What is Embryo Cryopreservation?
Embryos resulting from fertilization of eggs and sperms, both collected from parents, at laboratory settings are transferred to uterus of the mother.
However, maximum 2 embryos can be transferred in each cycle of vitro fertilization therapy. Other embryos can be frozen and stored in order to be used in subsequent attempts, if required. Thus, a chance of more than one pregnancy is obtained at once. Embryos can be stored up to 5 years pursuant to relevant Turkish legislation.
What Are Methods of Embryo Cryopreservation?
There are two common methods in embryo cryopreservation. These two methods are different from each other in protecting structural integrity of the cell.
Slow Controlled Freezing
In this method, cellular viability is assured by creating ice crystals around the cell during gradual cryopreservation.
Vitrification
In vitrification, a glass-like hard surface is created around the cell through rapid cooling with high-concentration solutions. In this way, viability is conserved.
Embryos frozen with any one of these methods are balanced with a special protective fluid, called cryoprotectant, and placed in special plastic containers. Cryopreservation can be performed at all stages of the embryonic development.
Embryos stored in liquid nitrogen at -196 C are transferred to a special culture environment for thawing. Transfer can be done within one day after this procedure.
When cryopreservation is successfully performed, it is expected that viability rate of embryos is around 70%-80%. Post-thaw embryo survival depends on certain factors like quality of embryo, cryopreservation phase and cryopreservation methods.
Why is Embryo Cryopreservation Done?
Embryos left after fresh embryo transfer can be used for future use. Thus, cost is reduced and maternal stress is alleviated, as oocyte pick-up will not be required again.
Embryo cryopreservation can also be applied if transfer is postponed due to a medical necessity.
As embryos are sensitive to cryopreservation, embryos may not have the same viability when thawed.