Fertility Treatments

Embryo freezing

Embryo freezing, also known as cryopreservation, is a technique used by fertility doctors to store any extra embryos produced during IVF.


It’s quite sad when a couple has been trying to have a baby forever but can’t. It may result in quite a disappointment after a while. But thanks to the latest technological advancements, you can be a parent with Vitro fertilisation or IVF. 

In layman terms, in IVF, the male partner’s sperm and female partner’s eggs are kept in a dish together in a special fluid at a fertility lab. When the sperm and egg are fertilised to form a new cell, it will result in an embryo. After this process is completed, the newly formed embryo will be placed in the woman’s uterus for implantation. If the embryo latches onto the uterine wall properly, it will develop into a pregnancy. 

During the procedure for IVF, the female partner will be prescribed medications for ovarian stimulation. It means that these medications will help their ovaries produce more eggs than they usually would. As a result of medications, the male partner will also produce a high number of sperm cells. With the number of sperm cells and egg cells being high, multiple embryos will be formed after fertilisation. 

Then, based on the woman’s age and a few other factors, the doctor will place 1 to 2 3 embryos in her uterus for implantation. But, of course, not all embryos will be placed inside the uterus. Otherwise, there will be a chance of multiple births. So the embryos left will be processed cryopreserved [embryo freezing].

What Is Embryo Freezing?

Embryo freezing, or cryopreservation, is a process used by fertility doctors to freeze the unused or extra embryos produced or fertilised during IVF, or any other artificial reproductive techniques, including ICSI (intracytoplasmic sperm injection). The simplest and initial step of embryo cryopreservation is freezing.

After freezing them, the embryos are stored in a facility and used as per the requirement in the future. That will help you as a fertility treatment patient save money and time on future IVF cycles if any previous attempt fails. That’s because the female and male partners won’t have to go through egg and sperm retrieval and spend more money on ovarian stimulation medications. 

Embryo preservation is considered an elective procedure, and people opt for it to keep their options open to becoming a parent in the future. However, several other reasons may tempt people to go for cryopreservation, including increasing age, treatment for cancer or another mortal illness, risk of illness and injury, etc. 

You should consider a thorough consultation with your fertility specialist or come over to Siya Health if you are looking to better understand embryo freezing or cryopreservation.

How Are Embryos Frozen And Stored?

The specialists who usually process the cryopreservation of embryos are the reproductive endocrinologists. They use two processes for it: slow programmable freezing and flash freezing or vitrification. These processes differ in more aspects than one. But they both work by cooling the fertilised embryos with some cryoprotectants or antifreeze fluids. Embryonic and other cells are mainly made from water, so there is a concern of ice formation, which may inflict damage to the cells during the thawing process. That’s why the specialists use cryoprotectants to protect the embryonic cells from damage during crystallisation and thawing done during the cryopreservation. 

Slow programmable freezing is a process in which the doctor, as the name suggests, freezes the embryos slowly in stages in a special machine. Then the cryoprotectants are added. Once the embryos are frozen, they will be transferred into -321 degrees Fahrenheit liquid nitrogen for storage. The whole process takes roughly around 2 hours. 

Vitrification or flash freezing is a newer and more successful process. The doctor places the embryos in a solution containing cryoprotectants in a much higher concentration in this process. After that, the container will be plunged into liquid nitrogen, turning them into an ice-like formation. Vitrification freezes the embryos right before ice crystals can form. So the chances of survival of the embryos are much higher. 

All the biological activities like growth or death happening inside the embryos stop temporarily when they are frozen, and they can survive for a long time. The doctor will be able to thaw and use the frozen embryos whenever required.

Why Do Patients Choose To Freeze Their Embryos?

After completing artificial reproductive techniques like IVF and ICSI, you may be left with extra good-quality embryos. In that case, the doctor may offer you a chance to freeze them for future use instead of discarding them. That may be helpful if the current IVF attempt doesn’t work or if you want another child. 

There are several other reasons for patients choosing embryo cryopreservation:

  • The doctor may cancel your treatment mid-way after the egg retrieval or fertilisation due to an over-response from the fertility drugs. In that case, they may offer you a choice to freeze your embryos. 
  • If you are going through a gender transition, the doctor may ask you to preserve your embryo for future use before the start of reconstructive surgery or hormone therapy. In this case, cryopreservation becomes pertinent as you’ll lose your fertility either partially or wholly. 
  • If you feel like freezing is a much better option than discarding the extra embryos, you may opt for cryopreservation. 
  • You as a couple may choose to cryopreserve your embryos if you want another child in the future.  
  • If you have been diagnosed with a medical condition that may affect your fertility, you may preserve your embryos to wait for the recovery. 
  • If you want a backup in case the current IVF attempt fails, embryo freezing can be a good option.


Freezing your embryos can be elective or required, which the doctor will specify after the egg retrieval or fertilisation.

What Happens During Embryo Freezing Procedure?

After conducting a few screening tests, the doctor will perform a procedure called egg retrieval if you are ready. It is conducted as an outpatient procedure under sedation to harvest your eggs. When you are under sedation, the doctor will use ultrasound imaging to lead a catheter and hollow needle through your vaginal wall into your ovary for collecting your eggs, one at a time. The number of eggs produced by your ovaries will depend upon your body’s response to hormone medications. Then, just as a male donor’s sperm, your eggs can be frozen unfertilised. 

An embryo is created when a female’s egg cell is fertilised with a male sperm cell. Afterwards, the specialists observe the fertilised embryo grow in a petri dish for 5 to 7 days. At this stage, the doctor will test these embryos for genetic testing to ensure there is no contamination, abnormality, or congenital disability in the embryo and grade them based on their quality and probability of implantation. 

After the genetic testing, the next step will be vitrification or cryopreservation with the help of flash freezing. It replaces the water in your fertilised embryos with cryoprotectant liquid and then flash-freezes them with the help of liquid nitrogen. Cryoprotectant fluids help prevent the formation of any ice crystals that may damage your embryos.

Are There Any Risks?

Several pieces of research ensure cryopreservation does not cause any damage to the embryos, nor does it harm the baby born through it. Furthermore, contrary to popular belief, freezing the embryos for even years won’t affect their quality. 

Thanks to the latest technology, there isn’t much difference between babies born through frozen and fresh embryos. There is almost no risk involved with embryo freezing, but this process may improve the pregnancy rate. Also, several pieces of research have suggested that there is next to no risk of congenital disabilities in babies born with embryo cryopreservation.

Freezing Embryos Vs Freezing Eggs?

People often confuse freezing embryos and freezing eggs, which are quite different in the procedures. Both of these processes have their own advantages and disadvantages. So what’s the difference between the two? Will the eggs be fertilised before or after being frozen or thawed?

Whether it is freezing eggs or freezing embryos, the starting procedure will basically be the same. First, the doctor will inject hormonal medications for around 8 to 12 days to stimulate your ovaries for increased egg production. (It is important because not all of your eggs will get fertilised with sperm to form embryos. So the more eggs, the higher the possibility.)

Once your eggs are mature enough, they will be retrieved from your ovaries and frozen with the help of the flash-freezing method. These eggs will be frozen at such a low temperature that all biological activity like further development or death will be temporarily paused. The healthiness of your eggs will depend upon your age. So you may want to preserve the quality of your eggs by freezing them. 

For using them for your pregnancy in the future, your eggs will be thawed (gently warmed) and then fertilised with the male partner’s or donor’s sperm to develop into an embryo. Due to being frozen, these eggs will be of just as good quality and health as they were before being frozen. 

During embryo freezing, your eggs will be fertilised with your male partner’s or donor’s sperm with the help of IVF before being frozen. Afterwards, these embryos will be thawed and placed into your uterus. Other than these differences, the process will be the same.

What Happens If I Want To Use Frozen Embryos?

The procedure of using the frozen or cryopreserved embryos for your IVF will depend upon your situation and your medical facility. 

The doctor will check your uterine lining for thickness using ultrasound. If your uterine lining is thick enough and your progesterone levels are in normal range, you’ll be ready for embryo transfer. 

If you do not have regular periods, the doctor will prescribe fertility drugs for ovarian stimulation and medications for suppressing your natural menstrual cycle. 

When your fertility doctor feels it’s the right time, they will initiate the thawing and place the embryos in your womb.


Embryo cryopreservation is a process conducted to freeze and store your embryos to be used in the future. You may also choose to freeze your eggs before they are fertilised. 

There are almost no significant risks like congenital disabilities involved with frozen embryos. But the success rate of IVF treatments conducted with frozen embryos is considered higher than with fresh embryos. That is because embryos can be frozen for a long time, and there won’t be any side effects. But it is true; all embryos may not survive the freezing and thawing process. The doctor will explain that to you during your consultation. 

If you have any other queries regarding embryo freezing, please consult the Fertility experts at Siya Health, or call our Siya Fertility Counsellor today.

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Dr. Dipesh Sorathiya

M.S. (Obs & Gyn)
DIP. in Gynec Endoscopy (CICE)

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