Oocyte cryopreservation, commonly known as egg freezing, is a medical procedure for fertility preservation. It involves retrieving, freezing, and storing a woman’s eggs (oocytes) for potential use in an in vitro fertilization (IVF) cycle later. The goal is to safeguard the quality and quantity of eggs collected at a younger age, proactively addressing the natural decline that occurs over time. This process provides a future option for biological parenthood.
The Oocyte Cryopreservation Process
The process begins with ovarian stimulation, where injectable hormone medications are administered daily for approximately ten to fourteen days. These hormones prompt the ovaries to mature multiple egg-containing follicles in a single cycle, rather than the single egg typically released naturally. Regular monitoring via blood tests and ultrasound scans tracks the development and size of these follicles.
Once the follicles reach an appropriate size, a final injection is given to trigger the eggs’ final maturation. The eggs are then retrieved during a minor surgical procedure performed under light sedation. A physician uses a transvaginal ultrasound to guide a needle into the ovaries and gently aspirate the fluid from the follicles, which contains the mature eggs.
Following retrieval, the mature eggs are immediately prepared for storage using a flash-freezing technique called vitrification. This method rapidly cools the eggs to a temperature of -196°C in liquid nitrogen. This process prevents the formation of damaging ice crystals inside the cell, preserving the eggs for an indefinite period.
Success Rates Using Frozen Eggs
The likelihood of achieving a live birth using frozen eggs is highly dependent on two factors: the woman’s age when the eggs were collected and the total number of eggs stored. Eggs frozen at a younger age, typically before 35, possess higher quality, which translates to better outcomes. For instance, women under 35 who freeze 15 to 20 mature eggs are often given an estimated 70% to 80% chance of at least one live birth.
The journey to pregnancy begins by thawing the eggs, a process where typically around 90% of eggs survive the warming. The surviving eggs are then fertilized in a laboratory using a procedure called intracytoplasmic sperm injection (ICSI), where a single sperm is injected directly into each egg. The fertilization rate for thawed eggs is generally around 70%.
The resulting embryos are cultured for several days before a selected embryo is transferred into the woman’s uterus. Studies indicate that a single embryo created from eggs frozen by a woman under 35 has approximately a 45% chance of resulting in a clinical pregnancy. The final live birth rate depends on the number of frozen eggs that successfully navigate each stage, from thaw to implantation.
Fertility and Natural Conception Post-Freezing
A common concern is whether the egg freezing procedure depletes the remaining ovarian reserve or compromises a woman’s ability to conceive naturally later. The procedure does not negatively impact future unassisted fertility. During a normal menstrual cycle, a cohort of follicles begins to develop, but only one typically reaches full maturity, while the rest undergo a natural degeneration process called atresia.
The hormone injections used in egg freezing “rescue” many of these eggs that would have otherwise been lost. Therefore, the procedure does not use up eggs that would have been available for future natural conception. Following the procedure, the menstrual cycle and ovulation typically return to normal, and the remaining egg reserve is unaffected.
The primary factor influencing a woman’s ability to conceive naturally remains her age and underlying reproductive health conditions. For women who froze eggs due to non-medical reasons, their chance of future natural pregnancy is the same as any woman of the same age with a similar reproductive history. The frozen eggs function as an independent backup option to mitigate the risk of age-related fertility decline.
Candidacy and Timing Considerations
Egg freezing is a consideration for several groups of individuals, including those who wish to delay childbearing to pursue career goals or who have not yet found a partner. It is also an important option for medical preservation, such as for women facing cancer treatments like chemotherapy or radiation, which can significantly impair ovarian function. Genetic conditions that lead to early menopause can also make a woman a strong candidate for fertility preservation.
The timing of the procedure is crucial for maximizing potential success. While egg freezing is an option for women up to their early 40s, the ideal time is generally in the late twenties to early thirties. Freezing eggs when they are younger ensures a higher quality and quantity of eggs are collected, significantly improving the probability of a live birth later. Consulting with a fertility specialist allows for a personalized assessment of ovarian reserve and health factors to determine the optimal window.