Oocyte cryopreservation- Shaambhavi Sharma

Oocyte Cryopreservation- Shaambhavi Sharma

Oocyte Cryopreservation is a technology where unfertilized eggs are extracted from the ovary, frozen and stored. These eggs can be later fertilised and used whenever she feels ready to be pregnant.
Oocyte is an immature female reproductive cell or gamete prior to fertilization; It is primary oocyte prior to completion of the first maturation division and a secondary oocyte in the 
period between the first and second maturation divisions. is produced in the ovary during female gametogenesis.
The Formation of Oocyte or Oocytogenesis is a part of Oogenesis. In mammals it starts in the germinal epithilium. 


The first cryopreservation of sperm was in 1953. Dr Christopher Chen from Australia reported the world’s first pregnancy using previously frozen oocytes in 1986.

Oocytes rarely survived the freeze/thaw aspects of the egg freezing process well primarily since the egg is the largest cell in the body and is mainly comprised of water. Orignially, the water content iniside the cell formed ice crystals that destroed the egg during the traditional egg freezing process.A number of advances in our knowledge of oocyte preservation, oocyte physiology and laboratory techniques are helping us make this a reality.This discovery was a breakthrough in the human reproductive sciences. This technology has helped women all over the world to conceive children but some of them it helped in specific are as follows:
1.Young women who are facing chemotherapy or irradiation for treatment of fatal diseases to preserve their fertility. People who undergo these radiations suffer destruction of gametes. Therefore, the opportunity to preserve this chance to have children later in life is crucial.
2. Women who are busy with their careers and decide to postpone motherhood; because of this technology can conceive children in older age despite diminished fertility rates. 
3.The ability to use only the limited number of eggs necessary while freezing the unused eggs will allow couples using donor's eggs to dramatically cut their expenses.
4. Some couples have ethical issues with embryo freezing as they might believe that life begins at conception, but with oocyte cryopreservation one can preserve eggs without such issues.
Oocyte Conservation Techniques
The main difference between sperm freezing and oozyte cryopreservation is that 
 the change in cryoprotectants used to protect the egg during the egg freezing process.Cryoprotectant acts as an “anti-freeze” to protect the delicate eggs as the temperature drops, thus stopping it from freezing. The embryos are easier to thaw/freeze because their membranes tolerate stresses as for the sperms they are 1/80th the size of an egg.

The greatest success has been achieved with protocols that use slow egg freezing/rapid thaw protocols.Common cyroprotectants include an alcohol (1,2-propranediol), a carbohydrate (sucrose) and a solvent (DMSO). Researches show that increase in the concentration of sucrose results in comparatively safer and improved survival rates, survival and pregnancy rates. If oocytes are placed directly in a medium without cryoprotectant after thawing, they can swell and burst due to diffusion.

The use of nonpermiating molecules like sucrose act against the flow of water in cells. People have recently undertaken investigations using a process called vitrification; a process that utilizes ultra rapid egg freezing techniques.This technique is susceptible to human errors thus exposing eggs to damaging levels of cyroprotectant and direct exposure of liquid nitrogen which can cause infection.

Risks and Issues:

1. The cryopreservation process is risky and the mature oocyte can be easily damaged. Intracellular ice may damage plasma membrane and change the membrane bound enzymes and membranes.
2. Microtubules are temperature sensitive and depresisons can occur at 0 degree celcius. This is damamge to the meiotic spindle that may cause nondisjunction.
3.Cytoplasmic organelles such as mitochondria are susceptible to damage.
4.Additionally, oocyte DNA appears to be destroyed via apoptosis during cryopreservation and subsequent culture , which may also play a role in the overall poor recovery of normal oocytes and embryos.
4. Parents might have ethical issues with this procedure because of it's unnatural nature.

Ethical Issues

1.Some people might believe that a woman is exploited through egg harvesting.
2. Cryopreservation is morally problematic for many from a Christian worldview such eggs are intended for use outside of the marital relationship or as a means of treating infertility within a marraige which would introduce a third party.


I think this process can further be enhanced if there is a substitute for nitrogen so that there is no infection caused when there is a leak; also if there is a container that can keep the temperature stable for longer than 24 hours if there is a power loss so that the cell membrane does not collapse.

Help:

http://en.wikipedia.org/wiki/Oocyte#Formation

http://www.ivf-indiana.com/education/egg-freezing-risks-benefits.html
http://www.nyufertilitycenter.org/egg_freezing/cryopreservation_process
http://www.extendfertility.com/oocyte-cryopreservation.htm

http://www.rbmojournal.com/search/quick?search_area=journal&search_text1=cryopreservation&restrictName.rbmo=rbmo
http://en.wikipedia.org/wiki/Oocyte_cryopreservation#Success_rates
https://www.thieme-connect.com/ejournals/abstract/10.1055/s-2002-23515
http://cbhd.org/content/egg-cryopreservation-update-emerging-reproductive-technology