What the 55 Year Storage Limit Means for an IVF Laboratory

Since 1 July 2022, UK patients can store eggs, sperm and embryos for up to 55 years, provided they reconsent every ten years. The consent paperwork changed quickly. The storage estate mostly did not.

Capacity planning is now cumulative

Under the previous ten year limit, storage largely cleared itself. Samples left at a rate that roughly matched intake and capacity was a rolling problem.

Under the current limit, samples leave as a trickle and the store accumulates. Any capacity model carried over from before 2022 will underestimate, and most units find on honest modelling that they need additional capacity sooner than their current vessel count suggests.

Vessels do not last as long as the samples

A vacuum insulated vessel does not last 55 years. The getter that maintains the annulus vacuum has a finite capacity, and once it saturates, performance declines without anything visibly breaking.

That means samples will outlive several generations of vessel, and transfer between vessels becomes a planned, repeated and documented operation rather than a rare event.

Every transfer is a warming risk, which makes the next section relevant.

The danger zone is colder than people assume

Below roughly -130°C, biological material enters the glassy state. Molecular motion effectively stops and degradative reactions cease. A blastocyst warmed after twenty years has the same biological age it had when frozen.

The risk band is between about -130°C and -80°C, where motion has resumed but the sample still looks frozen. Ice recrystallisation occurs there, it is cumulative, and it is invisible. A sample that spends thirty seconds too long in warm vapour during retrieval shows nothing.

Vitrification moved the risk rather than removing it

Slow controlled rate freezing cools at a programmed rate with a low concentration of cryoprotectant. Vitrification uses a very high cryoprotectant concentration and minimal volume, cooling fast enough to bypass ice formation entirely.

Vitrification has largely displaced slow freezing for oocytes and embryos. It is also far less forgiving of operator variation, because loading volume, exposure time and the interval before plunging are all operator controlled and measured in seconds.

Controlled rate freezers remain the method of choice where sample volume makes vitrification impractical, so a laboratory doing both needs both.

Open or closed carriers

Open carriers give the highest cooling rate through direct contact with liquid nitrogen. Closed carriers seal the sample before cooling, so cooling is slightly slower but there is no contact.

The argument is cross contamination, since liquid nitrogen is not sterile. Documented transmission in clinical practice is very rare, so the trade is a real reduction in cooling rate against a low probability risk.

Both positions can be defended. Not having decided, not having documented it, and not being able to justify it at inspection cannot.

Monitoring

In March 2018 two unrelated fertility clinics in the United States suffered cryogenic storage failures on the same weekend and thousands of eggs and embryos were lost.

Four things separate a maintenance job from an incident: continuous level and temperature monitoring, alarms that reach a person outside working hours, oxygen depletion monitoring for the people in the room, and a written escalation procedure that has been tested rather than filed.

Full article: https://cryolab.co.uk/embryo-cryopreservation-55-year-storage-limit/