Cryopreservation and the freezing of embryos are revolutionary technologies that have fundamentally changed the landscape of fertility therapies, allowing patients more options, enhanced rates of conception, and the ability to store reproductive tissue for use in later years. These have become essential components of assisted reproductive technologies (ART) such as In Vitro Fertilization (IVF), enabling patients to freeze eggs, sperm, and embryos for future use. More recent innovations in cryopreservation and embryo freezing processes have contributed to higher success rates with reduced risk factors and more efficient methods for storing and thawing reproductive biological material. 

In the following article, we will be looking at the most recent advances in cryopreservation and embryo freezing technology, their importance, and the effect they have on the success rates of fertility treatments. 

Cryopreservation and Embryo Freezing Explained 

Cryopreservation is the act of cooling biological material to very low temperatures to cease metabolic and biochemical activity. This chemical enables the preservation of cells, tissues, or embryos for potential future use without deterioration. Cryopreservation is now widely applied in fertility treatments and is employed to store eggs, sperm, embryos, and even ovarian or testicular tissue. Cryopreservation is the practice of employing extremely low temperatures to preserve the viability of cells and tissues, and embryo freezing is a specific application of this technology in which in vitro fertilized embryos are frozen until transfer. 

Cryopreservation allows fertility patients to:  

• Preserve fertility for future use: Women can freeze eggs before undergoing medical treatments like chemotherapy or radiation, or they can freeze embryos if they want to delay childbearing.
• Avoid ovarian hyperstimulation syndrome (OHSS): Cryopreservation allows for the option of freezing embryos rather than transferring them in the same cycle, helping patients with high-risk conditions like OHSS.
• Increase IVF success rates: Embryos can be frozen for later transfer, allowing patients to undergo multiple embryo transfers without undergoing additional ovarian stimulation cycles.

Recent Advances in Cryopreservation and Embryo Freezing  

Cryopreservation and embryo freezing technology have greatly advanced in the last few decades. As a result, frozen-embryo survival rates, thawed-embryo pregnancy rates, and freezing efficiency have all improved. Here are some notable advances in this area.

1. Vitrification: A Game Changer in Cryopreservation

Vitrification has been one of the key advances in cryopreservation technology in recent years. This technique, which has largely replaced slower freezing methods, involves freezing embryos or eggs rapidly by immersing them in a cryoprotectant solution and then cooling them rapidly. This rapid cooling process causes the liquid within the cells to solidify into a glass-like substance (thus the term “vitrification”), preventing the formation of ice crystals that can damage the cells. 

Vitrification has revolutionised cryopreservation in several ways:

• Higher survival rates: Vitrification results in significantly higher survival rates for thawed embryos and eggs. The slow freezing method used previously could lead to damage caused by ice crystals, which often resulted in poor embryo survival post-thaw. Vitrification reduces this risk by preventing ice formation.
• Improved pregnancy rates: Studies have indicated that embryos frozen using vitrification have a higher likelihood of leading to successful pregnancies compared to those frozen via slow freezing.
• Enhanced efficiency: Vitrification requires shorter exposure times and is more straightforward to implement, making it a faster and more efficient method for freezing reproductive material.

2. Improved Cryoprotectant Solutions  

Cryoprotectants prevent the formation of ice in the maturing oocyte during the freezing process. These solutions work by preventing ice crystals from forming in the cells, which can cause irreversible damage, and instead replace the water within those cells. Over time, there were improvements in cryoprotectant types and concentrations, and cryopreserved embryos and eggs improved.

• More effective cryoprotectants: Modern cryoprotectants are better able to protect embryos and eggs from damage during freezing and thawing. Research has led to the development of cryoprotectants that can reduce toxicity and enhance the overall viability of the reproductive material.
• Tailored cryoprotectants for different cell types: Different types of reproductive material, such as eggs, sperm, and embryos, respond differently to cryoprotectants. Developments have led to the creation of cryoprotectant solutions tailored to each type of reproductive cell, and sperm freezing has increased success rates. 

3. Cryopreservation of Ovarian Tissue and Oocytes  

Freezing oocytes (eggs) is an established practice; follicle or ovarian tissue cryopreservation is a newer and highly promising technique. Freezing ovarian tissue is especially advantageous for women who want to maintain their ability to have children before undergoing therapies like chemotherapy that can damage eggs.

• Ovarian tissue cryopreservation: The removal of ovarian tissue before a woman undergoes medical care, which can be frozen, with the tissue then transplanted into the body later. The ovarian tissue can then be re-implanted in a woman’s body to promote natural fertility. 
• Oocyte cryopreservation: Also known as egg freezing, oocyte cryopreservation is the freezing of unfertilized eggs (oocytes), which can be useful for women wanting to postpone motherhood. Improvements in freezing techniques have boosted the percentage of eggs that survive thawing, which in turn has improved the odds that a woman will become pregnant after thawing her eggs years later. 

4. Single-Embryo Transfer (SET) and Freeze-All Strategy 

Increasingly in IVF treatments, a single-embryo transfer (SET) is performed, when one embryo rather than several is placed in the uterus. This method lowers the chance of multiple pregnancies (for instance, twins or triplets) but increases the likelihood of a successful pregnancy with just one embryo. 

Extra embryos that aren't being used are kept frozen until they are needed, which is the common strategy of freeze- all, often combined with SET (single embryo transfer), meaning all embryos created in one IVF cycle are frozen at once instead of being moved into the womb in that cycle. Additionally, this strategy permits a woman's body time to recover from ovarian stimulation and the IVF procedure itself, which can help reduce the risk of complications such as ovarian hyperstimulation syndrome (OHSS). Freezing all embryos and transferring them at a later time also gives patients the benefit of time to evaluate the best embryo for transfer. 

• Benefits of freeze-all and SET: This approach has been associated with improved implantation rates, fewer complications, and better overall outcomes for women undergoing IVF.

5. Advancements in Thawing Techniques 

The thawing of cryopreserved embryos and eggs has long been a tricky business. In recent years, advances in the methods for thawing, such as controlled-rate thawing and post-thaw specific protocols, have increased the likelihood of the viable recovery of frozen reproductive material. 

• Controlled thawing: Innovations in controlled thawing systems allow embryologists to carefully manage the temperature and timing of the thawing process, ensuring that embryos and eggs are revived optimally, preserving their integrity and maximizing the chances of successful implantation.  
• Improved thawing techniques: The development of techniques that ensure a smoother and faster thawing process has further increased the efficiency of embryo freezing. For example, the use of sophisticated warming systems ensures that embryos survive the thawing process without damage, further improving pregnancy rates. 

Benefits of Cryopreservation and Embryo Freezing 

• Flexibility for Family Planning: Cryopreservation provides the ability to delay pregnancy, making it particularly beneficial for individuals who want to preserve their fertility while focusing on other aspects of life, such as career or education.
• Increased Success Rates: With advancements in embryo freezing, patients now have higher success rates when using frozen embryos. Many women also benefit from the opportunity to undergo multiple IVF cycles using previously frozen embryos, reducing the need for repeated stimulation cycles.
• Better Control Over Fertility: The ability to freeze eggs, sperm, or embryos offers greater control over reproductive health and allows for future planning with less pressure.

Conclusion

Cryopreservation and the technology for freezing embryos have dramatically changed the landscape of fertility treatment, affording patients more options, flexibility, and higher rates of success. Advancements in cryopreservation during the last couple of decades, such as the move to vitrification, more proficient cryoprotectants, and improved thawing and freezing techniques, have resulted in the survival of greater numbers of embryos and improved patient outcomes. It is good to know that ovarian tissue and also eggs can be frozen for future use, which is especially important for women that are undergoing treatment for medical conditions that can impact reproductive health. With advancements in technology, the future of fertility preservation is bright and full of potential, enabling individuals and couples with a desire to delay family building to do so on their own schedule.