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Abstract To explore the value of non-invasive prenatal (NIPT) of fetal free DNA in peripheral blood of pregnant women for diagnosing fetal chromosome abnormality, and to analyze the causes of false positive of fetal chromosome abnormality. Methods: From January 2017 to June 2019, 10236 pregnant women with single live fetus who had undergone NIPT were selected in this study, and the chromosome karyotype of fetus with abnormal NIPT results was analyzed by amniocentesis to evaluate the diagnostic value of NIPT for chromosome abnormality. The samples of placental tissue and maternal blood of the women with NIPT false positive and normal amniocentesis karyotype analysis who chosen continually pregnancy until to delivery were collected for DNA sequencing analysis. Results: A total of 111 cases in 10236 pregnant women were detected chromosomal abnormalities by NIPT, which’s detection rate was 1.08%. Among them, there were 34 (30.6%) cases with 21- trisomy, 20 (18.0%) cases with 18- trisomy, 17 (15.3%) cases with 13- trisomy, 35 (31.5%) cases with sex chromosome, and 5 (4.5%) cases with other abnormal chromosomes. In the fetus with NIPT abnormalities after amniocentesis performed, there were 92 (92/111, 82.9%) cases with confirmed abnormal chromosomes and 19 (19/111, 17.12%) cases with normal chromosomes, and the overall false positive rate was 0.19% (19/10236). The coincidence rates of NIPT for screening 21-trisomy, 18- trisomy, 13- trisomy, and sex chromosome were 94.1%, 90.0%, 76.5%, and 74.3%, respectively. Among the 19 cases with false positive of NIPT, the detective results of placenta tissue of 12 cases had the same results as their NIPT, the detective results of maternal blood of 5 cases had the same results as their NIPT, and 2 cases could not determine the false positive reason of NIPT. Conclusion: NIPT has high value for prenatal screening fetal chromosomal abnormalities with certain false positive rate. The abnormal free DNA of placenta tissue enters the maternal blood and the abnormal maternal free DNA are the main causes of NIPT false positive.
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