Abstract: 【Abstract】 Objective To discuss the application value of retest in non-invasive prenatal test（NIPT）for pregnant women. Methods From October 2017 to December 2018, the appropriate population who was treated in the Prenatal Diagnosis Center of The Beijing Haidian Maternal and Child Health Hospital was screened by NIPT. The blood collection，plasma separation by centrifugation, extraction of cf DNA, library construction, analysis of quality control, massively parallel sequencing (MPS), noninvasive prenatal fetal chromosome aneuploidy analysis and other steps were performed at 12~ 27+6 weeks of gestation for target diseases (trisomies 21, 18 and 13). Retest methods were redrawing blood and rebuilding the DNA library to avoid failed detection and Z score grey area (the target chromosome Zscore was between 3 and 4). Pregnant women with high risk of fetal aneuploidy by NIPT were performed interventional prenatal diagnosis. The causes and results of retest were analyzed. Results A total of 6 110 cases with NIPT were included, 315 cases (5.16%, 315/6 110) were performed retest, of which 56 cases (0.92%, 56/6110) were redrew the blood, and that of the other 259 cases were rebuilt the DNA library (4.4%，259/6110). The reasons were analyzed that 155 cases were (2.53%, 155/6 110) failed in detection, 160 cases (2.62%, 160/6110) were Z score grey area. The 155 cases of test failure were as follows: 16 cases were unqualified samples (2 cases of blood clotting, 3 cases of expired blood sample and 11 cases of unsuitable storage temperature, and no high-risk case was found in the redrawing test); there were 67 cases of unqualified DNA library quality control (5 cases of abnormal peaks in the DNA library, 62 cases of low
library concentration, among which no high-risk case was found in the reconstruction of the library). There were 72 cases of failed sequencing data quality control, including GC content bias in 43 cases (among no high-risk case was found in the reconstruction of the library), low fetal concentrations in 21 cases (fetal concentrations were still low in 3 cases after redrawing, and 1 case was high-risk in the remaining 18 cases), multiple chromosomal abnormalities in 7 cases (1 case was high-risk after redrawing), insufficient sequencing data in 1 case (low risk case was found in the reconstruction of the DNA library). 160 cases of
Z score gray area were as follows: 34 cases were identified as high-risk after rebuilding DNA library in 148 cases; 12 pregnant women with Z score gray area after rebuilding DNA library were performed redrawing, and 5 cases were identified as high-risk. A total of 121 cases (75.6%, 121/160) were low risk by repeated testing. 41 cases with high risk of target chromosome were performed interventional prenatal diagnosis to confirm 26 cases were abnormal chromosome. Conclusions NIPT detection involves many quality control points, and necessary retest plays an important role in the quality control of NIPT experiment.
Repeated detection in the Z-score gray area can reduce the fals e positive rate of NIPT.
2019, Vol. 7 
