Euploidy rates within blastocysts obtained from differently sized cohorts and age groups approximate a binomial distribution.

Objective: To investigate whether the distribution of euploid blastocysts within cohorts can be predicted. Design: Retrospective observational study. Subjects: A total of 1,719 autologous egg retrieval cycles for in vitro fertilization from a single center that resulted in blastocysts biopsied for preimplantation genetic testing for aneuploidy. Exposure: Trophectoderm biopsy. Main Outcome Measures: Analysis of the statistical distribution structure of blastocyst euploidy within cohorts as functions of patient age and discrete cohort size. Results: A total of 9,385 blastocyst biopsy results were analyzed. Results were first categorized into the following genotype categories: euploid (61.1%); uniform whole chromosome aneuploid (32.9%); mosaic and/or segmental (3.3%); and inconclusive results (2.7%). Cohorts were then stratified by both age group (<30, 30-34, 35-37, 38-40, 41-42, and ≥43 years) and by cohort size from 1 to 10 blastocysts. Within age groups, the probability that a blastocyst was euploid progressively decreased with increasing age from 74.5% (<30 years) to 19.2% (≥43 years). Within each of the age groups, the probability for euploidy increased as the biopsied cohort size increased from 1 to 10 (odds ratio, 1.03 for each unit increase). Biopsies from younger age groups of <40 years showed predictably smooth increases in the number of e+/cohort as cohort size increased. Notably, the observed distribution of euploids/cohort showed no statistical differences from those expected from theoretical binomial calculations in 52 (91.2%) of 57 discrete subgroups identified by age and biopsied cohort size. Conclusion: The probability distribution structure of euploids within discrete cohort sizes is binomial within all age groups and nearly all cohort sizes. The probability distribution ranges identified represent a more accurate frame of reference that describes and predicts the number of euploid blastocysts most likely to be present within an individual cohort before biopsy compared with estimates from simple age group averages. These results offer new approaches for counseling and clinical decision-making.