Last updated date: 18-Aug-2023
Originally Written in English
Cryopreservation of embryos is the method of preserving an embryo at subzero temperatures, often at an embryonic stage equivalent to pre-implantation, i.e. from fertilization to the blastocyst stage.
In the 1980s, the first successful pregnancy resulted from freezing a viable embryo. Many individuals have frozen embryos and utilized them subsequently since then.
After embryo transfer, there are frequently excellent quality embryos left over after in vitro fertilization (IVF) or intracytoplasmic sperm injection (ICSI) therapy. Instead of discarding them, you can freeze them for later use (for example, if therapy does not work or if you want to try for a sibling).
Embryos can also be stored to maintain fertility so that a baby can be born at a later period.
What is Embryo Freezing (Cryopreservation)?
Embryo freezing (cryopreservation) is the process of freezing and storing fertilized eggs for later use.
Using cryopreservation, or embryo freezing, doctors can freeze and store unwanted embryos (fertilized eggs) developed through IVF, which may involve intracytoplasmic sperm injection (ICSI). The initial stage in embryo cryopreservation is freezing the embryos.
The frozen embryos are then preserved and thawed as needed for future IVF treatment. Because a woman will not need to endure multiple egg retrievals or take as many drugs, individuals presently undergoing IVF will save time and money on future rounds.
People usually choose to freeze their embryos because they wish to preserve their chances of becoming parents in the future. People frequently contemplate cryopreservation owing to factors such as cancer treatment, advancing age, or danger of damage (due to a medical condition or military deployment, for example).
Why Would You Freeze an Embryo?
Embryo freezing is frequently performed after people have undergone fertility treatments in an attempt to conceive. In vitro fertilization (IVF) and intracytoplasmic sperm injection are two examples.
These treatments fertilize eggs with sperm and can result in the formation of additional embryos. If you want to freeze excess embryos and use them later, you can do so if you:
- Postpone or cancel implantation into your uterus after an egg is already fertilized.
- Want to delay IVF to a later date.
- Want an option in case early attempts at fertility treatment fail in those with infertility or subfertility.
- Choose to donate unused embryos to other people trying to get pregnant or to researchers rather than destroy them.
Embryo freezing is also utilized to preserve fertility. A woman or person designated female at birth (DFAB) with cancer, for example, may desire to store fertilized eggs before beginning chemotherapy or radiation therapy if the treatment may interfere with their ability to conceive. Before taking hormones for the transition or undergoing gender affirmation surgery, a transgender man (transitioning to male) may also store eggs or embryos.
How The Quality is Determined?
The quality of embryos varies; those of the highest quality are more likely to implant in the womb and result in a pregnancy. If you have more than one embryo, your embryologist will utilize their knowledge and skills to choose the finest quality embryos based on factors such as:
- the number of cells present
- how fast the cells are dividing
- whether the cell division is even
- whether there are any fragments of cells present – this means that some cells have degenerated.
In rare cases, there may be no excellent quality embryos, in which case the doctor and embryologist must decide if any of your embryos can realistically progress to a safe pregnancy.
If this occurs, you can consider donating the embryos for training reasons, allowing healthcare workers to learn about and practice the processes involved in fertility therapy. For further information, please contact your clinic.
How Long Can My Embryos Be Stored For?
The conventional storage term for embryos is 10 years, however under specific conditions, women can retain their embryos for up to 55 years. Your clinician will be able to tell you whether or not you are able to do so.
If your address changes, you must notify the clinic. This is critical because if the clinic cannot reach you by the end of your agreed-upon storage term, they may have to remove your embryos from storage and allow them to perish.
If you have the option to preserve your embryos for 55 years, you must affirm that you wish to continue saving them, and your doctor must certify that you are qualified to do so. Again, staying in touch with your clinic is critical to preventing your embryos from being discarded if your storage space runs out.
How much control do I have over what happens to my embryos?
Before your embryos are frozen, it is critical that you provide your informed permission by completing the appropriate consent paperwork. These will clarify:
- How long you want the embryos to be stored for.
- What happens to your embryos if you or your partner dies or becomes unable to make decisions for yourself.
- Whether the embryos are to be used for your own treatment only, or if they can be donated for someone else's treatment or used for research .
- Any other conditions you may have for the use of your embryos.
What Happens Prior to Use or Implantation?
It's essentially a backwards procedure. The most important thing to remember when freezing a cell is to rehydrate it without blowing it up. Instead of using a machine, we warm them in air and a water bath, and the warming pace is less accurate and considerably faster than the cooling rate. Embryos are sent through a series of processes to gradually dilute away the cryoprotectants introduced when they were frozen. The cryoprotectant is gradually diluted when the cells are warmed to room temperature and ultimately to body temperature. They are then essentially left to rest before being implanted two to four hours after attaining body temperature.
It should be noted that effective sperm freezing occurred far before any other sort of cell freezing. Sperm is readily frozen because it lacks cytoplasm and is thus immune to all of the above stated forms of damage.
What If I Don’t Use My Embryos?
- You may either throw them away or donate them (to someone else or for use in research or training). In all circumstances, you and your partner/donor must grant written approval. Your clinic should supply the necessary documents.
- Donate them to someone else: By donating your embryos to someone in need, you are giving someone the most valuable gift of all.
- Donate them to science: Egg, sperm, and embryo research is crucial in assisting scientists in understanding the reasons of infertility and developing novel therapies.
- Donate them to training: Trainee embryologists need embryos to practice techniques, such as removing cells from embryos and mastering the freezing/thawing process.
- Discard them: Some people prefer to discard their embryos. Embryos that are no longer needed are simply removed from the freezer and allowed to perish naturally in warmer temperatures or water.
Advantages of Embryo Cryopreservation
Embryo freezing can help people get pregnant later in life if they are facing current barriers, such as:
- Advancing age.
- Gender transition.
- Infertility issues.
- Social/personal reasons like if you’re pursuing higher level education or have professional demands and plan to delay pregnancy for several years.
- Treatment that may damage fertility (for example, chemotherapy or pelvic radiation therapy for cancer).
- Upcoming military deployment.
- Women without a partner may be concerned about advancing age and choose to either freeze eggs or embryos that they create with donor sperm.
Risks or Complications of This Procedure
Embryo freezing does not offer any hazards to subsequent pregnancies, such as congenital defects or health concerns. In reality, studies on the outcomes of frozen-thawed embryos reveal decreased rates of preterm delivery, low birth weight, growth limitation, and perinatal death.
The main risks associated with embryo cryopreservation are:
- Embryos are harmed during the freezing process.
- Embryos that are unsuitable for freezing
- Failure to conceive after embryos have been thawed and implanted.
- Increased incidence of pregnancy-related medical complications such as preeclampsia and placenta accrete spectrum.
- Multiple births are possible if more than one embryo is implanted (twins or triplets).
What Happens Before Embryo Cryopreservation?
You must give authorization to freeze embryos. You will be given consent paperwork to read and sign by your healthcare professional. The papers should include information such as:
- The number of embryos that will be frozen.
- How long will they be kept? (often 10 years).
- What happens when the storage timer runs out?
- What happens if you die or become incapacitated before the storage time expires?
- What uses are permissible for embryos (for example, only your fertility treatments or if they can be donated to research or to another infertile couple).
Your healthcare practitioner can also advise you on the ideal embryonic stage to freeze one or more embryos. The following phases are susceptible to freezing:
- Cleavage stage: When the single cell has multiplied to between four and eight cells after about 72 hours.
- Blastocyst stage: When the single cell has multiplied to between 200 to 300 cells after five to seven days.
Difference Between Blastocyst & Cleavage Transfers?
The difference is that because blastocyst embryos may grow for longer in the lab, the embryologist can more easily pick the embryos that are most likely to implant in the womb. This implies that blastocyst transfers have a greater birth rate.
However, not all embryos that reach the blastocyst stage will survive, and in certain situations, a couple may have no embryos to transfer to the womb. There's no way of knowing if the embryo could have continued to a successful pregnancy if it had been transplanted at an earlier cleavage stage.
What Happens During Embryo Cryopreservation?
There are two methods to freeze embryos: vitrification and slow freezing.
- In vitrification, fertility professionals:
- Add a cryoprotective agent (CPA) to the embryos. CPA is a liquid that acts like antifreeze and protects cells from ice crystals.
- Place the embryos immediately into tanks of liquid nitrogen at -321° Fahrenheit (-196.1° Celsius).
- Slow freezing has fallen out of favor, but some fertility specialists may still use it. In slow freezing, fertility professionals:
- Add less cryoprotective agent (CPA) to the embryos than was used in vitrification.
- Place the embryos in a cooling unit that gradually lowers the temperature over a two-hour period.
- Remove the embryos from the cooler and place them in liquid nitrogen tanks set to -321° F (-196.1° C).
For either process, the embryos are:
- Containers resembling little straws are used.
- Labeled with information that identifies them as yours.
Surprisingly, the embryos retain their biological age after being frozen. So, if you freeze them at 35 and then use them at 50, the embryo hasn't aged.
What Happens After Embryo Freezing?
When it comes time to use the frozen embryos, a fertility expert will:
- Remove the embryos from the liquid nitrogen.
- Allow them to recover to normal temperature gradually.
- Soak them to get rid of the CPA.
- Use the embryos as directed (for example, transfer them into your uterus).
Success Rates of Embryo Storage
After cryopreservation, the procedure of thawing an embryo has a reasonably high success rate, and research shows that women who use thawed embryos have a fair probability of having healthy infants.
A comparative studyTrusted Source and review published in 2016 found no increase in developmental problems in newborns delivered following cryopreservation. However, further long-term follow-up studies are still required by the medical community.
According to Trusted Source, as compared to gradual freezing, vitrification boosts an embryo's chances of survival both during the freezing stage and throughout thawing.
Frozen or Fresh Embryos?
A research published in the International Journal of Reproductive Biomedicine examined the outcomes of over 1,000 cases of embryo transfer using either fresh or frozen embryos.
In terms of pregnancy rates or fetal health, the researchers discovered no statistical difference between the kinds of embryos. The scientists pointed out that in the future, patients may employ frozen embryos rather than fresh embryos for additional transfers.
According to other research, transplanting frozen embryos may be more effective.
According to the findings of a 2014 study, frozen embryo transfer may result in a greater rate of pregnancy and better outcomes for both the mom and the infant.
Embryos storage is another method for preserving future fertility. Some people chose this operation because they are undergoing hormone therapy, cancer treatment, gender affirmation surgery, or another medical procedure that impacts their fertility.
In some cases, your doctor may advise you to freeze your embryos to reduce the risk of ovarian hyperstimulation syndrome, which can worsen after pregnancy. If certain hormone levels are excessively high during the IVF cycle, it may also be advised to assist boost the chances of conception.
Frozen embryos are preserved and monitored at medical facilities, generally a laboratory, or commercial reproductive medicine institutions. They may be securely stored for up to ten years, if not longer.
The likelihood of pregnancy following embryo transfer is mostly determined by the woman's age at the time the embryos are generated. Procedures that use eggs obtained from persons aged 35 or younger have the best probability of producing a pregnancy. More than 95% of frozen embryos survive the thawing process.
Complications from anesthesia and infection, as well as injury to the bladder, intestine, or a blood artery from the needle and catheter, are risks connected with egg retrieval procedures. These occurrences are quite unusual. When the ovaries are overstimulated by the drugs, a condition known as ovarian hyperstimulation syndrome can arise. For these reasons, patients are constantly watched throughout the procedure.