Oocyte cryopreservation, commonly known as egg freezing, is a medical procedure that offers individuals the option to preserve their fertility for the future. The process involves retrieving eggs, flash-freezing them, and storing them until they are needed for potential fertilization. For many, age 37 represents a point where the urgency to consider this procedure becomes more pronounced due to biological realities. This decision naturally leads to the central question of how many eggs should be frozen to offer a reasonable chance of success later on.
Fertility Context at Age 37
The female reproductive window sees a significant shift around the mid-thirties, with age 37 marking a particularly accelerated phase of change. At birth, a female is born with her entire lifetime supply of eggs, and this quantity, known as the ovarian reserve, steadily decreases over time. By age 37, the average ovarian reserve is estimated to have declined to approximately 25,000 eggs, a substantial drop from the 300,000 to 400,000 present at adolescence.
The rate of egg loss accelerates sharply after age 37. Simultaneously, the quality of the remaining eggs diminishes more rapidly, characterized by a higher incidence of chromosomal abnormalities (aneuploidy). This decrease in quality can lead to reduced fertilization rates, a greater risk of miscarriage, or difficulties in embryo development. The biological reality at age 37 is a double challenge: fewer eggs are available, and a lower percentage of those eggs are genetically normal.
Calculating the Target Number of Frozen Eggs
The number of eggs a 37-year-old should freeze is determined by statistical models that account for expected attrition, including survival rate after thawing, fertilization rate, embryo development, and implantation rate. Clinical data suggests that achieving a high probability of at least one live birth—often targeted around 70 to 80%—requires freezing a specific range of mature eggs.
For a woman aged 37, the typical recommendation to achieve a 70% chance of one live birth is to retrieve and cryopreserve approximately 10 mature eggs. To push that probability higher, closer to the 80% mark, the number may need to be between 15 and 20 mature eggs. While this is a general clinical guideline based on population studies, the exact number needed can vary widely between individuals.
These numbers are the cumulative total of mature eggs, which may require more than one retrieval cycle to acquire. For example, studies show that a woman aged 35 to 37 on average retrieves about 17 eggs in one stimulation cycle. Since not all retrieved eggs will be mature or survive the thaw, a buffer is built into the target number to compensate for the higher proportion of chromosomally abnormal eggs typical at this age.
Individual Factors That Adjust the Target
While population data provides a statistical starting point, an individual’s target number is refined by specific biomarkers reflecting her unique ovarian health. Anti-Müllerian Hormone (AMH) is a widely used blood test produced by small follicles, serving as a reliable indicator of ovarian reserve (remaining egg quantity). A lower-than-average AMH level for a 37-year-old signals diminished ovarian reserve, suggesting she may need multiple cycles to reach the recommended target.
Follicle-Stimulating Hormone (FSH) is another relevant test, a pituitary hormone that stimulates the ovaries to produce eggs. An elevated FSH level, measured early in the menstrual cycle, indicates the ovaries are becoming less responsive, signaling diminished ovarian function. This may necessitate a higher target number of frozen eggs to account for potential quality concerns. These hormone levels, along with the Antral Follicle Count (AFC) determined by ultrasound, help specialists tailor the ovarian stimulation protocol and determine required retrieval cycles.
The Egg Retrieval and Storage Process
The process of egg freezing begins with hormonal stimulation, where injectable medications are administered for about 10 to 14 days to encourage the ovaries to mature multiple eggs in one cycle. Throughout this period, the development of the egg-containing follicles is closely monitored through regular blood tests and transvaginal ultrasounds. Once the follicles reach an optimal size, a final injection is given to trigger the eggs’ maturation.
The retrieval itself is a minor surgical procedure performed under light sedation. A thin needle, guided by ultrasound, is passed through the vaginal wall to aspirate the fluid and eggs from the mature follicles. Immediately following retrieval, the mature eggs are isolated and prepared for cryopreservation using vitrification. This method involves flash-freezing the eggs in a specialized cryoprotectant solution by plunging them into liquid nitrogen at -196°C, which prevents the formation of damaging ice crystals and allows the eggs to be stored indefinitely.