[Analysis to the failure rate and causes of noninvasive prenatal testing based on high-throughput sequencing]

To analyze the cause and pregnancy outcome for non-reportable cell-free DNA (cfDNA) results during non-invasive prenatal testing (NIPT).

cfDNA was extracted from maternal plasma from 5898 singleton pregnancies at 12 to 22 gestational weeks and underwent NIPT with strict quality control standards. For those with sub-standard results, redraw or invasive prenatal procedures were recommended.

Among the 5898 cases, 32 have failed for the initial NIPT, including 17 cases with substandard cffDNA%, 10 cases with data fluctuation after twice library constructing and sequencing, and 5 cases with unidentifiable sex chromosome abnormalities. For these 32 cases, 2 directly underwent amniocentesis, and karyotyping analysis showed both were normal. Six of the 30 redrawn cases finally turned out to be nonreportable. The final nonreportable rate was therefore 0.1% (8/5898). Of the redrawn cases, 1 trisomy 21, 1 trisomy 18 and 1 trisomy 13 high risk-cases were identified, which were all confirmed to be false positive. Among the 6 nonreportable cases, 2 women underwent invasive prenatal testing, and 1 was found to have a normal fetal karyotype, while another was found to have an abnormal karyotype of mos45,X[32]/46,XY[18]. The other 4 nonreportable cases who did not accept invasive prenatal testing have all reported normal child development at follow-up.

The main reason for nonreportable NIPT results was low cffDNA%. The high success rate of the redrawn cases has effectively increased the overall NIPT success rate and reduced the number of the cases necessitating invasive prenatal diagnosis. The initially nonreportable women may consider retesting after careful counseling with informed consent.