Tracking and Analysis of Initial Noninvasive Prenatal Testing Failure: A Retrospective Study

Abstract Background : To classify and analyze the risk factors associated with initial noninvasive prenatal testing (NIPT) failure in the context of pregnancy outcomes. Methods : From May 2019 to April 2022, 30039 singleton pregnant women were enrolled in the NIPT, for whom initial failure samples were analyzed and followed up. The initial and final test failure rates were determined. The risk factors of initial test failure were classified as follows: the repeat test success rate and positive predictive values (PPVs) of “z-score in gray area” samples were analyzed; the difference between cases with initial “low fetal fraction (FF)” result and initial “low risk” result, the key factors for success in the second test, and the effect of experimental conditions on the detection rate of low FF samples were assessed; the final NIPT results and pregnancy outcomes of samples with “quality control (QC) failure” were followed up and evaluated. Results : The total initial failure rate and final failure rate were 2.7% and 0.12% respectively. 99.04% of “z-score in gray area” samples obtained results after repeated test. Of the 22 cases with abnormal or no results, only 15 cases conducted prenatal diagnosis none of which revealed abnormalities with clear clinical significance. Body mass index (BMI), gestational age, library concentration, and fetal sex were considered risk factors for initial low FF results, but were not critical for the success of the second test, or even for initial fetal concentration. The incidence of low FF samples was more frequent with G-type blood collection tubes than with K-type tubes. A total of 99.22% of the QC failure samples obtained interpretable results after resampling or library reconstruction, and all were at low risk. Conclusions : NIPT has a low final failure rate, but the initial failure rate warrants attention. The PPV of the initial gray area samples was low. Maternal BMI, gestational age, library concentration, fetal sex, and type of blood collection tube may be risk factors for “low FF”.