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In the TRIDENT-2 study, all pregnant women in the Netherlands are offered genome-wide non-invasive prenatal testing (GW-NIPT) with a choice of receiving either full screening or screening solely for common trisomies. Previous data showed that GW-NIPT can reliably detect common trisomies in the general obstetric population and that this test can also detect other chromosomal abnormalities (additional findings). However, evidence regarding the clinical impact of screening for additional findings is lacking. Therefore, we present follow-up results of the TRIDENT-2 study to determine this clinical impact based on the laboratory and perinatal outcomes of cases with additional findings. Between April 2017 and April 2019, additional findings were detected in 402/110,739 pregnancies (0.36%). For 358 cases, the origin was proven to be either fetal (n = 79; 22.1%), (assumed) confined placental mosaicism (CPM) (n = 189; 52.8%), or maternal (n = 90; 25.1%). For the remaining 44 (10.9%), the origin of the aberration could not be determined. Most fetal chromosomal aberrations were pathogenic and associated with severe clinical phenotypes (61/79; 77.2%). For CPM cases, occurrence of pre-eclampsia (8.5% [16/189] vs 0.5% [754/159,924]; RR 18.5), and birth weight <2.3rd percentile (13.6% [24/177] vs 2.5% [3,892/155,491]; RR 5.5) were significantly increased compared to the general obstetric population. Of the 90 maternal findings, 12 (13.3%) were malignancies and 32 (35.6%) (mosaic) pathogenic copy number variants, mostly associated with mild or no clinical phenotypes. Data from this large cohort study provide crucial information for deciding if and how to implement GW-NIPT in screening programs. Additionally, these data can inform the challenging interpretation, counseling, and follow-up of additional findings., Competing Interests: Declaration of interests E.A.S. was one of the applicants of the ZonMW grant and is a member of the GenQA advisory board (unpaid) and the associate editor of Extracellular Vesicles and Circulating Nucleic Acids. D.V.O. is a member of the project group NIPT additional findings and Project group NIPT Laboratories of the National Institute for Public Health & Environment (RIVM) – Center for Population Screening (CvB). L.H. was one of the applicants of the ZonMW grant. M.N.B. is a member of the project group NIPT additional findings, of the RIVM-CvB (unpaid). C.J.B. is a member of the project group NIPT additional findings, of the RIVM-CvB (unpaid). M.J.P. is a member of the Project group NIPT Quality, and Project group NIPT additional findings, all of the RIVM-CvB (unpaid). M.V.E.M. is a member of the Program Committee Prenatal Screening, Project group NIPT Quality, and Project group NIPT Laboratories, all of the RIVM-CvB (unpaid). Part of the ZonMW grant was paid to his institution for TRIDENT-2 bio-informatic research. R.-J.H.G. was one of the applicants of the ZonMW grant, and he is a member of the Program Committee Prenatal Screening, Project group NIPT Quality, and Project group NIPT additional findings, all of the RIVM-CvB (unpaid)., (Copyright © 2022 The Authors. Published by Elsevier Inc. All rights reserved.)

The Netherlands launched a nationwide implementation study on non-invasive prenatal testing (NIPT) as a first-tier test offered to all pregnant women. This started on April 1, 2017 as the TRIDENT-2 study, licensed by the Dutch Ministry of Health. In the first year, NIPT was performed in 73,239 pregnancies (42% of all pregnancies), 7,239 (4%) chose first-trimester combined testing, and 54% did not participate. The number of trisomies 21 (239, 0.33%), 18 (49, 0.07%), and 13 (55, 0.08%) found in this study is comparable to earlier studies, but the Positive Predictive Values (PPV)-96% for trisomy 21, 98% for trisomy 18, and 53% for trisomy 13-were higher than expected. Findings other than trisomy 21, 18, or 13 were reported on request of the pregnant women; 78% of women chose to have these reported. The number of additional findings was 207 (0.36%); these included other trisomies (101, 0.18%, PPV 6%, many of the remaining 94% of cases are likely confined placental mosaics and possibly clinically significant), structural chromosomal aberrations (95, 0.16%, PPV 32%,) and complex abnormal profiles indicative of maternal malignancies (11, 0.02%, PPV 64%). The implementation of genome-wide NIPT is under debate because the benefits of detecting other fetal chromosomal aberrations must be balanced against the risks of discordant positives, parental anxiety, and a potential increase in (invasive) diagnostic procedures. Our first-year data, including clinical data and laboratory follow-up data, will fuel this debate. Furthermore, we describe how NIPT can successfully be embedded into a national screening program with a single chain for prenatal care including counseling, testing, and follow-up., (Copyright © 2019 American Society of Human Genetics. Published by Elsevier Inc. All rights reserved.)