Oocyte cryopreservation, or egg freezing, is a proactive step toward preserving future fertility options. Determining the target number of eggs required for a live birth is complex because the calculation is based on probability. Success depends on the person’s age at the time of freezing and the attrition rate that occurs during later processes. Physicians use data-driven benchmarks to counsel patients, focusing on a strategic plan for banking enough eggs rather than a single retrieval.
Statistical Benchmarks for Live Birth Success
The likelihood of achieving a live birth from frozen eggs is tied directly to the number of eggs banked, modeled using clinical probability curves. Not every egg retrieved will result in a live birth, as several stages of attrition occur after thawing. Approximately 90% of frozen eggs survive thawing, but only about 70% of those will successfully fertilize with sperm. Further attrition occurs as fertilized eggs develop into a viable embryo, or blastocyst, which is the stage ready for transfer.
For a person under 35, freezing 10 to 15 mature eggs offers a 60% to 70% chance of achieving one live birth. Banking 20 eggs for this age group raises the chance of one live birth to approximately 85% to 90%. These probabilities decline noticeably with age; for example, a 10-egg cohort frozen at age 40 may only offer a 30% chance of a live birth. The strategic goal is typically to bank 15 to 20 eggs for those in their early to mid-thirties to ensure a high probability of success.
How Age Impacts Egg Quality and Quantity Needed
The primary factor driving the need for more eggs in older patients is the progressive decline in oocyte quality linked to maternal age. This decline is due to an increase in chromosomal abnormalities, known as aneuploidy. Aneuploid eggs carry an incorrect number of chromosomes and are highly unlikely to result in a viable pregnancy.
A younger patient in her early thirties may have approximately 75% chromosomally normal (euploid) eggs, requiring fewer eggs for success. Conversely, a patient freezing eggs at age 40 sees a sharp drop in quality, with the proportion of euploid eggs potentially falling below 50%. This difference means older patients must freeze a larger volume of eggs to compensate for the higher rate of non-viable ones. For example, achieving a 70% chance of live birth might require 10 eggs for a 34-year-old but 20 eggs for a 37-year-old. Past age 40, the quantity needed increases exponentially, often necessitating multiple retrieval cycles.
Clinical Assessments of Individual Ovarian Reserve
While statistical benchmarks define the need for eggs, clinical assessments determine an individual’s ability to produce that number per retrieval cycle. These diagnostic tools measure ovarian reserve—the functional capacity of the ovary and the pool of remaining eggs. They help physicians estimate potential egg yield and guide patients on how many cycles may be required to meet their target.
The two main metrics used are the Anti-Müllerian Hormone (AMH) blood test and the Antral Follicle Count (AFC) via transvaginal ultrasound. AMH is a hormone secreted by the granulosa cells of small follicles, indicating the total resting egg supply. A higher AMH level correlates with a greater number of eggs that can be stimulated.
The AFC is performed early in the menstrual cycle, counting the small, fluid-filled sacs (follicles) visible on the ovaries. The AFC provides a direct, real-time snapshot of the number of follicles ready to respond to stimulation medication and is considered one of the strongest predictors of the actual egg yield. For example, if a physician counts 15 antral follicles, the patient can reasonably expect a yield of around 10 to 15 mature eggs in that cycle. These tests measure quantity, not quality, but they are instrumental in creating a personalized treatment plan and projecting the number of cycles necessary to bank a statistically sufficient number of eggs.