Second trimester cardiac diagnosis: screening standards and outcomes

Second trimester screening for congenital heart defects occurs during the routine 18-20 weeks' anomaly scan in many countries. Most congenital heart defects can be prenatally detected by experts in foetal echocardiography working in tertiary centres with high-risk pregnancies. Many studies, however, have shown that detection rates obtained by experts are not reproducible in the low-risk peripheral practices where most of the foetal screening takes place. As the majority of foetuses with congenital heart defects are born to mothers with no identifiable risk factors, it is important that widespread screening of the low-risk population occurs. To facilitate this, standard protocols have been introduced in several countries, but they are not universal and have differing sensitivities depending on the screening views advocated and the area studied. Initially, only performing the four-chamber view (basic scan) was advocated. By adding the outflow tract views (extended scan), three-vessel, and laterality views, the sensitivity of the examination can be significantly increased. Unfortunately, the sensitivity of these extended protocols still does not meet that obtainable in experienced hands, reflecting the additional skill required to obtain these extended views. Thus, close links are required between the tertiary centres and the screening centres to teach and maintain the skills required to obtain and interpret the required views, and to support the sonographer's commitment. Furthermore, an audit system is required to trace false-positive and -negative cases so that targeted interventions can be planned. This is important, as a missed case of prenatal congenital heart defect is potentially a missed opportunity to reduce postnatal morbidity and mortality.