Clinical validation of an abbreviated karyotype analysis protocol for fertility evaluation

Conventional G-banded karyotype is an essential tool for detecting chromosomal variants in patients undergoing fertility evaluation. In Australia, 15 cells are traditionally analysed or counted, to enhance detection of mosaic chromosomal variants. However, this protocol is not backed by clinical evidence. This study aims to assess the test performance of an abbreviated 5-cell karyotype analysis protocol in adult patients undergoing fertility evaluation. A retrospective review of 53,293 blood karyotype tests, performed between 2019 and 2023, was conducted on a patient cohort primarily referred by reproductive endocrinology specialists. There were 513 variants reported in this cohort. Low level mosaic variants, where the variant was observed in less than 40% of cells, were reported in 13 cases, or one in 4,100 patients. Due to reduced sensitivity for low level mosaic variants, a 5-cell protocol is estimated to have a test sensitivity of 97.3% and a negative predictive value of 99.97%. A decision-making flowchart is proposed and we show that additional chromosome analysis and/or counts would be triggered in fewer than one in 10 cases using a 5-cell protocol, whilst remaining appropriate for detecting clinically significant mosaicism. A 5-cell karyotype analysis protocol therefore maintains analytical and clinical validity in adult patients undergoing fertility-related blood karyotyping. Future research is recommended to validate these findings across laboratories and to explore their application to other clinical contexts.