Embryo Freezing Process

Embryo freezing or cryopreservation of embryos is the process of preserving the embryos at sub-zero temperature at stages of development selected by doctor corresponding to pre-implantation. Embryo freezing is a procedure that allows couples or people to store embryos for future use.

What is Embryo?

Embryo is formed in IVF procedure after taking out oocyte (ovum) from female partner’s ovary and taking sperms of male partner and doing their fertilization process in lab maintaining the culture conditions.

What is pre-implantation?

Pre-implantation means that normally in uterus embryos get implanted at blast cyst stage. So, before that stage is reached at day-5 of doing fertilization, embryos are frozen.

Indications of embryo freezing:

  • during IVF process, extra embryo left after transferring in uterus of couple.
  • if doctor aborts the procedure of doing embryo transfer in that particular cycle because of any reason.
  • if couple wants to get embryo transfer done later because of personal issues.
  • if extra embryos are left formed from donor oocyte and donor semen sample.

Process of freezing and storing embryos:

Selection of embryos:

  • Only good quality embryos of grade -1 should be frozen.
  • Blastomeres (cells) of embryos should be equal size and spaced equally.
  • No minimal fragmentation in embryos.
  • Freezing low quality embryos is of no use in future for patients.



Embryos can be frozen at different stages of their development-when they are at two to eight cell stages or later in their development called the blastocyst stage. Embryologists monitor the development of the embryos over next three to five days, after which discussing with clinical doctor, suitable embryo for implantation. Out of which extra left after transfer are taken for embryo freezing.

The process used for preserving or freezing is called cryopreservation. It involves replacing the water in the cells of embryo with the substance called cryo protectant (which is like antifreeze for cells).embryologists then leaves the embryos to incubate in a machine called incubator in increasing levels of cryo protectant, embryologists cools the embryo to its preservation state for which any of the two freezing methods used, which are as follows:

  • Slow freezing: – in this method embryos are placed in sealed tubes, then slowly lowering the temperature of tubes. It is cooled at rate of 0.3 degree Celsius/minute until they are stored in liquid nitrogen at -196 degree Celsius until the time of thawing.
  • Vitrification:-it is a rapid freezing technique that was higher strength of cryo preservation and water molecule don’t have time to form ice-crystals, instead solidify into glass like structure. In this freezing rate is approx 15000 degree Celsius/minute.


Which is better?

It should be remembered that speed is really important for success of embryo freezing. longer the time taken for freezing , more likely ice  crystals form in the cell which are detrimental for cells while thawing the embryos .in vitrification crystals does not form in cells , embryos quickly solidified.

Studies found that vitrified embryos have 83% thaw survival rate compared to slow freezing of 65% survival rate.

How long embryos can be frozen?

Embryos can remain on ice for years. to date, the longest frozen embryo to give live birth was on ice for13 years, when thawed and transferred to uterus but important is freezing conditions should be favorable and consisteny.embryo should be carefully sealed inside a tank of liquid nitrogen and monitored to keep it at least 31 degrees (-196 degree) Fahrenheit below zero.

Do frozen embryos deteriorate?

They are held in suspended state in liquid nitrogen, so they do not deteriorate. But with slow freezing method sometimes cells are damaged while thawing, survival rate of frozen embryos while thawing:


Can embryos be frozen twice:

 Multicell cell embryos once had 76.3% survival rate after thaw and second time frozen had 74% survival rate .so, they can be frozen again.

Why frozen embryos increases chances off successful pregnancy?

It cannot be clearly stated that frozen embryo cycles have more chances of pregnancy then fresh IVF cycles, but certain studies and experienced documents it to have a better outcome of following reasons:

  • Frozen embryos provide patient with additional cycle with less cost.
  • More concentration of doctor is on preparation of uterus and not on stimulation of ovaries.
  • No risk of hyper stimulation and elevated estradiologestreone hormone is there-giving better implantation rates.
  • Pregnancy can be planned with free and positive mind giving better success.


Risks of freezing embryos

Embryos freezing are very safe and often have successful pregnancy and delivering provided the conditions and techniques used are best. There is no proof that babies with frozen embryos have more congenital defects. No such risk is indicated.


Embryo freezing cost

The cost of embryo freezing is basically for freezing and thaw media used and for maintenance of embryos in liquid nitrogen. Then cost is between 30000 INR to 70000 INR/YEAR. At our centre, we charge 30000 INR/YEAR.


Why our clinic?

  1. Verification method is used for freezing embryo, which is less harmful for embryos.
  2. Only good quality grade -1 embryos are vitrified.
  3. Success rate of thawed embryos is more that 85%.since last 12 years.consistant success rates.
  4. Implantation success rate is more than 90%.
  5. Pregnancy live birth rate is more than 75%.
  6. Our doctors are very particular about giving pregnancy to patient with honest and best of ability.



  • Embryo freezing provides additions cycle patient and advantage of planning pregnancy.
  • Vitrification is better process of freezing with good success rate
  • Embryos can be frozen for many years and give good live birth rates.
  • Maintenance of temperature of tanks is must for embryos.
  • No risks involved with frozen embryos.
  • Frozen embryos have little better outcome then fresh cycle become of various factors.
  • Our clinic has excellent success rates with frozen embryos.