in whichever type of container, will be slowly cooled to between -90 and -130 degrees Celsius, and then added to a nitrogen tank which will keep the cord blood frozen at around -196 Celsius. Computer systems typically monitor the initial cooling process, as well as the temperature of the nitrogen tanks. This is a key aspect of the process because the unit must be frozen slowly enough to preserve the cells, and then maintained at very low temperatures if it is to remain viable.
Liquid vs. Vapor Nitrogen
Once down to -90 C the sample will be stored in a tank of nitrogen. And herein lies another variation—the nitrogen can be in vapor or liquid form. Because units are stored in tanks holding hundreds of other stem cell units, storage in vapor, though more expensive, is generally preferred and is becoming the industry standard. Vapor storage eliminates the risk of potential cross-contamination that exists in cord blood banks where all units are bathed in the same liquid. In recent years, vapor storage was risky because nitrogen is difficult to keep at low temperatures in vapor form, however new freezing technologies are now able to maintain the vapor consistently low at cryogenic temperatures. These temperatures are now monitored by computer to ensure the safety of the sample.