FOT (Frozen Oocyte Thaw)

    Last updated date: 30-Jan-2023

    Originally Written in English

    FOT (Frozen Oocyte Thaw)

    FOT (Frozen Oocyte Thaw)


    Egg freezing, also known as mature oocyte cryopreservation, is a technique used to preserve a woman's future fertility.

    Unfertilized eggs retrieved from your ovaries are frozen and kept for later use. A frozen egg can be thawed in a lab, mixed with sperm, and put in your uterus (in vitro fertilization).

    Based on your requirements and reproductive history, your doctor can help you understand how egg freezing works, the possible hazards, and if this technique of fertility preservation is suitable for you.


    Why It's Done?

    Doctors care

    If you are not ready to become pregnant right now but want to ensure that you can get pregnant later, egg freezing may be an alternative.

    Egg freezing, unlike fertilized egg freezing (embryo cryopreservation), does not require sperm since the eggs are not fertilized before they are frozen. However, just as with embryo freezing, you'll need to utilize fertility medicines to induce ovulation and generate several eggs for retrieval.

    You might consider egg freezing  &thawing if:

    • You have a condition or circumstance that may have an impact on your fertility. These might include sickle cell anemia, autoimmune disorders like lupus, and gender variation, such as transgender identity.
    • You require therapy for cancer or another condition that may impair your ability to conceive. Certain medical treatments, such as radiation or chemotherapy, might have a negative impact on your fertility. You may be able to have biological children later if you freeze your eggs before treatment.
    • You are having in vitro fertilization. For religious or ethical reasons, some people choose egg freezing to embryo freezing when undergoing in vitro fertilization.
    • You wish to preserve younger eggs now for future use. Freezing eggs at a younger age might help you get pregnant when you're ready.

    You can use your frozen eggs to try to conceive a child with sperm from a partner or a sperm donor. A donor can be known or anonymous. The embryo can also be implanted in the uterus of another person to carry the pregnancy.


    Risks of Oocyte Freezing & Thawing

    Risks of Oocyte Freezing & Thawing

    Egg freezing/thawing carries various risks, including:

    • Conditions related to the use of fertility drugs. In rare cases, using injectable fertility drugs to stimulate ovulation, such as synthetic follicle-stimulating hormone or luteinizing hormone, might cause your ovaries to become enlarged and painful immediately after ovulation or egg retrieval (ovarian hyperstimulation syndrome). Abdominal discomfort, bloating, nausea, vomiting, and diarrhea are all signs and symptoms. Even more unusual is the chance of acquiring a more severe version of the condition, which can be fatal.
    • Egg retrieval procedure complications. Rarely, use of an aspirating needle to retrieve eggs causes bleeding, infection or damage to the bowel, bladder or a blood vessel.
    • Emotional risks. Egg freezing can provide hope for a future pregnancy, but there's no guarantee of success.

    If you use frozen eggs to have a baby, the chance of miscarriage is mostly determined by your age when the eggs were frozen. Miscarriage rates are greater in older women, owing to their older eggs.

    To present, no research has found an increase in the incidence of birth abnormalities in babies born as a consequence of egg freezing. However, additional study on the safety of egg freezing is required.


    How You Prepare?

    Freezing your eggs

    If you're thinking about freezing your eggs, seek for a reproductive clinic that specializes in the procedure. Experts are often referred to as reproductive endocrinologists.

    The Centers for Disease Control and Prevention and the Society for Assisted Reproductive Technology both publish online information regarding pregnancy and live birth rates at U.S. reproductive clinics, while data on pregnancies utilizing frozen eggs is limited. However, keep in mind that the success rate of a clinic is determined by a variety of factors, including the ages of the women it serves.

    If the cost of egg freezing concerns you, inquire about the prices involved with each phase of the operation as well as the yearly storage fees.

    Before beginning the egg-freezing process, you'll likely have some screening blood tests, including:

    • Ovarian reserve testing. On day three of your menstrual cycle, your doctor may test the levels of follicle-stimulating hormone and estradiol in your blood to evaluate the amount and quality of your eggs. The results can help anticipate how your ovaries will react to fertility drugs.

    To acquire a complete picture of ovarian function, another blood test and an ultrasound of the ovaries may be done.

    • Infectious disease screening. You'll be screened for certain infectious diseases, such as HIV and hepatitis B and C.


    What You Can Expect During Oocyte Freezing & Thawing?

    Oocyte Freezing & Thawing

    Egg freezing has multiple steps — ovarian stimulation, egg retrieval freezing &thawing.


    Ovarian stimulation

    You'll take synthetic hormones to stimulate your ovaries to produce many eggs rather than the one egg that matures monthly. Among the medications that may be required are:

    • Medications for ovarian stimulation. You might inject medication such as follitropin alfa or beta (Follistim AQ, Gonal-f) or menotropins (Menopur).
    • Medications to prevent premature ovulation. Your doctor might prescribe an injectable gonadotropin-releasing hormone agonist such as leuproline acetate (Lupron Depot) or a gonadotropin-releasing hormone antagonist such as cetrorelix (Cetrotide).

    Your doctor will keep an eye on you during therapy. Blood tests will be performed to assess your response to ovarian-stimulating medicines. Estrogen levels rise as follicles form, whereas progesterone levels stay low until after ovulation.

    Vaginal ultrasound – a treatment that utilizes sound waves to generate an image of the interior of your ovaries — will also be performed at follow-up appointments to monitor the development of fluid-filled sacs where eggs mature (follicles).

    When the follicles are developed enough for egg retrieval, which usually occurs after 10 to 14 days, an injection of human chorionic gonadotropin (Pregnyl, Ovidrel) or another drug can assist the eggs mature.


    Oocyte retrieval

    Egg retrieval is usually done under anesthesia at your doctor's office or a facility. Transvaginal ultrasound aspiration is a typical procedure in which an ultrasound probe is placed into your vagina to detect the follicles.

    A needle is then inserted into a follicle via the vagina. The egg is extracted from the follicle using a suction device attached to the needle. Multiple eggs can be extracted, and studies suggest that the more eggs extracted — up to 15 each cycle — the greater the odds of conception.

    You may have cramping after egg retrieval. Because your ovaries are still swollen, you may experience fullness or pressure for several weeks.



    Your unfertilized eggs are frozen to subzero temperatures shortly after they are extracted to preserve them for future use. The composition of an unfertilized egg makes it more difficult to freeze and lead to a successful pregnancy than the composition of a fertilized egg (embryo).

    The most popular method for freezing eggs is known as vitrification. With fast chilling, high quantities of chemicals that aid in the formation of ice crystals during the freezing process (cryoprotectants) are utilized.



    Step 1. Locate Your Eggs.

    It's time to find your eggs and figure out how to get them to your fertility clinic. They might be in your fertility clinic's storage, or if you froze your eggs five or six years ago, they could be in long-term storage. In any case, make sure you notify the clinic or your fertility doctor of your plans. Check to determine whether a media kit, which is the fluid used by the lab to thaw your eggs, is required. A competent lab will handle this stage for you, but it's important to watch out for yourself since your eggs are valuable and you only have one chance to thaw them.

    Make sure to seek out the safest situation possible and make sure that the lab you’re working with understands the protocol of how your eggs were frozen because that determines how they get thawed.

    Step 2: Decide if you want to unfreeze all your eggs.

    Suppose you have 20 frozen eggs. Perhaps you thaw five and leave the others frozen to see what happens. Having unused embryos means various things to different individuals, so think about it carefully. If your relationship isn't as secure as you'd like it to be, you might not want to fertilize all of your eggs with your partner's sperm and reserve some eggs for later, just in case.

    Step 3. Complete Your Preconception Testing.

    It’s a new first step for every fertility patient, even if you’ve already frozen your eggs, which will ensure you are taking the right path and have the highest likelihood for a healthy pregnancy and baby.

    Step 4: Complete Your Infectious Disease Labs.

    Even if you are confident that you do not have any sexually transmitted diseases, these tests are required before to your transfer. The tests you receive will be determined by your state, however most states need these labs to be performed within two years after your embryo transfer to ensure that you are not carrying any diseases that might harm your baby's growth. Most reproductive clinics will arrange for a blood draw through a nearby lab or a lab of your choosing.

    Step 5: Implantation Testing.

    Everyone should get implantation testing before transferring. It isn't only something patients do after an unsuccessful transfer. It's something you do ahead of time to increase your chances of getting pregnant with these eggs. The ERA test informs you exactly when your uterine lining is ready for the transfer by informing me how many hours of progesterone you need to be on before the transfer.

    It's the uterine version of an Evite that gives you the precise arrival time for the "embryo party." If your embryo arrives too early or too late, it will not remain and implant. Your embryo has nowhere to sit if your uterine lining isn't ready. If the lining is post-receptive, the embryo will not be able to settle in comfortably. It's essentially a simulated IVF cycle in which you take medications as if you're going to transfer but then don't. Instead, we do an endometrial biopsy to examine the lining of your uterus.

    Step 6: Make Embryos.

    It's time to start making embryos when your eggs have thawed. The embryologist is in charge of this procedure. Some eggs are fertilized by dropping sperm on them. This occurs when you use fresh sperm from your partner or unfrozen donor sperm. Some are injected with sperm by an ICSI procedure in which the embryologist manually picks one sperm to insert into the egg. Fertilization begins instantly, even though we won't be able to see it for another 18 hours.

    Step 7: Decide Whether You Want to Transfer Fresh or Frozen Embryos.

    When you're ready to implant your embryos, you put yourself on hormones for a few weeks. Initially, estrogen overlapping with progesterone. You can transfer an embryo without first freezing it, or you can freeze it and then prepare your body for the transfer. The answer is dependent on the number of eggs you have and how old you were when you froze them. 

    The information provided by the egg freeze report is invaluable. When I perform an egg freeze for a patient, doctors always inform them of their thoughts on egg viability. You want to know this because if you thawed the eggs and discovered that they didn't look as good as they did when they were frozen, you could be disappointed that you didn't have the opportunity to conduct another egg freeze. So consider the following: 

    • How many children do I want? 
    • Do I have enough embryos to start a family? 
    • Even if you're utilizing frozen eggs, there's still the possibility of another IVF round or egg freeze if necessary.


    Do You Want to Do Genetic Testing on Your Embryos?

    Testing on Your Embryos

    It’s important to know that this test is just about chromosomes and it can’t predict many genetic diseases, so that’s why it’s also essential to do carrier screening to see if you and your partner or donor sperm have shared genetic mutations.

    Some people think that when you say genetic testing, it means you can learn everything about your embryo. We’re not there yet. Doctors can’t tell your child’s height, their eye color or their IQ. All they can know is whether the chromosomes are balanced in a way that you’ll have a higher chance of pregnancy and a lower chance of miscarriage. And even a genetically tested embryo has a 75 % chance of implanting because nothing is guaranteed. When it comes to human biology and thawing your eggs there is no such thing as a 100% guarantee.


    How Long Does Oocyte Thawing Take?

    Pregnant Woman

    The embryo devitrification process is a relatively quick one. It takes around 15 minutes. However, it should be taken into account that some of the tools required to perform the procedure need to be at 37ºC and so prior preparation is necessary.


    Do All Embryos Survive the Freezing & Thawing Process? 

    Freezing & Thawing Process

    We expect the majority of embryos to survive, however some do not survive. The survival rates for good quality blastocysts are approximately 90-95%. Blastocyst survival rates are known to be poorer when the blastocyst grade is borderline or poor quality.

     It is important to understand that as well as survival, blastocysts need to show ‘signs of life’ to be suitable for embryo transfer. ‘Signs of life’ are recorded by a Clinical Embryologist when the embryo starts to re-expand. Blastocysts can often contract into a tight ball of cells during the freezing/warming process and need time to re-expand. Re-expansion can take between 1-2 hours to observe, this may delay your embryo thaw results on the day of your embryo transfer. If your embryo does not survive the thawing process and you have another embryo in storage, we will ask your permission to take the second embryo out of storage for thawing.


    Does Thawing Process Alter Embryo Survival Rate?

    Although the two procedures stated above exist, the excellent results obtained with vitrification/devitrification have made it the technique of choice in IVF laboratories. The survival rate is around 100%.

    The likelihood of obtaining a pregnancy, on the other hand, is less dependent on the cryopreservation process and more dependent on the quality of the embryos and the state of the endometrium. However, increased survival rates after devitrification assure a better long-term prognosis since it increases the number of accessible embryos.


    Can You Re-freeze Embryos? 

    Yes. Doctors can re-freeze embryos if needed. As far as we can tell, if the embryo has survived the freezing and thawing process, it can be re-frozen. The chances of the embryo not surviving the second thawing process may be slightly increased.



    Many women are wondering whether or not to preserve their eggs for the future. But doctors rarely look to the future: what happens when it's time to thaw them and have a baby?

    Too many women in their late thirties and forties came into clinic, struggling with fertility and wishing they had known more about it when they were younger. They would have done it if someone had told them to get their fertility levels evaluated and to think about egg freezing. The older we get, the more the quality and quantity of our eggs decrease, and this begins most dramatically after the age of 35.