![]() ![]() However, false negative NIPT results cannot be ignored in clinics and should be given more attention than false positive results because they are associated with more serious consequences and cause more stress to pregnant women and their families. However, this method does have limitations such as maternal malignancies and confined placental mosaicism (CPM) that lead to discordance between the fetal karyotype and NIPT results ( Wang et al., 2014 Bianchi et al., 2015), not all possible genetic disorders are detectable, some false positive or negative cases, as well as 3–5% non-reportable results due to low fetal fraction circulating free DNA (cfDNA) ( Liehr et al., 2017 Suzumori et al., 2019).Ī previous study reported the false negative rate of NIPT for T21 detection was only 0.09%, which is significantly lower than the false positive rate for the condition ( Hartwig et al., 2017). Non-invasive prenatal testing (NIPT) is widely used for detecting fetal chromosome trisomies 13, 18, and 21 (T13, T18, and T21) and sex chromosome aneuploidies with high sensitivity and specificity ( Porreco et al., 2014 Yu et al., 2017 Zhang et al., 2017). In conclusion, size selection can significantly enrich the fetal cfDNA fraction and decrease the false negative rate of NIPT, especially for CPM and twin pregnancies. Placental tissue analysis results for two cases indicated both had confined placental mosaicism (CPM), which was confirmed with size-selection NIPT. For one twin pregnancy with one T18 fetus, size selection improved the fetal cfDNA fraction to 23.10%, and successfully detected the T18 fetus in NIPT. For fetal cfDNA fraction, 100% cases had improvement after size-selection NIPT compared with the initial NIPT and retest results, and the fetal cfDNA fraction growth ratio ranged from 99 to 359%. Of eight retested cases, two (25%) had positive NIPT retest results, and five (62.5%) had positive size-selection NIPT results. Of the 81,601 pregnancies who underwent NIPT, nine false negative cases (0.01%) were found. ![]() Fetal placenta karyotypes were confirmed by CNVplex assays to analysis the reasons for false negative cases. In this study, nine false negative cases were retrospectively analyzed by NIPT retesting and E-gel based size-selection NIPT and the fetal cfDNA fraction in maternal total cfDNA was evaluated by calculating the proportion of reads from chromosome Y. Size selection of shorter cfDNA in total cfDNA could significantly increase the fetal fraction, but there are few reports of using this method to decrease the false negative rate for NIPT. 5Changzhou Maternity and Child Health Care Hospital Affiliated to Nanjing Medical University, Changzhou, ChinaĬirculating fetal cell-free DNA (cfDNA) is generally shorter than maternal cfDNA.4Zhejiang University Kunshan Biotechnology Laboratory, Zhejiang University Kunshan Innovation Institute, Kunshan, China.3State Key Laboratory of Bioelectronics, School of Biological Science and Medical Engineering, Southeast University, Nanjing, China.2Suzhou Municipal Hospital, Suzhou, China. ![]()
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