What is Vitrification of Eggs and how is it done?

May 2, 2024
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Egg preservation, also known as oocyte cryopreservation is one of the best ways of fertility preservation in women. Egg preservation is an assisted reproductive technology (ART) method that enables a woman to save the ability to get pregnant in the future. The frozen egg can be stored for many years and can be thawed and used for pregnancy when required, making it a very desirable fertility preservation option for many women.

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Why is egg freezing done?

Age is one of the most important factors that affect female fertility and hence egg freezing is preferred by women who are not yet ready to get pregnant but wish to get pregnant in the future. Social egg freezing is preferred by women who are getting older without a partner or who wish to get married later due to some other commitments. Egg freezing is also an option if a woman is affected by certain conditions or illnesses that may affect fertility.

Types of egg freezing procedures:

Depending on the pace of freezing, there are two main types of freezing the egg:

  • Slow freezing: in this process, the embryo or the egg is cooled down slowly in a controlled fashion and is stored in liquid nitrogen for further use.
  • Vitrification: it is relatively a newer technique of egg or embryo freezing. Contrary to slow freezing, in vitrification, the eggs are cooled very rapidly. Thus, it minimizes the risk of crystal formation in the cells.



As already mentioned, vitrification uses flash cooling the oocytes by directly immersing it into liquid nitrogen. The desired temperature to be attained is -196ºC as at this temperature all the biological activity practically stops. By immersing the cell directly into liquid nitrogen, this temperature is instantly attained as compared to slow freezing which may take much more time.

The process:

The process of vitrification is as follows:

  • Ovarian stimulation: it is the first important step for the vitrification process. Hormones are administered to produce multiple eggs at one time as compared to a single egg.  
  • Egg collection: when the follicles are ready, the eggs are collected. This usually happens after 10 to 14 days of ovary stimulation and is done under sedation. One of the most common methods of egg collection is transvaginal ultrasound aspiration in which ultrasound is used to identify follicles and then a needle is used to retrieve the eggs.


  • The eggs are then dipped into cryoprotectants, which remove the water from the cell to prevent ice formation during freezing. Ice-formation may even lead to cell rupture and hence must be prevented for successful freezing.
  • Eggs are then cooled rapidly and stored in liquid nitrogen at a temperature of -196ºC.

The eggs can be kept frozen in this way for many years. When pregnancy is desired, the eggs are thawed and used as required.

Advantages of vitrification over slow freezing:

The most important advantage of vitrification over slow freezing is that it significantly lowers the risk of crystal formation. Crystal formation is the single biggest threat to the egg freezing process as it may rupture the cell membrane. Many studies show that the success rates of vitrification (defined by the percentage of eggs that survive the thawing process) is significantly higher than slow freezing, making it the more preferable option for egg freezing. Cloudnine is one of the best pregnancy and maternity care hospitals in India. Cloudnine provides you with a wide range of services and facilities including oocyte cryopreservation. Our experts are highly qualified and experienced in performing procedures like vitrification for egg preservation. We also provide you with world-class egg preservation facilities, enabling you to preserve your eggs as long as required.