How does embryo cryopreservation work and what determines survival rate at thaw?
Embryo cryopreservation in UK IVF laboratories now uses vitrification in the vast majority of cases – a process that achieves cooling rates greater than 10,000°C per minute using high-concentration cryoprotectants to bypass ice crystal formation entirely. The result is a glass-like solid state that preserves membrane integrity and organelle structure more reliably than slow-freeze protocols, which remain in use for sperm and some blastocyst applications.
Survival rate at thaw is primarily determined by three factors: cryoprotectant loading consistency, the speed and precision of the warming step, and the quality of the storage environment during the intervening period. A temperature excursion above -130°C at any point between vitrification and warming – even for minutes – can cause recrystallisation that is undetectable at storage temperature but catastrophic on warming. Closed high security systems such as the CBS High Security vitrification kit eliminate direct liquid nitrogen contact during loading, which reduces contamination risk and is increasingly required by HFEA inspectors. Contact Cryolab for current stock and protocol support.
