Ovum Cryopreservation (Egg Freezing): How It Can Be Preserved to Be Used Later.

Ovum Cryopreservation (Egg Freezing): How It Can Be Preserved to Be Used Later.

Egg freezing is a procedure that involves preserving the fertility of women with the intention of usage at a later date. The woman’s eggs are collected and frozen to be used in fertility treatment. Naturally, the rate of conception in women reduces with age due to the drop in quantity and quality of a woman’s eggs. It is then advised that the process is most viable in young women because their eggs at this stage are of the highest quality. Prior to the commencement of the egg cryopreservation process, the embryologist at egg preservation fertility Arizona removes the surrounding cells on the egg so as to make a more informed evaluation regarding the maturity stage of the egg. Once the mature eggs are identified, the embryologist exposes each egg to concentrated levels of cryoprotectants. This substance ensures that no ice crystal forms on the egg cell during the cryopreservation process. 

Fertility treatment center Scottsdale utilizes numerous processes so as to attain success in egg freezing. Some of the processes involved in egg freezing include vitrification and slow freezing. The center uses the vitrification process to preserve egg/embryos from both their patients and donors. 


Vitrification is the most popular embryo and egg freezing technology. The process converts a crystalline structure into a smooth structure. Once the cells are frozen in the lab, the key focus of the entire process is avoiding the formation of ice crystals as the fluid in the cell is subjected to freeze to subzero temperatures. There are two negative effects that could result from the formation of ice crystals on the cells. One of the problems with the formation of the ice crystal is from the fact that it could act as a sharp razor. The crystal has the potential of shredding the cell membrane, which could kill the cell. The other problem is that in case the water in the cell was to turn into ice, it will then expand in volume, which could lead to rupturing of the cell. In an attempt to eradicate the formation of ice crystals, the processes developed should give room for the cell to freeze without the formation of ice. The vitrified embryos are 5-10 times exposed to cryoprotectant in comparison to slow frozen embryos. There is a tremendous reduction of fluid surrounding a vitrified embryo in comparison to slow frozen embryo. 

Components of vitrification

The process comprises three essential components. The first includes the exposure of crucial high concentrations of cryoprotectants to the embryos allowing swift cell dehydration. The second component involves loading the embryos in straws, which facilitates ultra-rapid cooling. The third step entails cooling the straws at the rate of thousands of degrees per minute. The embryo vitrification protocol takes a duration of 10 minutes in the laboratory. After removing the embryos from the incubator, it is then exposed to an equilibrium solution for 8 minutes so as to commence the dehydration process. It is during this process that the embryos are then introduced to the vitrification solution for 60 seconds. The embryos are then loaded into the straws and then put into -196 ˚C liquid nitrogen. The tiny straws enhance cooling to -196 ˚C from a room temperature of 25 ˚C in a duration of 2-3 seconds cooling at a remarkable rate of 4420 to 6630 ˚C/minute. The high rate of cooling used together with cryoprotectants makes the content in the straw appear as glass instead of ice. Lack of ice formation helps in protecting the embryos, as well as ensuring a 90% survival rate. 

Once the patients are ready for their vitrified eggs, the reverse of the above process is conducted. The process allows the warming of the frozen embryo back to room temperature, and the process gives room for rehydration. The warming of the embryo takes a duration of 20 minutes. After the embryo attains 37 ˚C, it is put in the incubator in the laboratory.       

Slow Freezing

In 1984, the first successful freezing of human embryos was conducted in Australia. The freezing process was referred to as slow freezing. The process involved cooling the embryos at a rate of 0.3˚C/minute, which continued until the temperature was below -30 ˚C. The frozen embryos were later stored in -196 ˚C liquid nitrogen up until thawing time. The procedure helped in eliminated the presence of ice crystal through the utilization of embryos incubation in cryoprotectants. The substance drew water from the cells in the embryo prior to the freezing of the embryos. 

Cyoprotectants draws water from the cell through the process of osmosis then crosses the cell membrane to replace the lost water. The placement of embryo in the mild solution of cryoprotectants makes the embryo to slightly shrivel after losing the water. It then regains its size once the cryoprotectants work in the cells. The small quantity of water molecules in the cell leaves the cell quickly in comparison to the rate at which the water leaves the larger cryoprotectant molecule, which takes longer to leave the cell membrane. The most commonly used cryoprotectants used during slow freezing include glycerol, propylene glycol, and ethylene glycol.

Limitations of Slow Freezing

The main limitation of this process is from the fact it was not reliable in freezing the unfertilized eggs. This led to the development of other methods that would ensure successful freezing of eggs for a duration of 25 years. Despite their attempt to improve the process, the process was never successful. The human egg has stubbornly resisted numerous efforts of slow freezing due to its large surface area to volume ratio. Another barrier to slow freezing is the delicate nature of the egg during ovulation due to reduction of DNA content as the egg prepares for the arrival of the sperm, which is expected to introduce new DNA. The ultra-sensitive nature of the egg due to chemical exposure and temperature variations is also another major problem affecting the freezing duration of the egg. 

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