Slow freezing versus fast freezing

The cryostation of sperm and embryos has become a routine procedure in assisted human reproduction (ART). In current clinical practice, oocyte cryostation has also been introduced.
Currently, there are two cryopreservation techniques: slow freezing and fast freezing.

Slow freezing, used for the first time in 1986, has been the only method of freezing oocytes for more than 20 years. This technique consists of: balancing cells in a cryoprotective solution, slow freezing (up to -40 ° C), rapid freezing (up to -150 ° C) and transferring them to liquid nitrogen.

A decade ago, biologist Dr. Masashige Kuwayama and his collaborators developed one step vitrification protocols. Fast freezing is the newest method of cryopreservation, which uses a high concentration of cryoprotectants, which reduces the risk of ice crystals and cellular destruction.

The comparative studies between the two techniques have demonstrated the superiority of vitrification in the case of oocytes.

An article published in the journal Fertility and Sterility has shown that vitrification is an efficient, rapid and economical method for oocyte cryopreservation that offers high rates of survival, fertilization, embryonic development and normal pregnancies.Thus, vitrification is a viable alternative to the management of female infertility.

Another study found that the oocyte survival rate was significantly lower in the slow freezing group (61%) than in the vitrification group (91%) and that slow freeze was associated with higher rates of abnormalities oocytes.

Regarding the survival of vitrified vs. slow freezing embryos, research confirms the superiority of the vitrification method, both in the cleavage stage and in the blastocyst stage. These findings are confirmed by the results published by E.K. Kim, in 2015, on the survival rate of embryos at the stage of cleavage by the two techniques (the ratio being 90.2% for the vitrified embryos and only 81% for the slow freezing ones).

The IVF media provided by Origio and Sage, for the procedures detailed above, are the following:

a)  Vitrification:

Medicult Vitrification Cooling;
Sage Vitrification Kit.

Slow freezing:

Embryo Freezing Pack;
Quinn’s Advantage Blastocyst Freeze Kit;
Quinn’s Advantage™ Embryo Freeze Kit;
CSC Freezing Medium.


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