Diagnosis of fetal cardiac abnormalities.

The feasibility of cross sectional imaging of the structure of the fetal heart was first described in 1980.1-3 Since then fetal echocardiography has been carried out in many pregnancies that are at increased risk of congenital heart disease, and more recently the study of one section of the fetal heart has been included in routine obstetric ultrasound examinations.4 These studies have yielded surprising results about the incidence, range, and natural history of congenital heart disease that may be seen prenatally. Also the pattern of recurrence of congenital heart disease within family groups does not seem to conform to previously accepted genetic theories. The mothers who are at increased risk of fetal heart disease include: those with a family history of congenital heart disease; those with diabetes; or those in whom fetal hydrops, arrhythmia, or an extracardiac anomaly has been found. Our most important source of detection of cardiac anomalies in recent years comes from apparently normal pregnancies in which the obstetrician has noticed an abnormal appearance of the heart on a routine scan. The idea of prenatal cardiac screening came from a French study first reported in 1985 (Fermont L, De Geeter B, Aubry MC, Kachaner J, Sidi D. A close collaboration between obstetricians and cardiologists allows antenatal detection of severe cardiac malformations by 2D echo. Abstract, Second World Congress of Pediatric Cardiology, New York, 1985). A small group of obstetricians was taught to visualise and understand the normal appearance of the four chamber view of the heart and incorporate this into their routine scan (fig 1). When difficulty was experienced in seeing the normal four chamber view the case was referred to a paediatric cardiologist for further evaluation. During a two year period, 20 000 pregnancies were screened, and 39 serious anomalies were detected. This is in accord with the expected figure of 2/1000 that might be detected by this view alone from analysis of data from infants.5 Screening for congenital heart disease is therefore possible, and it is now being increasingly practised in the United Kingdom. Our success has been less dramatic than the French, because most routine scans in this country are done at 16 weeks' gestation, whereas in France they are done at 20-24 weeks when the fetal heart can be seen more easily. Also some obstetric units in the United Kingdom are handicapped by poor ultrasound equipment or limited time available for adding extra work to the schedule. These problems are slowly being resolved, and we currently have a research programme that is trying to improve the quality and reliability of screening. Although there are still a substantial number of serious anomalies missed by this programme the referral pattern over the years has changed enormously as a result of teaching. Fig 2 shows the increasing number of anomalies detected since 1980, and the proportion of these diagnosed from routine scans. Although the overall frequency of 2 anomalies/ 1000 detected by the screening programme is consistent with the expected rate from postnatal