• Tue. Nov 29th, 2022

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What is Freeze All in Assisted Reproductive Technology?

Assisted Reproductive Technology

Recent advancements in ART have helped increase the usage of freeze all or embryo cryopreservation practice during IVF. It is the practice to freeze developing embryos so that they can be transferred and used later giving very high pregnancy rates.

Generally during IVF, eggs are retrieved and fertilized in the laboratory to form embryos. From these, the optimum embryo is selected and then transferred to the uterus in three to five days. This is a conventional method and is called as fresh transfer. In freeze all, the embryos are not transferred right away, rather, they are frozen and stored for later use.

Why is it used:

It is primarily considered by physicians who have experience in this technique and are giving twice as high pregnancy rates in all patient groups as compared to conventional IVF. By vitrifying the embryo before the embryo transfer, they gain the option of a later transfer in a hormonally prepared endometrium which increases the implantation rates.

Additionally, many couples wish to screen the prospective embryos for genetic defects. Cryopreservation aids them in preimplantation genetic screening, through which the embryos can be tested for the set of chromosomes.

Freezing of embryos can also help to avoid going through the entire procedure of IVF again, in case the initial process does not lead to a successful pregnancy. They can also be donated to other couples or even for research.

Special care is needed to preserve the embryo cells from being harmed by ice crystals while freezing. There are two distinct methods for embryo cryopreservation, which is carried out with the help of cryoprotective agents (CPAs). These are known as slow programmable freezing and vitrification. Today Slow Freezing is considered obsolete & history.

Slow freezing method:

In this technique, CPAs are gradually added to the embryos over the period of 10 to 20 minutes, after which their temperature is slowly decreased in a machine over next two hours. These embryos are then put in liquid nitrogen at -196.1 degree celsius.


This is a faster method that utilizes stronger CPAs, which are mixed with the embryos. To prevent any damage to cells, the embryos are rapidly stored in liquid nitrogen, where they attain a glass-like state but without any formation of ice.

Can freeze all technology be done for all?

With the improvements in medical techniques for freezing and transferring of embryos, success rates of the freeze all technique have over taken the fresh transfers. Most Fertility specialists with a good lab back up will always advice vitrifying embryos and a remote Embryo Transfer to increase implantation rates for their patients..

It is also recommended to reduce the risk of OHSS (Ovarian Hyperstimulation Syndrome), which is caused due to increase in endogenous hCG. Further, freeze all is considered to prevent different conditions from negatively influencing fertility. These include polyps, adenomyosis and hydrosalpinx, among others.

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