Why are congenital heart defects being missed?

OBJECTIVES: Congenital heart defects (CHD) are still frequently missed in prenatal screening programs, which can result in severe morbidity or even death. This case-control study evaluated the original images of the second-trimester standard anomaly scan (SAS) images to explore reasons for a missed prenatal diagnosis.

METHODS: All cases born with severe CHD in 2015-2016 were extracted from the PRECOR registry. Severe CHD was defined as requiring surgical repair in the first year of life. All cardiac views in the SAS (4CV, 3VV, LVOT, RVOT) were scored on technical correctness [range 0-5] by 2 fetal echo experts, blinded for the diagnosis and whether it was prenatally detected or not.

RESULTS: A total of 114 cases were analysed, comprising 17% transposition of the great arteries, 16% aortic coarctation, 10% Fallot's tetralogy, 6% atrioventricular septal defect, 5% aortic valve stenosis, 18% ventricular septal defect and 28% miscellaneous defects. No differences were found in fetal position, obstetric history, maternal age or gestational age at examination between missed and detected cases. The missed group scored significantly worse on the quality of the cardiac scan (adequate score in 36% vs 68%; p=0.002), proper use of magnification (58% vs 84%; p=0.01) and scores on each individual cardiac planes (4CV [2,7 vs 3,9; p<0.001], 3VV [3,0 vs 3,8; p=0.02], LVOT [1,9 vs 3,3; p<0.001] and RVOT [1,9 vs 3,3; p<0.001]). In 31% of the missed cases, images showed an abnormality, which had not been recognized at time of the scan (mainly septal defects and aortic arch anomalies), whereas in 20% of missed cases the cardiac planes were properly obtained, but showed normal anatomy.

CONCLUSIONS: Lack of adaptational skills appear to play an important role in undetected CHDs, as opposed to circumstantial differences, such as BMI or fetal position. The quality of the cardiac views was significantly more often inadequate in undetected versus detected cases. Despite adequate quality of the images, the CHD was not recognized in 31%. A high sonographer's SAS volume, performed in a large ultrasound center, significantly contributes to prenatal detection. In 20% of the undetected cases the CHD was not visible, even though the quality of the images was good. This article is protected by copyright. All rights reserved.