Oocyte cryopreservation, commonly known as egg freezing, is a medical procedure that preserves reproductive potential for future use. The decision to undergo retrieval and freezing is often deeply personal and significant. Once the eggs are safely cryopreserved, the focus shifts from the immediate medical procedure to long-term logistics, medical processes, and legal planning. This involves understanding how the eggs are maintained, the steps required for their eventual use, the statistical likelihood of success, and the necessary legal agreements for their disposition.
Long-Term Storage and Maintenance
Immediately following retrieval, mature eggs are preserved using vitrification, a flash-freezing technique. This method rapidly cools the eggs to the temperature of liquid nitrogen, approximately -196°C, preventing the formation of damaging ice crystals. The preserved eggs are stored in specialized cryogenic containers called dewars, which maintain this ultra-low temperature.
This storage effectively halts all biological activity, meaning the eggs do not age beyond the point of retrieval. Theoretically, the duration of storage is indefinite, as egg quality remains stable if the temperature is consistently maintained. Most patients store their eggs at the retrieval clinic or transfer them to a specialized, high-security cryobank facility.
Storage involves recurring annual charges to cover the maintenance, monitoring, and security of the cryobank. These annual storage fees typically range from $500 to $1,200, though costs vary based on the facility and location. Some facilities offer discounted rates if a patient prepays for multiple years of storage. If a patient decides to move the eggs, a specialized transportation service transfers the dewars under continuous cryogenic conditions to the new location.
The Process of Utilization
When the time comes to use the frozen eggs, the patient initiates a treatment cycle by preparing the uterine lining. This involves estrogen and progesterone medication designed to thicken the endometrium to an optimal receptive state, typically between 7 and 10 millimeters. The eggs are not thawed until the patient’s body is ready to receive an embryo.
The thawing process, or vitrification reversal, is a delicate and rapid procedure using warming solutions to bring the eggs back to body temperature. Post-thaw survival rates are commonly reported around 90%. After thawing, the eggs must be fertilized immediately because the freezing process requires the removal of protective cumulus cells, making the egg more vulnerable.
Fertilization of thawed eggs is almost universally performed using Intracytoplasmic Sperm Injection (ICSI). In ICSI, a single, selected sperm is injected directly into the center of each mature egg. This technique bypasses any potential hardening of the egg’s outer shell that can occur during freezing and thawing. Successfully fertilized eggs become embryos and are cultured for five to seven days, ideally reaching the blastocyst stage.
The final step is the embryo transfer, a non-surgical procedure where the best-quality embryo is loaded into a thin catheter. Using ultrasound guidance, the physician gently deposits the embryo into the prepared uterine cavity. A pregnancy test is scheduled about two weeks after transfer to determine if the embryo has successfully implanted.
Success Rates and Determining Factors
The probability of achieving a live birth using frozen eggs is primarily determined by the patient’s age when the eggs were frozen, not the age when they are thawed and used. Egg quality declines as a woman ages, so eggs frozen in the early 30s have a higher potential for success than those frozen later.
A significant number of eggs are required to maximize the chance of success due to attrition at each step. Approximately 90% of eggs survive the thaw, and of those survivors, about 70% successfully fertilize with ICSI. Only about 40% of fertilized eggs are expected to develop into blastocysts suitable for transfer.
For a woman under 35, freezing around 10 mature eggs may offer a live birth rate between 30% and 45%. This rate improves to 70% or more for those who freeze 20 or more eggs when under age 38. As age increases, the necessary number of eggs to achieve comparable success also rises. Other factors influencing the final outcome include the specific experience of the embryology laboratory and the health of the patient’s uterus at the time of transfer.
Legal and Disposition Considerations
Long-term storage requires a clear legal framework established through mandatory consent forms signed by the patient. These forms outline the rights and responsibilities associated with the stored eggs, including the terms of annual storage and payment. The patient must provide explicit instructions for the disposition of the eggs under various future circumstances.
The most important instructions cover the disposition of the eggs in the event of the patient’s death or permanent incapacitation. The patient must select from main options: discarding the eggs, donating them for scientific research, or donating them to another individual or couple for reproductive use. Regulations govern the donation process, requiring specific screening and testing protocols.
These consent documents are often reviewed annually and should be updated promptly if a patient’s life circumstances change, such as divorce or a change in health status. Including the disposition instructions in a personal will can help prevent future legal disputes, ensuring the patient’s wishes for their frozen biological material are legally recognized.