All fresh miscarriage specimens were rinsed with saline solution for three times. Chorionic villi were separated from maternal decidua according to the standardized technology [9 (link)]. Samples where chorionic villi could not be clearly identified were excluded from this study. Genomic DNA was extracted from chorionic villi with the protocol of QIAamp DNA Mini Kit (Qiagen, Germany). Chromosomal abnormalities of POCs were detected by two CMA platforms in the current study, including CytoScan 750K array (Affymetrix, USA) and HumanCyto12-SNP array (Illumina, USA). SNP array experiments and molecular karyotype analysis for both platforms were performed as previously described [10 (link)]. Quantitative fluorescent polymerase chain reaction (QF-PCR) was subsequently performed to identify the percentage of maternal and foetal DNA if MCC was detected by CMA. Significant MCC referred to the proportion of MCC exceeding 30%. Samples with significant MCC were excluded from our study.
The two platforms could detect CNVs at an effective minimal resolution of 100 kb and regions of allelic homozygosity (ROHs) at a threshold of 5 Mb. Mosaicism for aneuploidies or CNVs ≥ 5 Mb was reported when the detection threshold of 30% was exceeded. CNVs were further classified as partial aneuploidy (CNVs ≥ 10 Mb, large CNVs) and microdeletions/microduplications (CNVs < 10 Mb, submicroscopic CNVs) based on their sizes. Pathogenicity of detected CNVs were evaluated according to the American College of Medical Genetics and Genomics (ACMG) and the Clinical Genome Resource (ClinGen) [11 (link)].