Cryopreservation means preserving cells and tissues in live condition at low temperature, that all cell metabolism come to a standstill. Today, cryopreservation of surplus embryo has become a routine practice in ART and frozen embryo transfer has become an integral part of modern ART practice. It is also called sperm, eggs and embryos on ice. The main theory of cryopreservation is cells are stored at -196 degree Celsius . At this temperature no physiological process takes places meaning that cells can be stored almost indefinitely.
Indications of cryopreservation
-To decrease the chances of multiple pregnancy.
-To avoid the risk of Ovarian Hyper Stimulation Syndrome after oocyte retrieval.
-Postponement the embryo transfer in cases of poor endometrium due to various causes.
-To update the synchronization of endometrium and the embryo quality.
-Postponement of ET in poor responders.
-To preserve the reproductive potential of a female prior to radiotherapy, chemotherapy or ovariotomy.
-If embryo cannot be transferred during fresh cycle due to medical or technical reasons.
-Couples who wants to delay to have a child birth for few years due to various reasons.
The term use here is cryoprotactants which is either permeable or nonpermeable and are used usually in a mixture for slow freezing method or virtification. They protect the cells from cryoinjuries, stabilize intracellular proteins, lower the intracellular water freezing point and most importantly they reduce or eliminate lethal intracellular ice formation.
To decrease the toxicity of cell, the permeable cryoprotactants are ethylene glycol and dimethyl sulfonate, recently sucrose become standard component in virtification solution which is nonpermeable cryoprotactants.