High false‐positive non‐invasive prenatal screening results for sex chromosome abnormalities: Are maternal factors the culprit?

OBJECTIVE: To explore the impact of maternal sex chromosome aneuploidies (SCAs) and copy number variation (CNV) on false-positive results of non-invasive prenatal screening (NIPS) for predicting foetal SCAs. METHODS: In total, 22 844 pregnant women were recruited to undergo NIPS. Pregnant women with high-risk of SCAs underwent prenatal diagnosis and maternal copy number variation sequencing (CNV-seq). RESULTS: Among 117 women with high-risk of SCAs, 72 accepted prenatal diagnosis, 86 accepted maternal CNV-seq, and 21 had maternal sex chromosome abnormalities. The abnormality rate was significantly higher than women at low-risk of SCAs (24.42% vs 3.51%). Using a novel parameter cffDNA (ChrX)/cffDNA, when the ratio was greater than 2, all foetuses had normal karyotype, and 75.0% (6/8) had abnormal maternal chromosome X. If the ratio was less than or equal to 2, only 10% (4/40) of the mothers had chromosome X CNV alterations, while 33.3% (13/40) of their foetuses had sex chromosomes CNV abnormalities. CONCLUSIONS: Approximately 25% of pregnant women with SCAs predicted by NIPS had sex chromosome abnormalities as determined by CNV-seq. The ratio of cffDNA (ChrX)/cffDNA can tentatively distinguish the maternal or foetal origin of abnormal cell-free DNA. In a reanalysis of previous NIPS data, false-positive results caused by maternal CNV might be elucidated.