The comparison between vitrification and slow-rate controlled freezing has largely been resolved in favour of vitrification for the cryopreservation of human oocytes and embryos in the modern IVF setting. Virtually every leading UK IVF programme now uses vitrification as the primary method for oocyte and blastocyst cryopreservation, and the evidence base for this choice is substantial and growing.
Slow freezing uses a programmatic controlled-rate freezer such as the CBS Digitcool Controlled Rate Freezer to reduce temperature at a carefully controlled rate, typically between 0.3 and 2 degrees Celsius per minute, through the critical temperature range before plunging to liquid nitrogen. In practice, some ice formation still occurs in oocytes particularly, because their large cell size and relatively low surface area to volume ratio makes water efflux slower and less complete.
Vitrification takes a fundamentally different approach. By using high concentrations of cryoprotectant and cooling at rates exceeding 20,000 degrees Celsius per minute through direct plunge into liquid nitrogen using a specialist carrier such as the CBS High Security Vitrification Kit, the biological material transitions directly to a glass-like solid state without any crystallisation. Published systematic reviews demonstrate oocyte survival rates above 90 percent with optimised vitrification protocols, compared to 60 to 70 percent with slow freezing. For blastocysts, vitrification shows survival rates of 95 percent or more in experienced programmes.
Explore our complete range of vitrification equipment and consumables and controlled-rate freezing systems including the CBS Digitcool for UK IVF clinics and research laboratories.
