Slow Freezing: The Early Method
Before vitrification, the slow-freezing method was the primary technique for egg cryopreservation. Developed in the 1980s, this method gradually cooled eggs at a controlled rate, using cryoprotectants to reduce ice crystal formation.
However, slow freezing had several limitations:
Ice Crystal Formation – Since eggs contain a high water content, slow freezing often led to ice crystals that could damage egg structure and cellular integrity.
Lower Survival Rates – Only 50-60% of eggs survived the thawing process (Practice Committee of ASRM, 2013).
Lower Success Rates – The chances of a successful pregnancy with slow-frozen eggs were significantly lower than with fresh eggs.
Due to these challenges, egg freezing was considered experimental until the development of vitrification.
Vitrification: The Breakthrough in Egg Freezing
In the early 2000s, vitrification transformed the field of cryopreservation. Unlike slow freezing, vitrification is a flash-freezing process that cools eggs almost instantly, preventing ice crystal formation.
How Vitrification Works
Before freezing, eggs are exposed to highly concentrated cryoprotectant solutions that remove intracellular water, reducing the risk of ice formation.
Eggs are then plunged directly into liquid nitrogen at -196°C, in a process of ultra-rapid cooling they are solidified into a glass-like state without ice crystal formation.
Once vitrified, eggs are stored in liquid nitrogen which enables them to be stored indefinitely without degradation.
Why Vitrification Is Superior
Survival Rates of Over 90% – Unlike slow freezing, which had a 50-60% survival rate, vitrification results in egg survival rates exceeding 90% (Cobo et al., 2016, Fertility and Sterility).
Higher Fertilization and Pregnancy Rates – Vitrification consistently shows significantly higher rates of fertilization compared to slow freezing, and no significant difference in pregnancy rates between embryos created using fresh and vitrified eggs making vitrification the preferred method for egg freezing today.
Better Outcomes for Women Over 35 – While freezing eggs earlier is ideal, vitrification improves outcomes even for women who freeze their eggs in their late 30s.
Success Rates of Vitrified Eggs in IVF
One of the most important questions for women considering egg freezing is: What are the chances of having a baby using frozen eggs?
Multiple studies have analyzed success rates using vitrified eggs:
Live Birth Rates Per Thawed Egg
Women under 35: 4-10% per egg
Women 36-39: 3-6% per egg
Women 40+: 1-3% per egg
(ASRM, 2022)
Clinical Pregnancy Rates Using Vitrified Eggs
Studies show pregnancy rates of 40-50% per embryo transfer using frozen eggs (Cobo et al., 2016).
No significant difference in success rates between fresh and vitrified eggs in IVF.
Because of these high success rates, major reproductive societies now consider vitrification the standard for egg freezing.
Is There an Optimal Age to Freeze Eggs?
Age plays a critical role in egg freezing success. Research consistently shows that freezing eggs before age 35 provides the best outcomes.
Age at Freezing | Recommended Number of Eggs for 1 Live Birth |
<35 | 10-15 eggs |
35-37 | 15-20 eggs |
38-40 | 20-30 eggs |
40+ | 30+ eggs |
(*Data from Goldman et al., 2017, Human Reproduction)
Because egg yield per cycle declines with age, women in their late 30s may need multiple retrieval cycles to store an adequate number of eggs.
Considerations and Limitations of Egg Freezing
While vitrification has dramatically improved the success of egg freezing, there are still important considerations:
No Absolute Guarantee of Pregnancy – While vitrification improves egg survival, success also depends on factors like sperm quality and uterine health.
Need for ICSI (Intracytoplasmic Sperm Injection) – Frozen eggs have a hardened outer shell, requiring ICSI to fertilize the eggs.
Cost and Accessibility – The average cost per egg freezing cycle in the United States is $15,000 in the U.S., with storage fees amounting to as much as $1,000 per year. This is why many women explore options abroad for more affordable, high quality options for egg freezing.
The Future of Fertility Preservation
Vitrification has revolutionized fertility preservation, making egg freezing a reliable option for women who want to extend their reproductive timeline. With egg survival rates exceeding 90% and pregnancy rates comparable to fresh eggs, vitrification ensures that women have a real opportunity to conceive later in life.
At Conceivable, we work exclusively with partner clinics that use vitrification, ensuring that every patient benefits from the latest advancements in egg freezing technology. Our carefully vetted clinics maintain rigorous quality standards and provide world-class care at a fraction of the cost of U.S. clinics.
If you’re interested in learning more about our quality assurance practices, how egg freezing and IVF abroad work, or how to take advantage of affordable fertility treatments in Europe, book a free consultation today. Our team is here to help you plan your journey with confidence.
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