Cryopreservation is the method of keeping the embryos, sperms, gametes, tissues from ovaries or testicles in an extremely low temperature with an intention of the use in future. Samples can be kept intact for the future use and there is a huge saving of cost and resources. There is increased efficiency and reduced discomfort and inconvenience to the couple.
We perform the task in two steps. Firstly, the sample is collected from the female or male partner and kept in special tubes that look like straws. These tubes are stored below zero degree Celsius temperature and there is a special solution used to prevent the specimens from getting frozen. This solution is called cryopreservant and the specimens are thawed before they are used.
There are multiple protocols for cryopreservation and they vary in terms of the storage temperature, type of cryopreservant, time required for freezing and thawing and the type of specimen
Use of cryopreservation
It is very obvious that there is an increase of efficiency with the help of cryopreservation. The embryos, sperms or matured eggs extracted once can be used later without having the hassles of extracting again. This saves great amount of time, energy and money. There is no need to go for the stimulation of the ovaries again and again. The woman gets relief from the physical discomfort multiple times.
Lower risk of hyper stimulation syndrome : It is a dangerous condition when ovaries are stimulated multiple times using medicines and it can cause death as well. If the process of IVF gets done multiple times and every time there is a stimulation of the ovaries to produce the egg, then it creates a lot of strain on the ovaries. Cryopreservation avoids it by using eggs that got extracted one time. In case of IVF, doctors used to implant more than one egg in order to increase the probability of success. With cryopreservation technique, it is not required to do so. Doctors can implant one or maximum two embryos in one attempt and keep preserve the others.
Preservation of the fertility : Interestingly, cryopreservation can be used to preserve the fertility for people who have threat of losing the same. For example, females with a history of early menopause or couples undergoing chemotherapy or radiotherapy have a risk of losing fertility early. In such case, they can preserve the embryo or sperm for later use.
How it is done ?
Cryopreservation is actually a process of freezing human tissues in such a way that they remain “live” for a long time. It means that there should not be any damage to the functioning of the cells so that they become active once again after thawing process. There are various protocols used to preserve the human tissues in extremely low temperature.
Types of Cryopreservation :
- Sperm Freezing
- Egg and Ovarian Tissue Freezing
- Embryo Freezing
How does Cryopreservation happen ?
Freezing protocols play the phenomenal role in the cryopreservation process. A freezing protocol is nothing but the method of freezing the tissues. It depends on what tissues we are preserving before selecting the protocol because every tissue has a different composition and therefore slow or fast protocol would depend on the tissues.
Slow protocol : In slow protocol we reduce the temperature gradually so that the reproductive tissues and cryoprotectants get cool down gradually. We add the cryoprotectants and start decreasing the temperature with a rate of minus two degree per minute until the temperature reaches minus seven degree Celsius. As soon as this temperature is achieved, the acceleration rate is reduced to -0.3 degree Celsius until it reaches -30 degree Celsius. The rate is again increased until the temperature goes to -135 degree Celsius and then finally tissues are stored in liquid nitrogen at the temperature of -196 degree Celsius.
Rapid protocol : We plunge the tissues directly in the liquid nitrogen and the temperature drops to -196 degree Celsius immediately. Very high concentration of cryopreservant is used to avoid crystallization of the cells.
Thawing protocols : It is more complex and critical to thaw the cryopreserved tissues to bring them to room temperature without getting damaged. Typically the straws containing cryopreserved tissues are placed in special water baths until the temperature rises to the room temperature. The cryopreservation medium is gradually diluted to avoid any kind of toxic effect.