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Purpose: Chromosome band level is the primary quality indicator for G-banded metaphase chromosome analysis. Although current professional guidelines address the minimum necessary band level for constitutional studies, there is no study documenting the comparative performance of different band-level estimation methods., Methods: This study compared 5 band-level estimation methods (Stallard, Vancouver, Welborn, United Kingdom External Quality Assurance Scheme, and Ford) in a multicenter study in which 82 readers from 7 different clinical cytogenetics laboratories evaluated the same 10 karyotypes (5 from amniotic fluid and 5 from peripheral blood) by each method., Results: There was a 94% correlation between the five band-level estimation methods. The Welborn method yielded significantly lower scores for amniotic fluid karyotypes (P < 0.01) but not for peripheral blood karyotypes (P = 0.75). The distribution of scores obtained from different readers suggests a high level of subjectivity in chromosome band-level assessment. The variation in band-level estimation did not correlate with reader experience or study center, except for readers from one laboratory, for which the distribution of scores was significantly lower (P < 0.01)., Conclusion: The results from this study suggest that the consistent use of one method is more important than the actual method employed for monitoring karyotype quality.

Purpose: To evaluate the assumptions on which the American College of Medical Genetics (ACMG) Standards and Guidelines for detecting mosaicism in amniotic fluid cultures are based., Methods: Data from 653 cases of amniotic fluid mosaicism were collected from 26 laboratories. A chi-square goodness-of-fit test was used to compare the observed number of mosaic cases with the expected number based on binomial distribution theory., Results: Comparison of observed data from the in situ colony cases with the expected distribution of cases detected based on the binomial distribution did not reveal a significant difference (P = 0.525)., Conclusions: The empirical data fit the binomial distribution. Therefore, binomial theory can be used as an initial discussion point for determining whether ACMG Standards and Guidelines are adequate for detecting mosaicism.