Selective growth of mosaic cells in chromosomal analysis of chorionic villi by conventional karyotyping

The major cause of first-trimester pregnancy loss is chromosomal abnormality, which could be detected by many methods. Conventional karyotyping based on chorionic villi (CV) culture is frequently used but may have limitations due to culture failure and selective growth of cells. In this study, we aimed to investigate the degree of mosaicism present in villi by a combination of three different methods, namely conventional karyotyping following culture, multiplex ligation-dependent probe amplification (MLPA) and fluorescence in situ hybridization (FISH), with a view to exploring the incidence of selective growth of mosaic CV cells during the process of culture for conventional karyotyping. CV samples were obtained from 207 patients with early spontaneous miscarriage (ESM). There were 56 (56/207, 27.1%) samples with mosaic chromosome detected by FISH based on four or five types of probes in this study. The incidence of selective growth of mosaic cells during the process of conventional karyotyping was 6.0% (11/183). In addition, we found that mosaic cell lines as low as 2% could grow and completely dominate the outcome of karyotyping results. The selective growth of a particular cell line during culture, whether euploidy or aneuploidy, could supress the diagnosis of mosaicism.