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Embryo Freezing, Embryo Cryopreservation and Thawing Process

  • 4.5 (1 Votes)

Embryo freezing is a process that allows an embryo to be frozen for a specific period for future pregnancy. Enhance your understanding on processes of Slow Programmable Freezing and Vitrification along with benefits and disadvantages of embryo freezing.

Embryo freezing /embryo cryopreservation is a method of preserving viable embryo’s by cooling them to very low temperatures (-196 degree Celsius) so that they can be thawed and transferred into the uterus of a woman in future without making her undergo the process of ovary stimulation and egg retrieval all over again.

During an IVF cycle, a woman’s ovaries are stimulated to produce many eggs. After fertilization and embryo culture, the best embryos are selected for an embryo transfer. Apart from those embryos, the rest of the good ones are frozen at this point at a temperature of -196 degree Celsius, leaving them in a state of suspended animation, in which they can survive for years to come and generate successful future pregnancies.

Monitoring of Frozen Embryo’s:

Embryo freezing is carried out by carefully cooling them to very low temperatures (-196 degree Celsius) in a laboratory using specialized freezing equipment. They are then safely stored in liquid nitrogen for long periods.

There are 2 techniques of embryo freezing:

1. Slow Programmable Freezing (SPF):

In this process, embryos are slowly cooled in an anti freeze solution/ cryoprotectant, from body temperature, down to -196 degree Celsius and then stored in containers having liquids nitrogen.

In this method, damage to intracellular freezing is avoided as cooling is slow and allows sufficient water to leave the cells during freezing of extra-cellular fluid.

Freezing takes place at a rate of 1degree Celsius / minute after treatment with cryoprotectants such as glycerol or dimethyl sulphoxide. The embryos are stored within a special labeled plastic vial or straw that is sealed prior to freezing. After being frozen, they are placed inside various colored tubes called vistibules, and stored in numbered containers to avoid confusion and misidentification.


  • Slow process until the embryo finally freezes, making it a very time consuming procedure
  • Leads to formation of ice crystals inside the embryo cells thus damaging them and therefore reducing the survival rate, which in turn causes poor pregnancy rate

2. Vitrification:

This is a newer technique, which has a potential of achieving an ice-free, structurally arrested state of cryopreservation.

This process avoids intracellular and extracellular ice formation. It was, therefore, recognized as a better technique for the preservation of embryos due to less damage to the cells during cooling and warming.

Two conditions are usually required to allow vitrification, an increase in the viscosity of the medium and a depression of the freezing temperature.

When it comes to embryo cryopreservation, all stage of embryos can be frozen, i.e. Pronuclei stage (day 1 embryos), multicellular stage (Day 2, Day 3 embryos), Blastocyst Stage (Day 5, Day 6).

Vitrification has improved the potential of successfully banking the human eggs.


  • It is an ultra rapid process. It literally allows no time for intracellular ice to form. As a result, vitrification prevents trauma to the embryo.
  • Vitrified embryos have more than 95% freeze-thaw survival rate, and a pregnancy generating potential that is comparable to fresh embryos.
  • High survival rate enables us to preserve eggs safely and reliably.


  • There is always a concern about the high levels of cryoprecipitate required for the process.
  • In this process, cells are brought in direct contact with liquid nitrogen, which can act as a vehicle for disease transmission.

Storage period of embryos

Practically a frozen embryo can remain viable for an indefinite duration of time. The normal storage period for embryos is 10 years although under certain circumstances women can store their embryos for up to 55 years. The embryos are stored in sealed containers at temperatures of -321ºF. At this temperature, almost no biological processes such as aging can occur to the embryos. Storage period can be different for different parents, you need to consult your clinician whether you can do this. For those parents who have decided to store their embryos for a period lesser than 10 years, they may have to take their embryos out of storage and allow them to perish. However, for those parents who want to store the embryos for more than 50-55 years, they have to confirm that if they wish to continue storing their embryos and also if their doctor confirms their eligibility to do so. Many women have reported successful pregnancies that have resulted from eggs stored for more than twenty years. Some countries have chosen to regulate and increase the length of time an embryo can be stored. Embryo freezing or cryopreservation is expensive and time consuming, however each clinic has its own rules about what happens if a woman can no longer use her own embryos or keep them frozen.

Side effects of Embryo freezing/ Embryo cryopreservation

Almost 70% of the women have reported successful pregnancy with Embryo Freezing. Most of the side effects associated with embryo freezing mostly occur during the transferring process. The side effects are mild and moderate; some of the side effects are as follows:

  • Mild or minor side effects such as headaches, mood swings, insomnia, fluid retention, breast tenderness , cold or hot flashes etc
  • Cramping or bloating
  • Excessive bleeding
  • Feelings of fullness
  • Cancer including breasts or ovarian cancer
  • Bleeding
  • Changes in vaginal discharge
  • Infection and pregnancy complications
  • Certain birth defects, chromosomal abnormalities
  • Moderate or Overstimulation of the ovaries also known as Moderate hyper stimulation syndrome (OHSS)

Embryo Thawing:

Thawing of embryo is a process in which the frozen embryos are warmed to prepare them for transfer to a woman’s uterus.

Thawing process follows embryo freezing but only at the time of embryo transfer. The process of thawing is just the opposite of embryo freezing. Since the embryos become dehydrated at the time of freezing, they should be very carefully rehydrated while being thawed to room temperature.

In this process, the embryos are warmed up through a series of hot baths and air, along with the removal of the cryoprecipitate that are added at the time of freezing. After the warming process, the embryos are brought to normal body temperature of 98.6 degree Fahrenheit.

After all the above-mentioned processes are complete, the embryos are allowed to rest for a few hours prior to the frozen embryo transfer procedure.

The most important thing to remember is that the timing of thawing of embryo should be directly proportional to the endometrial receptivity as an optimum thickness of the uterine lining is very essential for embryo implantation.

We hope this article was helpful to you in providing useful information regarding Embryo freezing/ Embryo cryopreservation. Therefore, to have a successful frozen embryo transfer, it is important to choose a qualified and certified fertility expert. For more updates and information on embryo freezing process, you can follow Elawoman blog.

If you are looking for a specialist or a gynecologist for fertility treatments including IUI, IVF, Surrogacy and high-risk pregnancy care, you can call us at +917899912611 for proper assistance guidance.

Dr. Neha Gupta

About The Author

Infertility Specialist, IVF Specialist Dr. Neha Gupta

Dr. Neha Gupta is an Obstetrician and Gynaecologist in Gurgaon. She has been practicing for many years now. Her rich experience in Normal Vaginal Delivery, Intrauterine Insemination (IUI), In-Vitro Fertilization (IVF), Hysterectomy and Tubectomy makes her the most preferred names in Gurgaon. She has acquired MBBS in 2004, DNB from National Board of Examinations in 2009 and MS - Obstetrics and Gynaecology from Maulana Azad Medical College in 2009. She is a member of the Royal College of Obstetricians and Gynaecologists, London. Dr. Neha Gupta has an expertise in Intrauterine Insemination and is practicing at Fortis Memorial Research Institute in Gurgaon. You can get the contact details of Dr. Neha Gupta at


    1 Comment


    Kaushal Mukhi

    We recently got our embryos frozen for our future use. This technique is really useful. My wife is pregnant with IVF now and whenever we will be feeling like having our second child, we can use these frozen embryos directly.

    Oct. 30, 2018, 7:19 p.m. 4.5

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