Non‐invasive cell‐free DNA prenatal screening for trisomy 21 as part of primary screening strategy in twin pregnancies

Abstract

AbstractObjectivesThe performance of non‐invasive prenatal screening using cell‐free DNA testing in maternal blood in twin pregnancies is still under‐evaluated, while serum marker‐based strategies yield poor results. This study aims at assessing the performance of non‐invasive prenatal screening for trisomy 21 in twin pregnancies as a first‐tier test. The secondary objectives were to assess the failure rate and associated factors.MethodsThis retrospective cohort study included twin pregnancies for which non‐invasive prenatal screening using cell‐free DNA was performed as the primary screening strategy between May 2017 and October 2019. We used the NIPT VeriSeq® test for in vitro diagnosis and set a fetal fraction cut‐off of 4% for monochorionic pregnancies and 8% for dichorionic ones. Clinical data and pregnancy outcome was collected from either physicians or midwives through a questionnaire or were retrieved directly on site. We calculated the performance of non‐invasive cell free DNA screening for trisomy 21 and analyzed failure rate and factors.ResultsWe included 2577 multiple pregnancies among which 1885 (84.8%) were retained after excluding vanishing twins and pregnancies without follow‐up. Overall, there were six confirmed trisomy 21 cases (0.32%). For trisomy 21, sensitivity was 100% (95% CI, 61‐100%) and the false‐positive rate 0.2% (95% CI, 0.07‐0.6%). The primary failure rate was 4.6% with 4% due to insufficient fetal fraction. After a new blood draw (59.8% of failed cases), failure rate was only 1.5%. Body mass index and chorionicity were significantly correlated with the risk of failure.ConclusionThis study adds further evidence on the high performance of NIPS in twins, as part of the primary screening strategy for trisomy 21, at an extremely low false‐positive rate.This article is protected by copyright. All rights reserved.