Undetected cases after implementation of first-trimester anomaly scan in low-risk population: insights from the IMITAS study

Sep 28, 2026

Uploaded by Jake

The study evaluates the effectiveness of the first-trimester anomaly scan (FTAS) within a centrally steered Dutch national screening program by analyzing false-negative fetal structural anomalies not detected at FTAS. It is a secondary analysis of the IMITAS prospective cohort (Nov 2021–Nov 2022, low-risk population). Cases were diagnosed before 24 weeks after tertiary referral based on second-trimester findings, then classified by first-trimester detectability and examined via blinded fetal image quality scoring.

LanguageEnglish

CategoryHealthcare

FormatPDF

Pages7

Reading Time18 min

AccessFree to download

ABSTRACT

Objective

Methods

Results

Conclusions

INTRODUCTION

Ultrasound Obstet Gynecol 2026; 67: 27–33 Published online 14 November 2025 in Wiley Online Library ([wileyonlinelibrary.com](wileyonlinelibrary.com)). DOI: 10.1002/uog.70131. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited. Undetected cases after implementation of ﬁrst-trimester anomaly scan in low-risk population: insights from the IMITAS study K. BRONSGEEST1 , E. E. R. LUST2 , S. C. E. ZAAIJER1 , L. HENNEMAN3,4 , N. CROMBAG2 , C. M. BILARDO5, R.-J. H. GALJAARD6 , E. SIKKEL7 , A. K. K. TEUNISSEN1 , M. N. BEKKER2 , M. C. HAAK1 and Collaborators† 1 Department of Obstetrics and Gynecology, Leiden University Medical Center, Leiden, The Netherlands; 2 Department of Obstetrics and Gynecology, University Medical Center Utrecht, Utrecht, The Netherlands; 3 Department of Human Genetics, Amsterdam UMC, location Vrije Universiteit Amsterdam, Amsterdam, The Netherlands; 4 Amsterdam Reproduction and Development Research Institute, Amsterdam UMC, location Vrije Universiteit Amsterdam, Amsterdam, The Netherlands; 5 Department of Obstetrics and Gynecology, Amsterdam UMC, Amsterdam, The Netherlands; 6 Department of Clinical Genetics, Erasmus University Medical Center, Rotterdam, The Netherlands; 7 Department of Obstetrics and Gynecology, Radboud University Medical Center, Nijmegen, The Netherlands KEYWORDS: early diagnosis; fetal anomaly; fetal screening; prenatal detection; prenatal ultrasonography | ABSTRACT
Objective To assess the effectiveness of the ﬁrst-trimester anomaly scan (FTAS) performed as part of a centrally steered national screening program in The Netherlands by investigating false-negative cases with a fetal structural anomaly that was not detected at the FTAS.
Methods This was a secondary analysis ofthe IMplementation of fIrst Trimester Anomaly Scan (IMITAS) study, a national prospective cohort study conducted in a low-risk population in The Netherlands between November 2021 and November 2022 . TheFTAS was performed according to a predeﬁned scanning protocol. We collected all cases with a fetal structural anomaly that was not detected at the FTAS and was diagnosed at a tertiary care center before 24 weeks’ gestation following a referral based on the second-trimester anomaly scan. These anomalies were classiﬁed as: (1) ‘always detectable’ in the ﬁrst trimester (e.g. holoprosencephaly, anencephaly), referred to as ﬁrst-trimester major anomalies (FTMAs); (2) ‘often detectable’ in the ﬁrst trimester (e.g. spina biﬁda, major heart defect); or (3) ‘undetectable’ in the ﬁrst trimester (e.g. agenesis of the corpus callosum) . To investigate the reasons for undetected FTMA, sonographic images from these cases and from a sample of normal controls were retrieved and scored for quality by two fetal medicine experts, who were blinded to the fetal outcome. | Results Of the 127 979 cases with a normal FTAS result, 1164 (0. 9%) had a fetal structural anomaly diagnosed before 24 weeks’ gestation. Seven cases could not be categorized because intrauterine fetal death occurred before arrival at the tertiary care center. Among the 1157 remaining cases with an undetected anomaly, 23 (2 .0%) had a FTMA, comprising mainly limb reduction defects, hydrops and megacystis, with seven cases of multiple congenital anomalies. A further 126 (10.9%) cases had an anomaly that is considered often detectable in the ﬁrst trimester, which primarily comprised cardiac defects and central nervous system anomalies. Lastly, 1008 (87.1%) cases had an anomaly that is considered undetectable in the ﬁrst trimester, represented mainly by urogenital and cardiac anomalies. Quality assessment of images obtained at the FTAS in 23 cases with undetected FTMA and 19 controls showed that the quality score for fetal anatomy was signiﬁcantly lower in cases vs controls (P = 0.003), with mandatory planes missing

FAQs

What was the main objective of the IMITAS analysis?

To assess the effectiveness of the first-trimester anomaly scan by investigating fetal structural anomalies that were not detected at FTAS but were diagnosed before 24 weeks.

How were undetected anomalies classified in the study?

They were categorized as first-trimester major anomalies (always detectable), often detectable anomalies, or undetectable anomalies in the first trimester.

What were the key reasons for missed major anomalies?

The main reasons were missing mandatory planes and obtaining suboptimal ultrasound planes during FTAS.

Sep 28, 2026

Uploaded by Jake