Our Cryopreservation Security System

Cryopreservation security at a glance

• Tennessee Reproductive Medicine stores patients’ frozen eggs, embryos and sperm in a cryopreservation system in our IVF lab that we continuously evaluate and monitor to avoid any failure in our system that could result in damage to the precious specimens in our care.
• With the well-publicized failure of two fertility clinics’ cryopreservation storage systems in March of 2018 and the subsequent loss of patients’ stored embryos, eggs and sperm, we want to reassure our patients that we have a rigorous safety system in place to prevent failure of our system.
• Our cryopreservation safety measures include routinely scheduled inspections and monitoring systems with backup power supplies that provide the best possible safeguards for the secure storage of frozen eggs, embryos and sperm.
• No medical system or procedure that relies on technology can ever be 100 percent guaranteed to be problem free, but we’ve made our cryopreservation system as secure as possible.

How Cryopreservation works

Cryopreservation is the freezing and continued storage of tissues, which in the case of reproductive medicine include female eggs, male sperm and embryos created through in vitro fertilization (IVF). Eggs, embryos and sperm that are frozen to be used in future IVF or insemination procedures are cryopreserved until the patients are ready to achieve pregnancy. Freezing these items used to only be done using a slow-freezing method, and that is still used in many instances. But following continual advancements in these procedures, the “freezing” of eggs and embryos is accomplished most of the time using a rapid freezing process called vitrification, which is described below.

Why we use vitrification

The human egg is mostly water, which when slowly frozen creates ice crystals that can damage cells of the egg. That reduces the egg’s chance of surviving the freezing and thawing process and if it does survive, makes it more difficult to achieve a successful pregnancy with IVF. Vitrification typically does not damage the egg. Special chemicals called cryoprotectant agents are used to protect the cells in an extremely rapid freezing process. This does not result in ice crystals and solidifies the egg’s cells in a safe, glass-like state that preserves their integrity.

The laboratories TRM employs for this process use a variety of cryoprotectants and adjust the vitrification steps depending on the specimen being vitrified. The same adjustments can be made in the slow-freezing process, too.

The culture media system that protects the eggs during the freeze/thaw process is also much better now. This culture media is a liquid that supports the growth and health of cells and micro-organisms. In fertility medicine the culture media plays a major role in embryo development and can even influence the health of the resulting child.

Embryologists also must know exactly how eggs and embryos were vitrified in order to properly warm them back from their freeze-suspended state. The media dehydrates eggs and embryos in the freezing process and helps the egg during the warming process to rehydrate safely.

Embryos and sperm have much smaller cells than do eggs, so they are much less likely to have problems with ice formation. That’s why using frozen embryos was more successful in the past for IVF transfer to the womb than were frozen eggs. That’s changed, and vitrification is now the preferred process for freezing eggs and embryos.

The storage aspect of cryopreservation

A key element is maintaining these reproductive items in secure, proper storage. Once frozen, we store eggs, embryos and sperm in liquid nitrogen (LN₂) that maintains a temperature below -196º Celsius (-321º F). That is the boiling point of LN₂, and when the liquid reaches that temperature, it evaporates into gas.

The specimens are in tubes, called canes, that our embryologists place in storage tanks called dewars (named after the inventor Sir James Dewar). These waist-high, stainless-steel cylinders are like extremely high-grade thermos containers.

The inside of the dewar has two layers of material that do not conduct much heat, with a vacuum between them. The canes with eggs, embryos and sperm are sealed inside the dewar. The LN₂ naturally maintains its temperature without the need for any additional cooling mechanisms that would require electricity.

We don’t really know how long items can be effectively preserved, as not enough time has passed since cryopreservation began being used in reproductive medicine to determine that. But in 2017 an embryo frozen for 25 years resulted in a successful birth.

How we secure our cryopreservation system against failure

No system that relies on technology can be 100 percent guaranteed to never fail or experience problems. That applies to space travel, smartphones, thousands of medical procedures and cryopreservation.

But the field of fertility medicine, which includes the dedicated doctors and laboratory staff within our practice, diligently works on securing the cryopreservation system to make it as safe and secure as possible. This involves continuously improving the integrity of the equipment, the monitoring protocols to alert us of a potential problem, and the processes of cryopreservation and IVF lab protocols.

Our IVF lab is separated from the rest of the facility by an air lock and has a specially-controlled environment. Lab directors Amy Jones and Shan Wilkinson have implemented laboratory procedures in compliance with the College of American Pathologists’ requirements. Our lab directors make sure lab staff members are well trained on the latest procedures and established best practices for cryopreservation security.

Dewar cryostorage protocols

• The level of our supply liquid nitrogen (LN₂) tank is checked daily and re-ordered when low, usually every two weeks.
• The level of LN₂ in each storage dewar is measured, recorded and topped off three times a week, because liquid nitrogen within a storage dewar routinely evaporates at the rate of about an inch a day.
• These weekly checks allow us to monitor the evaporation rate of each tank and can lead to clues of potential tank failure if the evaporation rate increases.
• We immediately retire and replace a dewar if the evaporation rate does rise.
• Lab staff visually inspects dewars daily; a dewar that has lost vacuum integrity will be covered in frost and there will probably be localized flooding of condensate. An alarm would also have been triggered (see below).
• Lab personnel do not overfill dewars into the neck region, as this can cause damage.

Cryopreservation monitoring system

Since LN₂ naturally remains at -196º C, it requires no power supply to maintain items in a deeply frozen state. However, the monitoring systems we use do require power. Following are the steps we take to secure that vital system.

• When we are filling the tanks, we check the Cryosave probe for each dewar. Cryosave probes monitor the internal tank temperature, if the tank temperature drops to -150º C an alarm is triggered.
• Tennessee Reproductive Medicine’s laboratory is equipped with a Sensaphone unit that dials out to lab personnel if an alarm event occurs, and continues calling a phone tree of staff and doctors until it makes contact.
• All incubators feed into the Sensaphone, as does the Cryosave unit, which has probes in the lid of each liquid nitrogen dewar.
• Both the Sensaphone and the Cryosave are powered by a special supply of electricity delivered to special outlets in the IVF and andrology laboratory, which are connected to an emergency natural gas power generator.
• The generator performs weekly self-tests, and we perform maintenance quarterly.

How we respond to an alert

• Quickly assess if any tank has condensation on the outside.
• Measure the amount of LN₂ present in the tank(s) with the measuring stick located on the countertop above the tank.
• Fill the handheld dewar with LN₂ from the large dewar in the tank room and use this to fill the tank in question.
• Do not fill past the bottom of the neck of the tank.
• By filling the handheld dewar again, it can be used as a temporary holding vessel to quickly transfer canes of sperm, eggs and embryos. Then they can be quickly transferred into one tank where they can be held temporarily while the integrity of the other tank is being evaluated.
• Contact a lab director as soon as possible if specimens are affected.

By developing and strictly adhering to our safety protocols, we are confident we are doing as much as humanly possible to safely secure our patients’ preserved eggs, embryos and sperm. We take the trust our patients place in us by putting the future of their families in our care as a tremendous honor and responsibility.