[Confirmation and analysis of 2 398 positive results of cell-free fetal DNA]

Objective: To explore the clinical application value and accuracy of cell-free fetal DNA (cff-DNA) technique in prenatal screening. Methods: The results of quantitative fluorescent PCR (QF-PCR) and karyotype of amniotic fluid cells were analyzed retrospectively in 2 398 monocyesis pregnant women who had been amniocentesis at the First Affiliated Hospital of Zhengzhou University from May 2013 to December 2019, and the results of 359 cases who had been examined by single-nucleotide polymorphism array (SNP array). Results: Cff-DNA test of 2, 398 cases indicated 987 cases of trisomy 21, 351 cases of trisomy 18, 135 cases of trisomy 13, 566 cases of sex chromosome abnormality, and 359 cases of other chromosome abnormality. Chromosome karyotype analysis detected 826 cases of trisomy 21, 213 cases of trisomy 18, 17 cases of trisomy 13, 221 cases of sex chromosome abnormality, and 26 cases of other chromosome abnormality. The detection rate were 83.69% (826/987), 60.68% (213/351), 12.59% (17/135), 39.04% (221/566) and 7.24% (26/359), respectively. QF-PCR detected 1 046 cases of trisomy and 188 cases of sex chromosomes abnormality, and the detection rate was 99.05% (1 046/1 056) and 85.07% (188/221), respectively. Compared with the abnormal number detected by chromosome karyotype analysis, 10 cases of trisomeric chimerism and 24 cases of sex chromosome were missed by QF-PCR. Among the 359 other chromosomal abnormalities detected by SNP array, 64 cases were consistent with the results of cff-DNA, and the detection rate was 17.83% (64/359), which was 10.59% higher than the karyotype result. Conclusions: Karyotype analysis is the gold standard for diagnosing chromosomal abnormalities. QF-PCR could diagnose common chromosome aneuploidy rapidly and accurately, and it could be used as an auxiliary detection technique for karyotype analysis. The incidence of sex chromosome chimerism is high, so missed diagnosis should be warned. SNP array could be given priority to verify chromosome microdeletion or microduplication detected by cff-DNA.