Cryopreservation System Safety
Cryopreservation system safety at a glance
- University of Colorado Advanced Reproductive Medicine (CU ARM) understands that frozen eggs, embryos and sperm are the building blocks of our patients’ future families. We adhere to rigorous safety measures in our cryopreservation system to provide the safest possible storage for our patients’ specimens.
- We use a 24-hour monitoring process with an automated phone tree notification system that alerts staff in the unlikely event that one of our cryopreservation units malfunctions, while continuously monitoring temperature as well as connectivity of the alarm system. The systems are connected to uninterruptible power supplies (UPS) as well as backup battery power.
- Failures of cryopreservation systems throughout their use by in vitro fertilization (IVF) labs are rare, though two recent cases (March 2018) have raised attention.
- Though no system reliant on technology provides 100 percent prevention of failures, CU ARM has never lost one egg, sperm specimen or embryo our patients have entrusted to our custody due to cryopreservation tank failure. In fact, we have never had a failure in any of our cryopreservation tanks in any location.
- Patients who have further questions after reading the information below can contact our IVF lab by email: [email protected].
How cryopreservation works
In fertility medicine, cryopreservation is the freezing and storage of eggs, sperm and embryos that are being preserved by individuals and couples to achieve pregnancy through assisted reproductive procedures in the future. The freezing process for eggs and embryos has changed significantly in recent years, moving from a slow-cooling method to the vitrification method that rapidly solidifies the specimen into a stable, glass-like state. Although vitrification is technically different from freezing, we will refer to both slow-cooling and vitrification as freezing in this document.
The human egg consists mostly of water, which causes sharp ice crystals to form during the slow-cooling method and poke holes in the cell membrane, which kills the cell and results in low overall survival rates.
In contrast, vitrification uses high levels of cryoprotectants and ultra-rapid cooling rates, which solidifies the medium containing the egg to a glass-like consistency while avoiding ice crystal formation and membrane disruption. This process has significantly superior survival rates after warming compared with slow-freezing. The widespread adoption of vitrification was thus hugely important to the practice of egg freezing. Egg vitrification survival in our lab at CU ARM is well over 90 percent!
Embryologists must know exactly how a frozen egg was vitrified in order to successfully warm it back to life, so to speak, as each vitrification procedure has a distinct warming protocol that needs to be followed to ensure optimum survival.
After they are frozen, eggs, sperm and embryos are stored in a cryopreservation vacuum tank, called a dewar after its Scottish inventor Sir James Dewar. Cryogenic storage dewars are filled with liquid nitrogen that has a boiling point much lower than room temperature (-196 °C or -321 °F). These dewars maintain the low temperature environment that protects the specimens’ integrity in the frozen state for an indefinite amount of time.
For example, an embryo frozen for 25 years resulted in a pregnancy and successful birth in 2017. The field of cryobiology is relatively new and even newer in its fertility applications, so there is limited data for frozen eggs, sperm or embryos stored long-term before establishing pregnancy.
How we keep our cryopreservation storage system safe
The essential aspects of our cryopreservation safety system are integrity of the storage dewars, a reliable and redundant power source, diligent monitoring and effective communication if/when a compromise were to occur.
Dewar cryogenic storage
Safely keeping frozen eggs, sperm and embryos is primarily about maintaining -196º C in the cryostorage dewar container. A cryogenic storage dewar is like a very sophisticated, science-grade thermos. It’s a waist-high, cylindrical stainless-steel container with heavily insulated sides, bottom and lid. It consists of two layers of material that conduct little heat with a hard vacuum between them. The embryos, eggs and sperm are sealed inside.
If the temperature rises above -196º C, liquid nitrogen starts to boil and turn into gas. Even with the dewar lid sealed, the surface of the liquid nitrogen inside naturally evaporates at the rate of about one inch a day. So the dewar containers have to be routinely re-filled. Though auto-fill dewar systems exist, CU ARM does this manually to ensure that no filling malfunctions occur.
To ensure integrity of our cryogenic storage dewars, we periodically inspect each dewar and measure evaporation rate to determine if the dewar functions to the manufacturer’s specifications. There is no universally established lifespan for a dewar, but we monitor functionality of each dewar routinely and replace any dewar that is not performing to the manufacturer’s specs. Furthermore, we use only the highest quality dewars from trusted manufacturers. They are fully tested before any specimens are added for cryostorage.
We also have extra liquid nitrogen supply tanks on hand at each lab and additional emergency cryostorage space should we ever need to move specimens from a failing dewar.
The dewar tanks themselves don’t require electricity to keep the specimens at -196º C, because that’s what the liquid nitrogen does. No cooling comes from an electrical power source. But the monitoring and alarm system does use electrical power.
At our IVF lab and our Stapleton andrology lab, the dewar alarm system is connected to a UPS. These prevent small power interruptions and can maintain constant power to the alarm system for several hours after a power failure. Each dewar has a temperature probe connected to the alarm system that continuously monitors the temperature.
Should the power on the UPS run out, the alarm systems have additional backup batteries. Should both the battery and UPS power run out, the system at our IVF and Stapleton labs will initiate our calling tree to notify us that the unit is out of power. The IVF lab’s UPS is on the hospital’s emergency power system, making the interruption of power there highly unlikely.
Our cryogenic storage dewars at the Colorado Springs lab use an Accsense monitoring system that notifies us in case of a power failure or storage dewar failure by continuously pinging the system and taking temperature measurements. The Accsense is a data logger system that utilizes wireless and internet technology to record input data over time. Accsense is powered through the data cable.
As described above, all long-term cryostorage dewars at all our lab locations are monitored 24/7 by a sophisticated alarm system. The alarms are tested on a weekly basis to make sure they are working properly. For eggs, embryos and sperm at the IVF and Stapleton labs, we use a Sensaphone system. At our University of Colorado Hospital (UCH) lab, the alarm system is on the hospital’s emergency power system.
Once a week we test the alarm, either via temperature disruption or through other equipment connected to it. Twice a year, each dewar probe is tested individually to ensure it is working properly. When any temperature probe measures a temperature out of range, an alarm is initiated internally. If nobody is at the lab to acknowledge and cancel the alarm, a calling tree is initiated.
Our Colorado Springs lab uses the Accsense system described above. It is tested once a week by temperature interruption. Accsense is also continuously pinged to make sure there is connectivity. It takes temperature measurement at a specified frequency and logs that data. In case the temperature goes out of range, there is a calling tree that calls lab personnel cell phones until acknowledged.
Should the building power fail and the data is down, it will initiate a calling tree to notify us that there is no connectivity, and thus the alarm is not active at that time. This call center is at the Accsense data logger location and not dependent on any phone or data lines.
At all of our labs, should we receive a temperature alarm after hours, one of the lab staff will go to investigate the reason for the alarm immediately and address the issue. Should it be connectivity loss or power failure, we will revert to manually checking the liquid nitrogen in the tanks twice a day until the alarm system has been restored.
Understanding limitations of cryopreservation safety
In this and many other areas of medicine that rely on technology, it is not possible to make a perfectly safe system. It is possible to make a system as safe as possible, which is what we have done at CU Advanced Reproductive Medicine. Our lab staff is well trained, experienced and dedicated to safely preserving our patients’ cryopreserved specimens.
Our IVF labs are certified and regularly inspected by the College of American Pathologists. Through their diligence and our own, we maintain the safest possible cryopreservation environment.
CU Advanced Reproductive Medicine has never lost one egg, one embryo or one sperm specimen entrusted to our cryopreservation care. We continually analyze and upgrade our security protocols, systems and laboratory equipment. Our lab personnel constantly learn new technologies and best practices, while refining their skills through clinical experience and shared information.
Our lab personnel are happy to answer any questions, and may be contacted by email at [email protected].