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Vitrification is the process of converting something into a glass-like solid that is free of any crystal formation.thus now a days vitrification is most commonly used freezing technique used in Fertlity clinic instead of conventional slow freezing.

Vitrification in IVF can allow freezing of spare embryos with better post-thaw survival rates and higher pregnancy and live birth rates from frozen embryo transfer cycles.

We started vitrification of embryos in our IVF lab in early 2007 and have seen excellent post-thaw embryo survival and substantially higher pregnancy rates after frozen transfer procedures.

The slow feezing method was very time consuming. Slow cooling was used (1 degree/min or less) to about - 80 degrees Centigrade. Then the embryos were placed in liquid nitrogen.

The embryos also needed to be thawed slowly and a cryoprotectant added and removed in many gradual steps. This was a lot of work.

The newer vitrification technique has prove to have equivalent success rates with human embryos transferred fresh or after freezing and thawing.


Cryoprotectants are used in the solution that the embryos are frozen in. There are 2 basic types - permeating (e.g. ethylene glycol ) and non-permeating (or extracellular) such as sucrose.

Cryoprotectants are useful because they:

  • Lower the freezing point and may prevent intracellular ice formation.
  • May protect cells by interacting with membranes as they change from a pliable to a rigid state.

Embryos can be frozen at the pronuclear stage (one cell), or at any stage after that up to and including the blastocyst stage (5-7 days after fertilization). Different cryoprotectants and freezing solutions and protocols are used for different stages of embryo development.

IVF clinics are currently doing all of their embryo freezing at the blastocyst stage. There has been a recent trend in the IVF world away from the traditional slow freezing method that has been used since the 1980’s. Vitrification for IVF embryo freezing is becoming a more widely used technology.

In our clinic vitrification of "spare" embryos after IVF is showing much higher "post-thaw survival" and pregnancy success rates after transfer.