Fertility Treatments


Vitrification, also known as flash freezing, is a new cryopreservation technique that gives embryos a better chance of survival than slow freezing.


During in vitro fertilisation, a patient will produce more than one or two usable embryos. But the doctor doesn’t use all of these eggs for implantation during the first attempt out of the fear of issues like multiple pregnancies. Instead, the embryos that aren’t used for implantation are frozen to be thawed and used later. Similarly, the patient may also go for egg freezing instead of embryos to keep better control over the process. 

Going ahead with freezing would mean that if your current IVF attempt fails for some reason, you won’t have to go through the discomforts of egg and sperm collection. For example, their uterus may not be prepared for implantation for some women, making it inhabitable for the embryos. But embryo freezing helps the doctor get the cycle back in sync to implant the embryos when it’s the right time. Another benefit of freezing the embryos is the chance provided to the patient to try again in the future if they want another child or their previous attempt was not successful. Finally, since freezing the eggs can help you preserve the age of your embryos, you will have a better chance of pregnancy with frozen embryos than fresh embryos in your older age. 

Currently, there are two ways in which an egg can be frozen: slow freezing and fast or flash freezing (vitrification). First, your sperm, eggs or embryos will be mixed with an antifreeze solution to ensure that the freezing process goes smoothly. Then the solution will be frozen slowly or quickly through liquid nitrogen. Finally, the embryos will be thawed (gently warmed) as per the requirement.

Until recently, your embryos would have been frozen with the help of a process called “slow freezing”, which had certain issues. But thanks to the latest technology, doctors nowadays use flash freezing or vitrification to ensure the embryos are frozen successfully and improve the embryo cryopreservation.

Understanding Vitrification

One of the latest cryopreservation techniques is flash-freezing or vitrification, which provides a better chance of survival for the embryos than the slow-freezing technique, and alleviates most of the drawbacks exhibited by the slow-freezing technique. 

During the flash-freezing, your embryos will be mixed with an antifreeze liquid, and the temperature will be brought down instantly to ensure that the solution is frozen in just a few moments. The antifreeze liquid ensures there is no formation of crystals and no damage from them. 

But there is a catch. Vitrification is a more complicated process that requires extensive training and experience on the doctor’s part. So choosing the doctor wisely is the key. In addition, the movement of embryos in this process by the doctor will be manual, making it prone to critical disturbances and variability of the results. 

Vitrification is a cryopreservation process that freezes the embryo solution quite rapidly to form into ice instantly. It ensures that the water molecules in the solution don’t develop any icy crystals that may harm the embryos. As mentioned earlier, vitrification is considered a more complicated method than the slow-freezing approach, but it provides almost the same pregnancy rates as IVF with fresh embryos. 

Slow freezing is considered less advantageous than vitrification as ice crystals may form during the former, which may damage the embryos upon breaking during the thawing process. But when it comes to flash-freezing, the embryos will be frozen instantaneously, ensuring little to no formation of ice crystals.

Several pieces of research have shown quite minimal damage to the specimen as a result of flash-freezing. Also, this process helps preserve the embryos for an indefinite time.

How Successful Is Vitrification?

How can frozen be better than fresh? In reality, several studies have shown that IVF performed with frozen eggs or embryos is more successful than IVF with fresh eggs and embryos. The success could be attributed to the ovulation stimulation medications. 

The hormonal stimulating supplements you take for increasing egg production may still be in your system during the fresh embryo transfer in IVF. But when it comes to vitrification, your body will have time for your hormones to return to normal levels. That’s probably why the experts consider vitrification as more successful than fresh embryo transfer. 

Although vitrification is considered extremely successful, there is no guarantee of every embryo surviving the freezing and thawing process. Also, even after surviving, they may not be able to fertilise or transfer to the uterus. But vitrification can still help you improve the success of IVF pregnancies.

How Does Vitrification Work?

Vitrification is a cryopreservation process for transforming the liquid inside embryos, sperm and eggs to a glass state. Earlier, the slow-freezing method was used to freeze the embryos quite slowly, leading to them forming ice crystals, which could have damaged the embryos during thawing. But since the vitrification freezes the embryos almost instantaneously, there won’t be a chance for any ice crystals to form. 

Here are a few steps followed by the experts during embryo cryopreservation through vitrification:

  • First off, the embryologist will place your sperm, eggs or embryos in a low concentration bath with cryoprotectants (antifreeze liquid). The sucrose in this solution may extract the water out of the embryos, sperm and eggs. 
  • After that, they will place these reproductive materials in a high concentration bath of this solution for less than 60 seconds, freezing the materials instantaneously. That will prevent the formation of ice crystals. 


After vitrification, these reproductive materials will be able to last indefinitely, so you may conceive another child when you want or want to try again in case of a failed IVF attempt. In addition, with the help of the latest artificial reproductive techniques like IVF, you’ll be able to use the cryopreserved embryos for pregnancy after thawing.


Suppose you are a woman who has already gone through the egg retrieval process and successfully fertilised with the sperm. So what’s next for you? 

You can go for a process called embryo cryopreservation. There are two ways to do it: slow-freezing and flash-freezing (fast-freezing or vitrification). Before they are frozen through either method, your embryos, sperm, or eggs will be mixed with an antifreeze liquid. Then, they will be frozen either slowly or by vitrification through liquid nitrogen. Finally, when they are ready to be used for implantation, the embryos will be thawed (gently warmed). 

In the slow-freezing process, the temperature of embryos, sperm or eggs will be brought down a few C at a time until it reaches about -320 degrees celsius. This freezes them quite slowly. 

But when it comes to flash-freezing or vitrification, the embryos, sperm, and eggs will be frozen instantaneously to a temperature of around -196 degrees celsius. So when compared to slow freezing, which takes a few hours, vitrification just takes around a few minutes. 

As mentioned before, IVF with frozen embryo transfer is considered to be more successful than fresh embryo transfer. If you have any other queries regarding vitrification or flash-freezing, please consult the Fertility experts at Siya Health, or call our Siya Fertility Counsellor today.

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