How Long Can Embryos Be Frozen and How Does It Affect the Success Rate?

Freezing embryos, also referred to as cryopreservation, is a common fertility preservation measure that allows an individual to begin or add to their family in the future. Whether you are using your own eggs or donor eggs, you’re probably wondering how long can embryos be frozen to still be viable. Keep reading this guide on embryo freezing to understand how cryopreservation works, how the egg retrieval process is influenced by it, and how successful embryo freezing is overall.

 

 

How Does Embryo Freezing Work?

To begin, it’s important to understand what an embryo is and how it differs from an egg. An embryo is an egg that has been fertilized by sperm, and represents the earliest stage of human development.

To create an embryo for freezing, a fertility specialist must first perform an egg retrieval. During the retrieval, you or an egg donor are placed under twilight sedation with the use of anesthesia, while the specialist safely retrieves the matured eggs that are present in the ovaries at that time. These unfertilized eggs can be frozen through a process called vitrification to create an embryo later. This is a common practice when you are receiving donor eggs. 

Alternatively, eggs can be retrieved and used for embryo creation within 3-5 days in a process called Fresh Embryo Transfer. Rather than freezing the egg, the embryologist can fertilize an egg with sperm from a partner to later be transferred back into the uterus. Prior to the embryo being transferred, it is monitored as it grows under a petri dish for 5-7 days. The embryo can be tested for genetic conditions, then graded depending on the likelihood of successful growth once implanted. From there, the embryo can be frozen (cryopreserved) through vitrification.

 

The Vitrification Process

Initially, embryos were preserved through a “slow freezing” process. The embryo would be slowly cooled until the biological processes of development halted. Slow freezing was an effective method for sperm and embryos, however, it posed a problem for eggs. Since eggs contain a high level of water compared to sperm and embryos, ice crystals would form on the eggs during the freezing process, making them less likely to result in a successful pregnancy.

Scientists then developed vitrification, or “fast freezing,” to combat the problems of freezing eggs. Vitrification works so well that it is also used for freezing embryos and sperm.

During verification, an embryo is bathed in an antifreeze solution for a very short amount of time while it is instantaneously frozen. It is then placed in a special cryogenic freezer until it’s time to be used.

Embryos are typically frozen by Day 5 or Day 6 after the egg is successfully fertilized. This is because at this point, the embryo has a stronger chance of surviving the freeze and subsequent thawing process. Also, it’s easier to tell which embryos are higher quality and should be frozen.

 

How Long Can Embryos Be Frozen?

From a scientific standpoint, embryos can be frozen for a seemingly unlimited amount of time. Storage in liquid nitrogen ensures that embryos are not warmed enough to restart any biological development. 

Currently, most people use an embryo within five years, with the longest storage time on record being 30 years.

 

Frozen Embryo Transfer Success Rate

When you have made the decision to move forward with an embryo transfer and have coordinated with your doctor, the embryo is carefully thawed and transferred to the uterus of the individual who will carry the child to term. If your eggs come from someone under 35 years old (whether that individual is you or an egg donor), embryos have up to a 95% thaw survival rate, according to John Hopkins Medical Journal.

According to 2020 IVF success rate data from the Center for Disease Control, frozen embryo transfer has a national success rate of 44.5% singleton births (singleton births are the birth of one child at a time).

This is on par with successful pregnancies using fresh or frozen donor eggs, as well as people under 35 who used their own eggs for IVF. This means that using frozen embryos is just about as successful as other methods of IVF.

 

Fresh vs. Frozen Eggs For Embryo Freezing

Some individuals opt to use frozen eggs over fresh eggs.

There are a number of reasons recipients elect to use frozen eggs:

• Lower Costs
• Easier Timing
• Guaranteed Quality Eggs
• The ability to choose from a wider selection of donors

But are frozen eggs just as viable for embryo creation and freezing as fresh ones?

The success rate of freezing embryos is highly dependent on the quality of the egg being used. The largest study on the use of fresh vs. frozen eggs in IVF shows that fresh eggs have a slightly higher success rate than frozen. However, how an egg is frozen will affect the overall quality of eggs. Many fertility clinics outsource egg freezing, which can lead to oversight, especially when it comes to preserving eggs while they’re being shipped to a fertility clinic. Oversight leads to poorer egg quality on average and less likelihood of successful embryo creation and freeze.

We are unique to other egg banks in that we are one of the only egg banks in the world who do not outsource our eggs. All eggs are retrieved, vitrified, and stored in our singular facility in Scottsdale, Arizona.

 

Preserving Frozen Eggs During Shipping

Shipping frozen eggs is a delicate matter. Eggs must stay below -320 degrees Fahrenheit to ensure that the egg does not begin any biological activity and does not age past the point of viable fertilization. It’s also crucial that the eggs a clinic receives are the ones purchased and there are no mistakes in the paperwork.

If you decide to use donor eggs from an egg and sperm bank, or your clinic decides to outsource egg freezing, the facility doing the vitrification needs to enforce proper shipping practices.

This means taking the utmost care in:

• Packaging frozen eggs
• Ensuring the proper temperatures are maintained during shipping
• Seeing that your eggs are properly transferred from the delivery vehicle to a freezer in your fertility clinic

The best way to ensure a viable embryo is to use high-quality eggs, and to do that is to source high-quality eggs from a focused, dedicated egg bank. 

 

 

Connect With Us

The World Egg and Sperm Bank is a state-of-the-art facility that focuses solely on providing donor gametes to future parents. We handle every step of egg retrieval, vitrification, and shipping to ensure that future parents-to-be get a viable egg without any uncertainty that comes with outsourcing donor egg freezing or transportation. 

If you are considering using donor eggs to conceive, read our getting started guide for intended parents and our post on finding the right egg donor.

We’re here to support future parents during every step of the way. If you have any questions regarding how long can embryos be frozen or about our facility or processes, do not hesitate to contact The World Egg and Sperm Bank.

 

Follow us on our socials!

Check out our Instagram, Facebook, and LinkedIn pages to see our content and learn more!