Performance of Cell-Free DNA Sequencing-Based Non-invasive Prenatal Testing: Our Experience on 36456 both Singleton and Multiple Pregnancies.

Abstract Background: To describe the clinical practice and performance of cell-free DNA sequencing-based noninvasive prenatal testing as a screening method for detecting trisomy 21, 18, and 13 (T21, T18, and T13, respectively), as well as sex chromosome aneuploidy (SCA), in a general Italian pregnancy population.Methods: The AMES-accredited laboratory offers noninvasive prenatal testing in maternal blood as a clinical screening test for foetal T21, T18, T13 and SCA. Samples were sequenced on a NextSeq 550 (Illumina) using the VeriSeq NIPT Solution v1 assay.Results: A retrospective analysis was performed on a cohort of 36456 consecutive maternal blood samples, including 35650 singleton pregnancies, 800 twin pregnancies, and 6 triplet pregnancies, which were tested between April 2017 and September 2019. The cohort included 46% elevated-risk and 54% low-risk patients. Genetic and/or clinical outcomes were available in 36000 cases (98.7%). In the overall cohort, 356 (1%) results were indicative of classic trisomy: 254 T21, 69 T18, and 33 T13. In addition, 145 results (0.4%) were indicative of SCA. Of the combined 501 screen-positive cases, 484 had confirmatory diagnostic testing results available: 99.2% (247/249) of T21 cases, 91.2% (62/68) of T18 cases, 84.4% (27/32) of T13 cases, and 86.7% (117/135) of SCA cases were confirmed. Follow-up data were available for 98.8% of the 35955 cases reported as unaffected by trisomy or SCA. No false negative cases were reported. The sensitivity of NIPT was 100.00% for T21 (95% Cl 98.47-100.0), T18 (95% Cl 94.17-100.0), T13 (95% Cl 87.54-100.0) and SCA (95% Cl 96.62-100.0). The specificities were 99.99% (95% Cl 99.98-100.0), 99.98% (95% Cl 99.96-100.0), 99.99% (95% Cl 99.97-100.0), and 99.95% (95% Cl 99.92-99.97) for T21, T18, T13, and SCA, respectively.Conclusion: This retrospective analysis of a large cohort of consecutive patients who had whole-genome sequencing-based NIPT for classic trisomies and SCA showed excellent detection rates and low false positive rates.