Why Do Some Frozen Eggs Not Make It Through the Thaw? Understanding the Science and Realities of Egg Freezing

Egg freezing has become an increasingly popular option for those looking to preserve their fertility, whether for medical reasons, personal timing, or future family planning. The process, known as oocyte cryopreservation, offers hope and flexibility, but it’s not without its uncertainties. One common question we hear is: Why do some frozen eggs not survive the thaw? It’s a great question, and understanding the answer requires a look at the science behind egg freezing, the challenges of the process, and the factors that influence success rates.

In this article, we’ll explore the reasons why some eggs don’t make it through the thawing process, what happens during freezing and thawing, and how advancements in technology are improving outcomes. We’ll also discuss what you can do to set yourself up for the best possible results. While egg freezing is a powerful tool, it’s important to approach it with realistic expectations and a clear understanding of the process.

The basics of egg freezing and thawing

Egg freezing involves carefully extracting eggs from the ovaries, cooling them to sub-zero temperatures, and storing them for future use. The goal is to preserve the eggs in their current state, effectively hitting the “pause” button on those specific eggs. When you’re ready to use them, the eggs are thawed, fertilized, and transferred as embryos in the hopes of achieving a pregnancy.

The freezing process itself has come a long way. In the past, a method called slow freezing was used, but it often led to the formation of ice crystals, which could damage the eggs. Today, most clinics use a technique called vitrification, which flash-freezes the eggs so quickly that ice crystals don’t have time to form. This method has significantly improved survival rates, but it’s not foolproof.

What percent of eggs make it through the thaw?

What what are the chances your eggs will survive the thaw? The answer isn’t straightforward, as survival rates can vary based on several factors, including the clinic’s expertise, the age of the eggs, and the freezing method used. 

Overall, the survival rate when thawing frozen eggs using vitrification is 95%. This is a significant improvement over older methods like slow freezing, which had survival rates closer to 75%. Vitrification’s rapid cooling process minimizes the risk of ice crystal formation, which is a major cause of egg damage during freezing and thawing.

Why some eggs don’t survive the thaw

In general, thaw rates are very good these days. However, they aren’t the same for everyone. Even with the advancements in vitrification, not all eggs make it through the thawing process. Here are some of the key reasons why:

• The fragility of eggs: Human eggs are among the largest cells in the body and contain a high amount of water. This makes them particularly sensitive to temperature changes. During freezing and thawing, the egg’s structure can be compromised, leading to damage that prevents it from surviving.
• Age and quality of the eggs: The quality of the eggs at the time of freezing plays a significant role in their survival. Younger eggs, typically from women in their 20s and early 30s, tend to have better survival rates than those from older individuals. This is because younger eggs are more likely to have intact DNA and cellular structures, which are better able to withstand the stresses of freezing and thawing.
• Laboratory quality: The process of freezing and thawing eggs is highly technical and requires precision. Even small errors in the timing, temperature, or handling of the eggs can impact their viability. Clinics with experienced embryologists and state-of-the-art equipment tend to have higher success rates.

Survival rates can and do vary between clinics. Clinics with highly skilled embryologists and advanced technology often report higher success rates. Some top-tier fertility clinics report near perfect survival rates for eggs frozen using vitrification. This is why it’s so important to choose a clinic with a strong track record and transparent data.

What happens after the eggs are thawed

Surviving the thaw is just the first step. After thawing, the eggs must be fertilized, develop into healthy embryos, and successfully implant in the uterus. Estimates vary, but according to UCLA Health the overall chance of a pregnancy is between 4-12% per oocyte per thawed egg, depending on factors like age, sperm quality, and clinic expertise. This means that while most eggs survive the thaw, not all will result in a successful pregnancy.

To put this into perspective, if you freeze 10 eggs, you might expect 8-9 to survive the thaw. Of those, only a portion may fertilize and develop into viable embryos. Your fertility doctor can work with you to determine the ideal number of eggs to freeze to increase the likelihood of achieving a pregnancy in the future.

While these numbers might feel daunting, it’s important to remember that egg freezing is still one of the most effective ways to preserve fertility, especially for those who freeze their eggs at a younger age. Advances in technology and clinic expertise continue to improve outcomes, offering hope and options for those planning for their future families.

What you can do to improve your chances

While some factors, like age, are beyond your control, there are steps you can take to improve your chances of success:

• Choose the right clinic: Research clinics thoroughly and choose one with a strong track record in egg freezing and thawing.
• Freeze your eggs sooner rather than later: The younger you are when you freeze your eggs, the better their quality and survival rate.
• Follow your clinic’s instructions: During the egg retrieval process, follow your clinic’s guidelines for medications, diet, and lifestyle to ensure the best possible egg quality.
• Consider undergoing multiple cycles: The more eggs you freeze, the higher your chances of having viable eggs after thawing. 

Read more in How to Increase Egg Freezing Chances of Success

The future of egg freezing technology

While egg freezing has come a long way, there’s still room for improvement. Researchers are continually working on new techniques to improve survival rates and make the process more reliable. For example, some studies are exploring the use of different cryoprotectants or modified freezing protocols to further reduce the risk of damage.

Advances in artificial intelligence and machine learning are also being applied to fertility treatments. These technologies could help embryologists better predict which eggs are most likely to survive freezing and thawing, leading to more personalized and effective treatments.

Final thoughts

Egg freezing offers hope and flexibility for those looking to preserve their fertility, but it’s not without its challenges. Understanding why some eggs don’t survive the thaw can help you make informed decisions and set realistic expectations. By choosing a reputable clinic, freezing your eggs at a younger age, and staying informed about the process, you can improve your chances of success.

While the science of egg freezing continues to evolve, it’s important to remember that every individual’s experience is unique. If you’re considering egg freezing, take the time to consult with a fertility specialist, ask questions, and weigh your options carefully. With the right information and support, you can make the best choice for your future.

Freeze your eggs with Cofertility

We’d love the opportunity to support you on your egg freezing journey.

Through our Split program, qualified freezers can freeze their eggs for free when donating half of the eggs retrieved to a family who can’t otherwise conceive.

Through our Keep program — where you keep 100% of eggs retrieved for your own future use — we offer exclusive discounts on expenses, such as frozen egg storage. Keep members also still gain free access to our Freeze by Co Community, a safe space for those engaging in the egg freezing process (or gearing up for it) to connect and lean on each other.

By making egg freezing easier and more accessible, our programs further strengthen the American Society of Reproductive Medicine (ASRM)’s Committee Opinion that egg freezing can help promote social justice and strengthen gender equality.