Slow freezing versus Vitrification

Cryopreservation of sperm, egg and embryo could be done either by slow freezing or vitrification method.First of all, to know the difference between slow freezing and vitrification, we have to understand each mechanism individually.

What is slow freezing?

Slow freezing is a process of gradually dropping down the temperature below the freezing point to freeze the sperm, egg or an embryo. The sperm, egg or an embryo is placed in the container with liquid nitrogen solution and then gradual decrease of temperature below the freezing point is carried out.

What is Vitrification?

Vitrification is a process of freezing of sperm, egg or an embryo to form glass-like structure by dropping the temperature to -196 degrees abruptly. During the process, liquid nitrogen is used.


In slow freezing, due to gradual cooling chances of ice formation become higher. Ice formation is not good as it causes cracks within the sperm, egg or an embryo. It leads to death and hampers the growth of embryo.
Whereas, in vitrification, due to abrupt cooling chances of ice formation is almost negligible. Due to which, it is considered to be the best method for cryopreservation.
Slow freezing is an old method of cryopreservation which does not provide the favorable results. Therefore, vitrification is a technique that is practiced nowadays.
The IVF success rates are higher when vitrification is carried out instead of slow freezing method.


Vitrification is most preferred than slow freezing for cryopreservation.Nowadays, most of the fertility clinics in Delhi do not carry out slow freezing. They go for vitrification method as it is a modern technique which provides better results after cooling.At our IVF clinic, International Fertility Centre(IFC), we do not perform slow freezing and practice vitrification.

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