Glossary · Definition · v2026.3
Embryo Cohort in IVF
The embryo cohort is the group of embryos produced from a single egg retrieval cycle. Cohort size determines the number of available transfer attempts and is the denominator in cumulative live birth rate calculations.
Why Cohort Size Matters
A larger embryo cohort provides more transfer opportunities, increasing cumulative probability of live birth. If a retrieval produces 3 euploid embryos, each transfer attempt adds to the cumulative probability. Cohort size is primarily determined by the number of eggs retrieved, fertilization rate, and blastocyst conversion rate, all of which are constrained by age and biology.
Biological Constraints
Attrition reduces the cohort at each stage: not all eggs will fertilize, not all fertilized eggs will reach blastocyst, and not all blastocysts will test euploid. Planning at the cohort level rather than the single-transfer level provides more realistic expectations for IVF outcomes.
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This content defines terminology for educational orientation. It does not constitute medical advice.
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