Egg freezing, known scientifically as oocyte cryopreservation, offers individuals a method to preserve their fertility for future use. This process allows for the storage of unfertilized eggs, providing an option for those who wish to delay childbearing. Freezing eggs at a younger age can enhance the chances of conceiving later in life, addressing personal or medical considerations.
The Egg Freezing Process
Egg freezing begins with ovarian stimulation, where individuals administer hormone injections daily for about 10 to 14 days. These medications encourage the ovaries to produce multiple mature eggs, rather than the single egg typically released during a natural cycle. Regular monitoring appointments involve ultrasounds and blood tests to track the growth of follicles and hormone levels, allowing fertility specialists to adjust medication dosages as needed.
Once the eggs are deemed mature, a final injection, often called a “trigger shot,” is given to prompt their readiness for retrieval. Approximately 34 to 36 hours later, the egg retrieval procedure takes place. This minor outpatient surgical procedure is performed under light sedation or anesthesia, involving the use of a transvaginal ultrasound to guide a thin needle into the ovarian follicles to collect the eggs. Immediately following retrieval, mature eggs are quickly frozen using a flash-freezing technique called vitrification, which prevents ice crystal formation and preserves their viability for long-term storage in liquid nitrogen.
Factors Affecting Egg Freezing Success
Several biological factors influence egg freezing success and the number of viable eggs retrieved. Age at freezing is a primary consideration. Younger individuals generally yield more higher-quality eggs, increasing the likelihood of successful pregnancy. Egg quantity and quality naturally decline with age, accelerating in the late 30s and early 40s.
Ovarian reserve, a woman’s existing egg supply, also substantially determines the number of eggs collected per cycle. Tests like Anti-Müllerian Hormone (AMH) levels and antral follicle count (AFC) provide insights into this reserve. Egg quality deteriorates with age, leading to more genetically abnormal eggs in older individuals. These abnormalities can affect an egg’s ability to fertilize, develop into a healthy embryo, or result in a successful pregnancy.
Estimating Eggs for One Baby
Estimating the number of frozen eggs needed for one live birth involves considering statistical probabilities and attrition rates. Research provides general guidelines based on age at the time of freezing. For women under 35, freezing around 15 mature eggs offers a cumulative 80% chance of at least one live birth. Some studies suggest that for women under 35, 9 eggs may provide a 70% chance of one live birth.
For those aged 35 to 37, about 20 mature eggs are often recommended for an 80% chance of live birth. Women aged 38 to 40 may need to freeze around 30 mature eggs for a 75% chance. These numbers account for losses at each stage: 90-95% of vitrified eggs typically survive thawing, and about 70% of thawed eggs fertilize. Not all fertilized eggs develop into viable embryos or lead to successful implantation and pregnancy.
Projecting Eggs for Two Babies
When considering two successful pregnancies from frozen eggs, the required number generally increases multiplicatively. A higher quantity is necessary to achieve two separate live births, accounting for attrition across multiple attempts or pregnancies. Each attempt to conceive, whether for a first or second child, involves the same stages of thawing, fertilization, embryo development, and transfer, each with its own probabilities of success.
For women 37 and younger, freezing 15 to 20 mature eggs is estimated to provide up to a 50% chance of two children. For women aged 38 to 40, freezing 25 to 30 mature eggs might offer up to a 40% chance. These projections highlight the increased complexity and need for a larger egg reserve to navigate losses and ensure sufficient viable embryos for two distinct pregnancies. These are statistical estimates, and individual outcomes can vary based on factors like egg quality and overall health.
Beyond Freezing: Using Your Eggs
Once the decision is made to use frozen eggs, the process typically involves several steps to achieve a potential pregnancy. The preserved eggs are thawed, with modern vitrification techniques yielding high survival rates, often ranging from 90% to 95%. Following thawing, the eggs are fertilized in a laboratory setting using In Vitro Fertilization (IVF), often through intracytoplasmic sperm injection (ICSI), where a single sperm is injected into each egg.
The fertilized eggs develop into embryos over several days, with embryologists monitoring growth and selecting the most viable. One or more selected embryos are then transferred into the uterus. A waiting period follows before a pregnancy test.
Consulting with a fertility specialist throughout this process is recommended. They provide personalized guidance, assess individual circumstances, and help navigate the complexities of using frozen eggs for conception.