Novel method of real-time PCR-based screening for common fetal trisomies

The evolution of cell-free fetal DNA testing: expanded non-invasive prenatal testing and its effect on target populations

Purpose

To evaluate the clinical performance of expanded non-invasive prenatal testing (NIPT-plus) in screening for fetal chromosome aneuploidy and copy number variations (CNVs) among pregnant women with different risk factors to investigate how the target population of cell-free fetal DNA may change in NIPT-plus.

Methods

The clinical data, test results, confirmatory invasive testing outcomes, and follow-up results of 6,220 pregnant women who underwent NIPT-plus were re-viewed. The performance indicators of the positive predictive value (PPV), positive rate (PR), specificity, and sensitivity in screening for common trisomies, sex chromosomal abnormalities (SCAs), rare autosomal aneuploidies (RAAs), and CNVs were calculated. The PR or PPV of NIPT-plus for screening chromosome aneuploidy and CNVs in women of varying ages, risk factors, and clinical indications were determined.

Results

The PRs of common trisomies, SCAs, RAAs, and CNVs in NIPT-plus were 0.71, 0.45, 0.32, and 0.59%, respectively, with 100% sensitivity and specificities ranging from 99.69 to 99.87%. The PPVs were 80.95, 30.77, 13.33, and 44.12%, respectively. The high-risk group had higher PRs and PPVs for chromosome aneuploidy, with no significant difference in screening for CNVs. NIPT-plus showed greater PR for aneuploidy in the older age group than in the younger age group, with no significant differences in CNVs screening.

Conclusion

NIPT-plus was able to effectively screen for chromosome aneuploidy and CNVs. The performance of CNVs screening was not significantly different among different risk factors and age groups. The target population for NIPT-plus should include all pregnant women, not just those at high risk.

Focus on the frontier issue: progress in noninvasive prenatal screening for fetal trisomy from clinical perspectives

The discovery of cell-free fetal DNA (cffDNA) in maternal blood and the rapid development of massively parallel sequencing have revolutionized prenatal testing from invasive to noninvasive. Noninvasive prenatal screening (NIPS) based on cffDNA enables the detection of fetal trisomy through sequencing, comparison, and bioassays. Its accuracy is better than that of traditional screening methods, and it is the most advanced clinical application of high-throughput sequencing technologies. However, the existing sequencing methods are limited by high costs and complex sequencing procedures. These limitations restrict the availability of NIPS for pregnant women. Many amplification methods have been developed to overcome the limitations of sequencing methods. The rapid development of non-sequencing methods has not been accompanied by reviews to summarize them. In this review, we initially describe the detection principles for sequencing-based NIPS. We summarize the rapidly evolving amplification technologies, focusing on the need to reduce costs and simplify the procedures. To ensure that the testing systems are feasible and that the testing processes are reliable, we expand our vision to the clinic. We evaluate the clinical validity of NIPS in terms of sensitivity, specificity, and positive predictive value. Finally, we summarize the application guidelines and discuss the corresponding quality control methods for NIPS. In addition to cffDNA, extracellular vesicle DNA, RNA, protein/peptide, and fetal cells can also be detected as biomarkers of NIPS. With the development of prenatal testing, NIPS has become increasingly important. Notably, NIPS is a screening test instead of a diagnostic test. The testing methods and procedures used in the NIPS process require standardization.

Clinical application of expanded noninvasive prenatal testing for fetal chromosome abnormalities in a cohort of 39,580 pregnancies

The aim of this study was to determine the predictive value of expanded noninvasive prenatal testing (NIPT-plus) for fetal chromosome abnormalities in the second trimester (12-26 weeks). We conducted a retrospective cohort study of 39,580 pregnancies with NIPT-plus. Screening positive cases were diagnosed with karyotyping and single-nucleotide polymorphism array analysis (SNP array)/copy number variation sequencing (CNV-seq) with follow-up. The positive predictive values (PPVs) of trisomy 21, 18, and 13 (T21, T18, and T13), sex chromosome aneuploidies (SCAs), and microdeletion and microduplication syndromes (MMS) by NIPT-plus were recorded. We assessed the predictive value of NIPT-plus based on maternal age and conventional indications. Of 39,580 pregnancies with NIPT-plus, 511 (1.3%) had prenatal screening positive results of fetal chromosome abnormality, of which 87.7% (448/511) had invasive prenatal diagnosis. NIPT-plus performed better in predicting fetal SCAs and chromosome aneuploidies for pregnancies with advanced maternal age (AMA) than young maternal age (YMA). Besides, the PPVs of T21, T13, and chromosome aneuploidies showed an upward trend when comparison was based on maternal age in 5-year subintervals. The termination rates of 45,X, 47,XXX, 47,XXY, and 47,XYY were 100% (11/11), 20.0% (3/15), 91.7% (22/24), and 7.1% (1/14) with postnatal follow-up. Last but not least, the PPV for MMS is 41.7% (30/72), which may have a positive correlation between the size of CNVs. Pregnant women with screen-positive results for common trisomies (T13, T18, and T21) were more willing to conduct invasive prenatal diagnosis compared to those with positive results for SCAs or MMS. However, the current study demonstrated SCAs and MMS had the lowest PPV. This highlights the importance of confirmatory prenatal diagnosis in those patients and the potential impact on genetic counseling and informative decision-making.