What is embryo freezing?

An embryo freezing is the cryopreservation of embryos for future use in IVF cycles. There can be various reasons for the freezing, including – as a safety net for their ongoing IVF cycles, possible future pregnancies – should they opt for it, if one of the two individuals require to undergo a medical procedure that may limit or reduce their ability to conceive in the future. Numerous research studies have shown that there is no increase in the risk of congenital disabilities among children born from Frozen Embryo Transfer – IVF compared to normal births. Physicians can freeze and store unused embryos (fertilized eggs) created during IVF, including intracytoplasmic sperm injection (ICSI), using a process called cryopreservation of embryo freezing. Freezing the embryos is the first step of embryo cryopreservation. The frozen embryos are then stored and later thawed, as needed, for future use in IVF.

How are embryos frozen and stored?

There are two methods to freeze embryos: Vitrification (Flash Freezing) and Slow Programmable Freezing. In both these methods, the embryonic cells are cooled using various cryoprotectants (antifreeze fluids).
Given that embryos largely contain water, freezing embryos leads to ice formation and thereby damaging the cells. Thus, cryoprotectants prevent water from crystalizing during the freezing process thereby keeping the embryos from losing their integrity.

In the Slow-Freezing method, the embryologist places the embryos inside a special machine that cools the embryos in stages. Then cryoprotectants are added and once the embryos are frozen, they are stored in liquid nitrogen (-196 degree Celsius). This entire process takes about 2 hours.

In the Vitrification Method, is a newer and more successful technique. The embryologist places the embryos in a solution containing a higher concentration of cryoprotectants. The embryos are then immersed in liquid nitrogen, instantly freezing them into a glass-like substance. By doing this, the embryos are stored before ice crystals have a chance to form, thereby increasing the embryos’ ability to survive and be viable post thawing.

Irrespective of which method of freezing is used, the frozen embryos are effectively suspended in time. All the biological activities within the embryo are stooped, including cell growth or cell death. When needed, the embryos are slowly thawed and soaked in fluids to remove cryoprotectants and to restore the water within the cells. Frozen embryos can be stored for an indefinite period of time. However, the longest duration an embryo has been stored and used, resulting in a healthy pregnancy, was 19 years.

What are the risks of freezing embryos?

There are potentially no differences in babies made through frozen embryos in IVF when compared to normal born babies. The risk of potential freezing is now eliminated with the help of cryopreservation.

• Numerous research studies have shown that embryos’ freezing and thawing does not harm babies made through IVF.
  The length of time the embryo was stored also does not affect IVF success rates.
• The difference in pregnancy rates between frozen embryo transfer and fresh embryo transfer is also negligible. The stimulation process with frozen embryo transfer is gentler, with hormone levels closer to normal in the woman, improving pregnancy rates.
• Any ice crystals formed during the slow freeze process may cause damage to an embryo while thawing. This is one of the reasons vitrification is the preferred cryopreservation technique.
• Numerous research studies have shown that there is no increase in the risk of congenital disabilities among children born from frozen embryos than normal births.