The decision to freeze eggs, known technically as oocyte cryopreservation, involves retrieving mature eggs, flash-freezing them using vitrification, and storing them at extremely low temperatures. Once this initial process is complete, the focus shifts to the future usage and management of the stored eggs. This journey involves navigating the practical aspects of storage, understanding the technical steps for future conception, and preparing for the legal decisions that accompany this stored potential.
Long-Term Storage and Viability
Once the eggs are frozen, they enter a state of near-biological stasis, maintained in specialized cryotanks submerged in liquid nitrogen at \(-196^\circ\) Celsius. This ultra-cold environment halts all biological activity, meaning the eggs do not age or degrade while frozen.
The theoretical maximum duration for storage is considered unlimited. Egg quality is determined by the age of the person at the time of freezing, not the duration of cryostorage. Storage is governed by the facility’s accreditation and the payment of annual fees, which typically range from $500 to $1,000 per year.
Patients should ensure the facility is a reputable cryobank or fertility center with robust monitoring protocols. Proper maintenance prevents temperature fluctuations that could compromise the eggs’ integrity. The administrative and financial commitment requires ongoing planning and attention to the annual storage contract.
The Process of Thawing and Fertilization
When the decision is made to use the eggs, the first technical step is rapid warming, which is the reverse of vitrification. This controlled process avoids the formation of damaging ice crystals within the cell structure. The survival rate after thawing is generally high, with most modern clinics reporting that 85–95% of vitrified eggs survive intact.
Eggs that successfully survive the thaw are prepared for fertilization using Intracytoplasmic Sperm Injection (ICSI). ICSI involves an embryologist selecting a single sperm and directly injecting it into the center of the egg. This direct injection is necessary because cryopreservation causes the egg’s outer shell, the zona pellucida, to harden.
The hardening of the zona pellucida prevents sperm from penetrating the egg naturally, which is why standard in vitro fertilization (IVF) is not used. By bypassing this hardened layer, ICSI ensures a fertilization rate comparable to fresh eggs, typically around 67–70% of the thawed and surviving eggs. The resulting fertilized eggs, now embryos, are cultured in the lab before a viable embryo is selected for uterine transfer.
Understanding Live Birth Success Rates
The ultimate measure of success, the live birth rate, depends heavily on the quality of the eggs at the time of freezing. The most influential factor determining the probability of a live birth is the age of the person when the eggs were collected. This is because egg quality is locked in at the time of cryopreservation, regardless of the person’s age when the eggs are used.
For individuals under 35 at the time of freezing, the prognosis is significantly better. Data suggests that freezing 10 to 15 mature eggs can lead to a live birth probability of 60% or higher. For example, a 32-year-old with five frozen eggs may have a 55% chance of a live birth, increasing to nearly 98% with 25 eggs. This highlights that a higher number of banked eggs directly correlates with increased cumulative success.
Success rates decline noticeably for eggs frozen later in life due to age-related decreases in egg quality. A 38-year-old who froze five eggs, for instance, may see her chance of a live birth drop to about 26%, though freezing 25 eggs still offers a substantial 77% chance. Across all ages and cycles, the live birth rate per embryo transfer is often cited in the range of 35%. It is important to distinguish this final live birth rate from the initial egg survival rate and fertilization rate.
Decisions Regarding Disposition and Ownership
Beyond the medical procedures, decisions surround the future disposition of any unused eggs. Every individual who freezes eggs must sign detailed legal consent forms, known as disposition agreements, at the time of cryopreservation. These documents outline the patient’s intentions for the eggs under various future circumstances.
These agreements cover several potential outcomes for the stored eggs: continued storage, donation, or destruction. Donation options include contributing the eggs to a recipient for reproductive purposes or donating them to science and medical research. If the eggs are not needed, the person can choose to have them removed from the cryotank and discarded.
The agreements also address the complex legal implications of ownership in the event of death or separation. For unfertilized eggs, the individual who provided them generally retains sole legal control. The signed disposition agreement is the legally binding document that determines the fate of the eggs.