LAUSR

INTRODUCTION Since 2021 first-trimester anatomical screening (FTAS) is offered in the Netherlands alongside genome-wide-cell-free DNA. Previously, only second-trimester anatomical screening (STAS) was offered. This study identifies structural abnormalities amenable to first-trimester diagnosis detected at/after STAS in the period following cfDNA implementation and preceding FTAS introduction. METHODS This retrospective-cohort includes 547 fetuses referred between 2017-2020 because of suspected structural abnormalities before/at/after STAS. Additional prenatal investigations and postnatal follow-up were searched. Abnormalities were classified into 'always', 'sometimes' and 'never' detectable in the first-trimester based on a previously suggested classification. RESULTS Of the 547 pregnancies, 13 (2.6%) received FTAS and 534 (97.6%) received a dating ultrasound and STAS. In 492/534 (92.1%) anomalies were confirmed; 66 (13.4%) belonged to the 'always detectable' group in the first trimester, 303 (61.6%) to the 'sometimes detectable' and 123 (25.0%) to the never detectable. Of the 'always detectable' anomalies 29/66 (44%) were diagnosed during dating ultrasounds and 37 (56%) during STAS. The rate of TOP for anomalies detected during FTAS and at/after STAS was 84.6% (n=11/13) and 29.3% (n=144/492) (p<0.01). CONCLUSION When FTAS is not part of screening paradigms, most fetal anomalies remain undetected until the second trimester or later in pregnancy, including 56% of anomalies 'always detectable' in the first trimester. This article is protected by copyright. All rights reserved.