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What Is Embryo Cryopreservation?

Newborn baby hands close up

Embryo freezing, also known as embryo cryopreservation, is a common procedure that many couples choose to undergo during their conception journey.

It is relatively safe and can often lead to a successful pregnancy and delivery later on.

But what exactly does the process entail? And what is the success rate of embryo cryopreservation? Here’s what you need to know about embryo freezing and whether it’s the right procedure for you.

The Embryo Cryopreservation Process

Embryo freezing is a way to preserve embryos for future use. It is part of most in vitro fertilization (IVF) and intra-cytoplasmic sperm injection (ICSI) processes.

When preparing embryos for storage, the embryos are cryopreserved and stored at an extremely low temperature, where they can remain for years. The embryos can later be thawed and transferred into the uterus.

Here are the steps required for embryo cryopreservation.

Step 1: Egg Retrieval

Typically, a woman releases one mature egg per ovulation cycle. To improve the chances of retrieving a viable egg for cryopreservation, the woman must first take hormone injections for 8-10 days, which will allow multiple eggs to mature and develop in the ovaries.

Retrieving the egg is a rather simple procedure that requires conscious anesthesia. It has minimal side effects, including mild cramping.

Step 2: Insemination

The next step in embryo cryopreservation is insemination. In order for an egg to become an embryo, it needs to be fertilized with sperm. The egg is inseminated in a petri dish and then, once fertilized, it must develop for 5-7 days.

More than one egg can be retrieved and inseminated. The number of embryos that are viable to freeze often depends on the woman’s age (more embryos are viable when the woman is under 35 years of age).

Step 3: Genetic Testing

Not all couples need to undergo this step, but it’s an option for people who want to test their embryos for genetic abnormalities.

Preimplantation genetic diagnosis (PGD) is especially useful when one parent is a carrier of a known genetic condition, such as Huntington’s Disease, because PGD can prevent you from unknowingly transferring the condition to your future child.

Step 4: Embryo Freezing

Before an embryo can be frozen, it must first go through cryopreservation. This entails removing water from the cell and replacing it with a cryoprotectant agent (CPA). This is to protect the cells from forming ice crystals.

There are two methods that fertility doctors can use for embryo freezing: slow freezing and vitrification.

Slow freezing involves placing the embryos in a sealed container and gradually lowering the temperature. While it prevents the embryos from aging and reduces the risk of damage, it’s rather time-consuming (it could take over two hours) and it’s an expensive process.

On the other hand, vitrification involves rapidly freezing the embryos and using much higher strengths of CPAs. The embryos are frozen so quickly that they don’t have time to form ice crystals, thus protecting the embryos and increasing the survival rate when thawed.

Approximately 95% of embryos survive the freezing process. After the embryo freezing process, they are stored in liquid nitrogen and can be frozen for many years.

Step 5: Embryo Transfer

The final step in embryo cryopreservation occurs when the woman or couple decides they want to conceive and therefore thaws the embryos.

The embryos are slowly thawed and soaked in special fluids to remove the CPAs and restore the cells’ natural water content.

Using a very soft catheter, and under ultrasound guidance, the embryo is gently inserted directly into the woman’s uterus with the hopes of becoming a successful pregnancy.

Why Are Embryos Cryopreserved?

There are many reasons why couples might choose embryo freezing. Here are a few of them:

Delaying Pregnancy

Sometimes, it boils down to timing. Nowadays, it’s common for women to want to focus on other aspects of their life first (e.g. their career) before conceiving a child. In this case, women might choose to freeze their eggs, so that they can be used at a later date.

As women age, the quality and quantity of their eggs decreases, especially after turning 35 years old. Since frozen embryos contain younger eggs, there is less risk of pregnancy complications should a woman choose to have a baby later in life.

Upcoming Medical Treatments

Other times embryo cryopreservation provides women who are undergoing medical treatments that might affect fertility (e.g. chemotherapy) the opportunity to save embryos and use them at a later date. It’s also common for women who have genetic disorders that could affect reproduction to want to freeze their embryos.

Additional Embryos

When a patient undergoes IVF, it’s common for multiple embryos to be created. Rather than destroying the extra embryos, couples may opt to freeze them instead. The couple can choose to use the frozen embryos later to have another child or they can be saved and given to someone else through a donor program.

Many same sex-couples and other LGBTQ+ people who wish to have children might opt for in vitro fertilization using a sperm donor or egg donor. Embryo freezing allows them to store their embryos to use at a later date, as well.

The Success Rate When Using Thawed Embryos

One of the benefits of embryo cryopreservation is that it provides the opportunity for fertility doctors to transfer embryos in the future without needing to retrieve eggs again.

The success rate for embryo cryopreservation is relatively high, which is why it’s a popular procedure. Research shows that babies born after cryopreservation show no increase in developmental abnormalities compared to babies born from fresh embryos; however, further long-term studies are required to confirm these findings.

Some research suggests that transferring frozen embryos as opposed to fresh embryos may actually increase the chances of a successful pregnancy and have better outcomes for both the mother and baby.

Risks & Side Effects when Extracting Embryos for Storage

Women who undergo embryo cryopreservation may experience mild side effects. Typically, any complications or side effects of embryo freezing will occur when the doctor is extracting the eggs.

Some of the common side effects include:

  • Cramping or bloating
  • Feeling full
  • Light bleeding
  • Changes in vaginal discharge
  • Infection
  • Overstimulation of the ovaries

While embryo freezing is a rather safe and straightforward procedure, one of the major risks associated with extracting embryos for storage is that it may result in multiple pregnancies. Multiple pregnancies could be associated with higher risk of complications for both the mother and fetus, which is why many fertility clinics recommend transferring only one embryo at a time for patients under 38 years of age.

ONE Fertility Kitchener Waterloo’s Embryo Storage Service

At ONE Fertility Kitchener Waterloo, our goal is to provide our patients with the best medical care and to support their needs as they embark on their fertility journey, whether that be through IVF, cycle monitoring, or embryo freezing. Our evidence-based medical approach and compassionate care ensure that our patients understand their treatment plan throughout the entire process and receive safe and high-quality fertility treatment with excellent success rates.

To learn more about our state-of-the-art fertility clinic, our treatment options, and counselling services, give us a call or send us an email and we would be happy to answer any questions you might have about our fertility services, including our embryo cryopreservation success rates.


4271 King St East, Suite 200
Kitchener, ON
N2P 2X7

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Saturday-Sunday: 8am-12pm

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Phone: 519.650.0011
Fax: 519.650.0033