Non-invasive prenatal testing for the detection of trisomies 21, 18, and 13 in pregnant women with various clinical indications: A multicenter observational study of 1,854,148 women in China.

Objective: This study aimed to evaluate the performance of noninvasive prenatal testing (NIPT) for detecting three common trisomies (T21, T18, and T13) in pregnant women with diverse clinical indications.

Methods: Frequencies of NIPT, of high chance of having one of the three trisomies, and of confirmed trisomies were determined for women with each of seven clinical indications in a national cross-sectional survey of approximately 300 prenatal diagnosis centers. Data were collected for the period from October 1, 2016 to September 30, 2018 using the Prenatal Diagnosis Technology Management On-line Information System. The performance of NIPT for detecting the three trisomies in pregnant women with different clinical indications was assessed in terms of sensitivity, specificity, positive predictive value (PPV), negative predictive value, and the corresponding 95% confidence intervals.

Results: A total of 5766 true positive cases for T21, T18, and T13 were detected among 1,854,148 samples, giving an overall detection rate of 0.31% (95% CI: 0.30%-0.32%). Most positive cases were associated with "NT thickening" (1.18%) and "advanced maternal age" (0.51%). The detection sensitivities of NIPT were 99.60% for T21, 99.14% for T18, and 100% for T13, while the corresponding specificities were 99.90%, 99.94%, and 99.95%. The corresponding PPVs were 69.77%, 47.24%, and 22.36%. NIPT showed high sensitivity and specificity, regardless of clinical indication. In contrast, PPV for three trisomies varied widely between 9.09% and 66.46% depending on the clinical indication. Across seven clinical indications, PPV ranged from 50.62% to 73.09% for T21, 20.00%-58.33% for T18, and 4.17%-47.37% for T13. The highest PPVs were 73.09% for T21 in pregnancies involving "advanced maternal age", 58.33% for T18 in pregnancies with "NT thickening", and 47.37% for T13 in pregnancies with "NT thickening".

Conclusions: NIPT shows high sensitivity and specificity for detecting T21, T18, and T13 in pregnant women with different clinical indications. However, PPV depends strongly on clinical indication, highlighting the need to strengthen education and genetic counseling about prenatal screening.