ABSTRACT
BACKGROUND: Non-invasive prenatal testing (NIPT) has been widely adopted as an approach for foetal aneuploidy screening. This study was to evaluate the performance of NIPT for foetal T21 detection in subgroups of pregnancies and the correlation between Z-score and discordant positive predictive values (PPVs). METHODS: We retrospectively reviewed the NIPT results among 22361 pregnancies undergoing combined second-trimester screening (cSTS) previously. Sixty-four cases with positive NIPT results for foetal T21 were validated by invasive prenatal diagnosis. RESULTS: In pregnancies with cSTS-T21 low-, intermediate-, and high-risk, the PPVs at NIPT were 14.3%, 64.3%, and 86.4%, respectively. Mean Z-scores of positive NIPT cases with cSTS-T21 high- and intermediate-risk were comparable, while were higher than that of cases with pre-test low-risk. Furthermore, PPVs for positive NIPT cases at 3 < Z < 5, 5 ≤ Z < 9, and Z ≥ 9 were 16.7%, 63.2%, and 100.0%, respectively. CONCLUSIONS: This study suggested that Z-score value of positive cases might be associated with discordant PPVs for T21 screening in subgroups of pregnancies.
Non-invasive prenatal testing has been offered as a primary screening option to high-risk or general pregnancy. However, the accuracy of non-invasive prenatal testing in patients with various pre-test risks remained unveiled. The current study revealed that the true positive probability for foetal trisomy 21 screening in pregnancies with prior high-risk was higher than that in pregnancies of intermediate-risk, and both of them were much higher than that of those with pre-test low-risk. The average of Z-score for chromosome 21 of positive non-invasive prenatal testing case in high-risk group was comparable with that of intermediate-risk group, while was higher than that of low-risk group. There was also an upward trend for the true positive probability of foetal trisomy 21 screening with the increase of Z-score. Our study revealed that pre-test risk and Z-score for chromosome 21 were helpful for accurately interpreting the reliability of positive results for foetal trisomy 21.
