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Background: Copy number variation sequencing (CNV-seq) is a powerful tool to discover structural genomic variation, but limitations associated with its retrospective study design and inadequate diversity of participants can be impractical for clinical application. Aim: This study aims to use CNV-seq to assess chromosomal aberrations in pregnant Vietnamese women. Materials & methods: A large-scale study was conducted on 3776 pregnant Vietnamese women with abnormal ultrasound findings. Results: Chromosomal aberrations were found in 448 (11.86%) women. Of these, 274 (7.26%) had chromosomal aneuploidies and 174 (4.61%) carried pathogenic/likely pathogenic CNVs. Correlations were established between chromosomal aberrations and various phenotypic markers. Conclusion: This comprehensive clinical study illuminates the pivotal role of CNV-seq in prenatal diagnosis for pregnancies featuring fetal ultrasound anomalies.

Objective: To demonstrate the prevalence of maternal mosaic monosomy X (MMXO) in a cohort of pregnant women in Vietnam., Methods: All 105,594 singleton pregnant women undergoing noninvasive prenatal screening (NIPS) between January 2019 and February 2021 in Vietnam were analyzed by measuring discordance between size- and count-based z-scores for chromosome X (ChrX) to identify suspected cases of MMXO and validated by fluorescence in situ hybridization (FISH) on maternal blood., Results: We identified 295 (0.279%) suspected MMXO cases. After FISH analysis, MMXO was confirmed in 125 cases (42.37%), revealing the MMXO prevalence of 0.118% (95% CI: 0.097-0.139%) in this cohort., Conclusion: We found a relatively high prevalence of MMXO in Vietnamese pregnant women and demonstrated a strong influence of MMXO on the ChrX z-score using a count-based method, resulting in false positives. The size-based method is not sensitive to MMXO and therefore achieves higher PPV.