How is the process of Embryo or Oocyte Freezing done?


During the process of Vitrification, liquid is super­cooled to a temperature at which the viscosity is so high that the liquid achieves amorphous glassy solid state, having no ice crystals. Since there is no formation of ice crystals, there is no cryo damage to cells during the process of Vitrification.

The sudden cooling of embryos or oocytes are being achieved by dipping them in Liquid Nitrogen which has a temperature of -196 degrees.

They say that a picture is worth a thousand words. And these days a video is worth a Million! Here is a small video showing the exact process of Embryo Cryopreservation in IVF Labs:

Is Embryo Freezing Safe?

The technique of vitrification has revolutionized the cryopreservation of gametes (oocytes) as well as Embryos. Technically it is possible to achieve 100% cryosurvival of gametes using Vitrification. It has been possible to achieve more than 70% success rate in Frozen Embryo Transfers due to better media and protocol.

Data from all around the world shows that most clinic’s prefer a Freeze All IVF Cycle as compared to traditional IVF Emrbyo Transfer and upto 70% of Embryo Transfers are FETs. This technique would not have been popular if it were not successful. There is a huge debate about many aspects of IVF and it’s safety, however there has not been any concrete evidence to prove otherwise.

What is the difference between fresh Embryo Transfer and Freeze All Protocol? Which is better?

Fresh Embryo Transfers are done in the same cycle when the patient undergoes Ovum Pickup or egg retrieval. The Embryo transfers are planned on Day 3 to Day5.

During a Freeze All Protocol, embryos are formed and cryopreserved in the cycle when OPU is done. These cryopreserved embryos are warmed in subsequent cycle, typically after 1.5 months when the endometrium is ready.

The main benefit of FET or Frozen Embryo Transfer over a Fresh IVF Embryo Transfer is that the endometrium is more receptive in FET cycles as compared to the cycle during which ovaries are stimulated to produce multiple eggs. The receptivity of the endometrium is much higher during a natural cycle, leading to a significant rise in implantation rates of the embryo.

However, in many cases Fresh Embryo Transfers are equally successful. To know more please visit our blog:

Should I freeze Embryo or Eggs / Oocytes ?

Technically, freezing and warming give better result for Embryos (Day 3 or Blastocyst) as compared to oocytes. Hence for married couples, or couples with constant partner, freezing Embryo’s make more sense. Oocyte freezing should be considered for cases of Fertility Preservation of unmarried women.

How long can you store embryos or oocytes by freezing?

Technically, once the embryos are cryopreserved, they can be stored indefinitely under Liquid Nitrogen Tanks. There has been reports on birth of healthy baby after a couple decided to adopt and embryo that was frozen almost 30 years back.

Once dipped in Liquid Nitrogen, Embryos, Oocytes and sperms can stay in the state of suspended animation indefinitely. Each country has different regulation to maximum number of years upto which gametes can be stored. In India, the ICMR guideline limits the maximum number of years for storage of gametes to 5 years.

Is the procedure of Embryo Transfer different for Frozen Embryo Transfers?

No, the process of Embryo transfer is exactly the same whether the Embryo is Fresh or Warmed.

The content of the blog came out of an Interview with Dr. Gajendra Tomar (leading Infertility & IVF Specialist from Indore Infertility Clinic) while discussing various aspects of IVF Cycle.