When you start exploring frozen donor egg cycles, one of the first practical questions is: how many eggs do I actually need? Egg banks sell frozen eggs in cohorts — typically packages of a defined number of eggs from a single donor. The sizes vary: some banks offer cohorts of 4, 6, 8, or more eggs. The price per cohort varies. And the probability of achieving a live birth varies considerably depending on how many eggs you start with.

Understanding the relationship between cohort size and success probability is one of the most practically important things an intended parent can do before purchasing a donor egg cohort — and it's an area where the numbers are frequently misunderstood. This guide breaks it down clearly.

The Attrition Pipeline: From Eggs to Baby

The journey from frozen donor eggs to a live birth involves several stages, each of which involves natural attrition — a proportion of eggs or embryos that do not progress to the next stage. Understanding this pipeline is essential for making sense of cohort size recommendations.

💡 A useful rule of thumb: on average, approximately 1 in 3 to 1 in 5 mature frozen donor eggs will result in a live birth. This varies with egg quality, laboratory expertise, sperm quality, and recipient uterine health. Starting with more eggs increases your cumulative probability of success — but even a small cohort of high-quality eggs from an experienced bank can be sufficient for many intended parents.

• Stage 1 — Post-thaw survival: After thawing, not all frozen eggs survive. At high-quality vitrification laboratories, survival rates of 80–90% are standard. From a cohort of 8 eggs, expect approximately 6–7 to survive thaw at this rate.
• Stage 2 — Fertilisation: Surviving eggs are fertilised using ICSI (intracytoplasmic sperm injection). Fertilisation rates for donor eggs are typically 70–80%. From 7 surviving eggs, expect 5–6 to fertilise.
• Stage 3 — Blastocyst development: Not all fertilised eggs reach the blastocyst stage by day 5 or 6. Blastocyst development rates are typically 40–60% of fertilised eggs. From 5–6 fertilised eggs, expect 2–4 blastocysts.
• Stage 4 — PGT-A (if tested): If preimplantation genetic testing is performed, approximately 50–60% of blastocysts from donor egg cycles are chromosomally normal (euploid). From 3 blastocysts, expect 1–2 euploid embryos.
• Stage 5 — Implantation and live birth: Euploid embryos transferred in a prepared uterine cycle have implantation rates of approximately 60–70% per transfer at specialist centres. From 1–2 euploid embryos, cumulative live birth probability is meaningful — but not certain from a single transfer.

What the Research Shows About Cohort Size and Success

A 2025 study in BMC Pregnancy and Childbirth modelling cumulative live birth rates in frozen donor egg cycles found that cohorts of 6 or more mature eggs produced significantly higher cumulative live birth rates than cohorts of 4 or fewer — particularly when PGT-A was incorporated into the cycle. The study found that the cumulative live birth rate from a cohort of 8 mature eggs approached 70–75% across multiple transfers, compared to approximately 45–50% from a cohort of 4 eggs.

A 2022 review in Fertility and Sterility examining outcomes from frozen oocyte donation cycles found that the number of mature oocytes surviving thaw was the single strongest modifiable predictor of cumulative live birth rate — reinforcing that starting cohort size, combined with post-thaw survival rates, is the most actionable lever intended parents can influence through bank selection.

Standard Cohort Sizes and What They Mean in Practice

4-egg cohort: The smallest commonly offered package. At standard attrition rates, a 4-egg cohort will typically produce 1–2 blastocysts with 0–1 euploid embryos after PGT-A. This cohort size carries a meaningful probability of producing no transferable embryo, particularly if any stage of the pipeline underperforms. It may be appropriate for intended parents with strong uterine health who plan to transfer without PGT-A, or as an additional cohort on top of an existing embryo bank.

6-egg cohort: The most common starting point for intended parents pursuing a first frozen donor egg cycle. At standard attrition rates, a 6-egg cohort typically produces 2–3 blastocysts with 1–2 euploid embryos. This gives most intended parents at least one transferable embryo and a reasonable cumulative probability of live birth across 1–2 transfers.

8-egg cohort: The recommended starting point for intended parents who want higher confidence of having multiple transferable embryos — including backup embryos if a first transfer fails or if they want to build a family of more than one child. An 8-egg cohort typically produces 3–4 blastocysts with 1–3 euploid embryos, providing meaningful cumulative success probability and the option of embryo banking for a sibling cycle.

Larger cohorts (10+ eggs): For intended parents with a history of implantation failure, poor embryo development, or significant male factor infertility, a larger starting cohort provides greater resilience at each stage of the pipeline. Multiple cohorts from the same donor can sometimes be arranged, which also allows intended parents to bank embryos systematically.

Factors That Affect How Many Eggs You Actually Need

The "right" cohort size is not universal — it depends on your specific clinical picture. Key variables include:

• Sperm quality: If the intended father's or donor sperm has abnormal morphology, poor motility, or elevated DNA fragmentation, fertilisation rates and blastocyst development rates may be lower than average — meaning more eggs are needed to achieve the same number of transferable embryos.
• Whether you're doing PGT-A: If you plan to test embryos for chromosomal abnormalities before transfer, expect the pipeline to narrow further at the testing stage. PGT-A is highly advisable for maximising transfer success rates but does reduce the number of transferable embryos from any given cohort.
• Uterine health: If there are known uterine factors — thin lining, adenomyosis, Asherman's syndrome — implantation rates per transfer will be lower, and more attempts (and therefore more embryos) may be needed.
• Your family building goals: If you hope to have two children through donor egg IVF, banking sufficient embryos from a single donor is a meaningful consideration — both for practical reasons (same donor is genetically related to both children) and for logistical ones (donor availability cannot be guaranteed in future cycles).

Why Egg Quality Matters As Much As Quantity

Cohort size is one side of the equation — egg quality is the other. A cohort of 8 eggs from a donor with strong AMH, a good antral follicle count, a clean genetic screening history, and excellent retrieval conditions will perform very differently from a cohort of 8 eggs that spent months in suboptimal storage conditions at a laboratory with limited vitrification expertise.

Asian Egg Bank's eggs are vitrified by Hanabusa IVF's specialist laboratory in San Diego — a facility with over 10 years of dedicated vitrification expertise. Every cohort offered through Asian Egg Bank comes with documented post-thaw survival data and is backed by rigorous donor screening — including extended genetic carrier screening, ovarian reserve testing to confirm adequate response potential, and comprehensive health assessment.

The combination of sufficient cohort size and high-quality vitrification is what consistently produces the cumulative success rates that make donor egg IVF worthwhile. Our team can help you think through cohort size in the context of your specific clinical situation — without pressuring you toward a larger purchase than your situation warrants.

Frequently Asked Questions

Can I buy additional eggs from the same donor later if my first cohort is not enough? This depends on whether additional cohorts from your chosen donor are available. Some donors have multiple cohorts banked; others do not. If sibling embryos or a second cycle from the same donor matters to you, discussing cohort reservation at the outset is worth doing.

Should I do PGT-A on a donor egg cycle? PGT-A is not universally required but is widely recommended — it identifies chromosomally normal embryos before transfer, reducing the risk of failed implantation and miscarriage. Your fertility clinic will advise based on your age, reproductive history, and sperm quality. Note that PGT-A reduces the number of transferable embryos from any cohort, which is a relevant consideration for cohort size planning.

What if all the eggs in my cohort fail to fertilise? This is very rare with high-quality vitrified donor eggs and ICSI, but it can occur — most commonly when there is a sperm-egg interaction issue or an undiagnosed severe sperm factor. Asian Egg Bank's team works with your clinic to assess what happened and to determine the best next step, which may involve additional eggs, a different fertilisation approach, or both.

Is a larger cohort always better? Not necessarily — for intended parents with excellent uterine health, good sperm quality, and a plan to transfer without PGT-A, a 6-egg cohort may be entirely sufficient. The goal is to match cohort size to your specific pipeline risk, not to maximise eggs regardless of cost.

Does Asian Egg Bank offer different cohort sizes? Yes. Our team will discuss available cohort sizes for specific donors at the time of your consultation. Cohort size varies by what has been banked from each donor's retrieval cycle, and our coordinators will be transparent about what is available.

Start With the Right Numbers — and the Right Partner

Understanding the attrition pipeline from frozen eggs to live birth is the foundation of making a well-informed cohort size decision. Asian Egg Bank's team is here to help you think through that decision honestly — with the goal of giving you the best possible chance of success, not the largest possible cohort sale. Explore our donor database and speak with our coordinators today.