In vitro fertilization (IVF) often results in more viable embryos than can be safely transferred in a single cycle. Embryo cryopreservation, commonly known as freezing, safely stores these surplus fertilized eggs for future use. This technique allows patients to pursue subsequent pregnancies without repeating the ovarian stimulation and egg retrieval phases of IVF. Deciding on the appropriate number of embryos to freeze is a highly complex and individualized decision, balancing biological factors, statistical probabilities, and personal family goals.
Personalized Factors Determining the Target
The initial target number of embryos a medical professional recommends freezing is rooted deeply in the patient’s unique biological profile and stated family aspirations. Maternal age at the time of egg retrieval is the single most important variable influencing this prediction, as it directly correlates with the genetic health and viability of the resulting embryos. For a patient aged 35 or older, the recommendation for the number of embryos to bank will be higher compared to a younger patient, primarily to offset the increased likelihood of chromosomal abnormalities.
A patient’s desired family size is another significant driver of the target number, as the strategy for banking one child differs significantly from planning for two or three children. Clinicians use the goal of achieving one live birth per child to calculate the total number of quality embryos needed, allowing for potential failed transfers or miscarriages. Planning for multiple children naturally increases the number of embryos advised for cryopreservation to ensure sufficient options for the future.
The ovarian reserve, assessed through markers like Anti-Müllerian Hormone (AMH) levels and Antral Follicle Count (AFC), offers insight into the likely number of eggs that can be retrieved and, consequently, the number of embryos that may be created in a cycle. A low ovarian reserve may necessitate multiple IVF cycles to reach a desired freezing target. Furthermore, a history of poor fertilization or implantation from previous IVF cycles may lead to a higher target number, acting as a buffer against future unexpected outcomes.
Assessing Embryo Quality Before Freezing
The sheer quantity of cryopreserved embryos is less important than their inherent quality, which is determined through a two-part assessment process before freezing is finalized. Embryologists use a standardized morphology-based embryo grading system, most commonly on Day 5 or Day 6 of development when the embryo reaches the blastocyst stage. This grading system evaluates three main characteristics: the expansion level of the blastocyst, the quality of the Inner Cell Mass (ICM) that forms the fetus, and the quality of the Trophectoderm (TE) that will form the placenta.
A high-grade blastocyst, such as a 5AA, is considered to have a greater structural potential for implantation and survival after thawing compared to a lower-grade embryo. However, this morphological assessment is subjective and does not provide genetic information. Preimplantation Genetic Testing for Aneuploidy (PGT-A) is an optional but powerful tool that assesses the chromosome count of the embryo.
An embryo confirmed as euploid, meaning it has a normal number of chromosomes, has a significantly higher chance of resulting in a live birth. Testing for euploidy drastically refines the freezing decision, as the number of embryos required to achieve a pregnancy drops considerably once genetic normalcy is confirmed. In many cases, a single euploid embryo may offer a chance of live birth that is comparable to transferring multiple untested, but morphologically high-grade, embryos.
Statistical Probability of Live Birth Per Embryo
The ultimate goal of banking is to achieve a high cumulative success rate, which is the chance of live birth after using all the embryos created from a single egg retrieval cycle. Current statistical models show that the live birth rate from a single Frozen Embryo Transfer (FET) is highly variable, but often falls in the range of 40% to 50% per transfer for high-quality embryos. This rate depends on the patient’s age and whether PGT-A was performed.
Clinicians use these statistics to calculate a target number of embryos needed to reach a high-confidence level, often aiming for an 80% to 90% cumulative chance of achieving the desired family size. For instance, if the live birth rate per transfer is assumed to be 50%, a patient would statistically need at least two genetically normal embryos banked per desired child to have an approximately 75% cumulative chance of one live birth. Banking additional embryos beyond the minimum is a critical strategy to manage the risk of multiple failed transfers.
For patients who opt for PGT-A, the statistics become more precise; research suggests that banking three euploid blastocysts provides a cumulative chance of live birth exceeding 90%. Conversely, in cases where PGT-A is not used, a higher number of embryos must be frozen to account for the unknown proportion that may be aneuploid. This statistical modeling allows the fertility team to provide a personalized, data-driven recommendation for the number of embryos to bank.
Logistical and Financial Considerations
Beyond the medical and statistical calculations, patients must also consider the practical aspects of long-term embryo storage. Embryos are stored indefinitely in liquid nitrogen tanks, but this requires paying annual cryopreservation fees. These yearly storage costs typically range from $350 to $1,500, and these fees can accumulate significantly over many years.
Some clinics or long-term storage facilities offer reduced rates for multi-year contracts, which can help mitigate the long-term financial burden. The decision to freeze a large number of embryos must therefore be weighed against the potential for decades of recurring storage expenses.
Patients must also establish legal agreements regarding the final disposition of any unused embryos, addressing what happens to them in the event of divorce, death, or when family building is complete. These legal and ethical considerations are a significant part of the overall decision, as storing a large cohort of embryos can carry an emotional and moral weight that needs to be resolved upfront.