Embryo storage sits at the heart of every IVF laboratory’s clinical responsibilities. Your storage system holds real patients, real treatment cycles, and in many cases years of difficult fertility treatment. Getting cryogenic storage right is not optional. It is a fundamental clinical obligation.

This guide covers everything IVF laboratories, embryologists and fertility clinic managers need to know.

Why Liquid Nitrogen Is Used for Embryo Storage

Liquid nitrogen sits at minus 196 degrees Celsius at atmospheric pressure. At this temperature, all biological processes stop completely. Cellular metabolism halts, enzymatic activity ceases, and the embryo enters a state of suspended animation. Importantly, it stays there indefinitely without any loss of viability.

No other widely available substance offers the same combination of extreme cold, physical stability and biological inertness. This is why liquid nitrogen is the universal choice for long-term embryo storage.

Vitrification vs Slow Freezing -Which Method Should Your Lab Use?

Before embryos enter long-term storage, your team must cryopreserve them using one of two methods. Understanding the difference matters because the two methods produce very different outcomes.

Slow freezing uses a controlled rate freezer to cool embryos at 0.3 to 2 degrees Celsius per minute. Cryoprotectant solutions are introduced gradually to minimise osmotic shock. However, ice crystal formation remains a risk at this cooling rate. As a result, post-thaw survival rates with slow freezing average just 50 to 60 percent.

Vitrification, by contrast, cools embryos at over 15,000 degrees Celsius per minute. Ultra-high concentrations of cryoprotectant solution are used alongside direct plunging into liquid nitrogen. At this speed, ice crystal formation does not occur at all. Instead, the cell contents solidify into a glass-like state. Consequently, post-thaw survival rates with vitrification consistently reach 80 to 95 percent in accredited IVF laboratories.

For most IVF laboratories today, vitrification is the default approach. The storage requirements in this guide apply to both methods, but the loading and preparation steps before the embryo enters long-term storage will differ depending on your laboratory protocol.

Embryo Storage Containers – What Goes Inside the Dewar

Good organisation inside your cryogenic storage system is essential for sample security, traceability and safe retrieval.  A standard embryo storage system inside a liquid nitrogen dewar uses a four-level hierarchy of containers. Each level plays a specific role.

Straws

CBS Embryo Straws are available in 0.15ml and 0.3ml capacities and are the standard clinical choice for IVF embryo storage. They provide a sterile, sealed environment throughout vitrification, storage and warming. In addition, they carry clear identification labelling for full chain of custody traceability.

Shop CBS Embryo Straws

Goblets

CBS Daisy Goblets are designed specifically for high-density straw storage inside cryogenic dewars. Their design maximises the number of straws per goblet while also allowing easy visual identification and safe retrieval without disturbing adjacent samples.

Shop CBS Daisy Goblets

Canisters

Canisters hold multiple goblets and slot into the dewar’s internal rack system. The canister is the unit your team raises and lowers into the liquid nitrogen when accessing samples.

The Dewar

The dewar is the outer vessel. It holds the liquid nitrogen and maintains the minus 196 degree Celsius environment for everything inside it.

This four-level hierarchy -straw, goblet, canister, dewar -is the standard architecture of a clinical embryo storage system. Every component must be clearly labelled and logged in your laboratory’s sample management system.

Monitoring and Alarm Systems for Embryo Storage

The minimum requirements for clinical embryo storage monitoring are as follows. First, continuous liquid nitrogen level monitoring for each individual storage vessel. Second, audible and remote alarms triggered by low LN2 levels or temperature excursions. Third, out-of-hours alarm coverage with a clear documented escalation procedure. Fourth, regular manual LN2 level checks as a backup to automated monitoring systems.

In addition, cryogenic data loggers provide an extra layer of assurance. They record temperature data over time and produce documentary evidence of storage conditions for regulatory audit purposes.

Safe Handling When Accessing Stored Embryos

Retrieving embryos from liquid nitrogen storage demands care, appropriate PPE and a clear protocol. The goal is to minimise both sample risk and staff risk simultaneously.

• First, always wear cryogenic gloves rated for LN2 exposure, a full face shield and a laboratory coat when accessing storage vessels. Never lean directly over an open dewar. The nitrogen vapour rising from the vessel displaces oxygen rapidly at face level.
• Second, work as quickly as possible once the canister is above the liquid nitrogen level. Samples begin warming immediately after leaving the liquid nitrogen environment. Most protocols specify a maximum time above the liquid surface before the canister must return to storage.
• Third, never allow samples to warm above minus 130 degrees Celsius during retrieval unless they are transferring immediately to the warming protocol. Recrystallisation can occur between minus 130 and minus 60 degrees Celsius and causes cell damage equivalent to a failed freeze.
• Finally, the Health and Safety Executive provides detailed guidance on cryogenic liquid handling in laboratory environments. All staff working with liquid nitrogen storage systems should complete training and demonstrate competency before working unsupervised.