ABSTRACT
With conventional slow freezing, a process first developed by Whittingham et al.,1 embryos suspended in a solution containing a low concentration (1-2 mol/L) of permeating cryoprotectant are cooled slowly (0.3-0.5°C/min) before the sample is cooled with liquid nitrogen. This method, derived deductively by Peter Mazur, was proven effective and is now used routinely with the aid of a programmable freezer. However, it requires a long cooling stage and a machine for controlling the cooling rate. In addition, the formation of ice in the preservation solution can lead to intracellular ice forming, probably the biggest obstacle to the successful cryopreservation of embryos.
