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In a series of 1600 pregnancies 34 cases of congenital heart disease were correctly identified by fetal echocardiography. In each case echocardiographic diagnosis was confirmed by anatomical study. Termination of pregnancy was done electively in 14 cases: in six because of the identification of a cardiac anomaly and in the remaining eight because of multiple congenital anomalies. The remaining 20 fetuses died subsequently owing either to the complexity of congenital heart disease or to associated extracardiac abnormalities, which were present in more than half the fetuses with congenital heart disease. There were eight errors in interpretation of the fetal echocardiogram. The outcome of the pregnancy was not influenced by the error in any case. Fetal echocardiography can predict correctly structural malformations of the heart. The technique is sufficiently reliable to give an accurate prognosis in early pregnancy and provide the basis for alterations in obstetric management.

The spectrum of congenital heart disease seen in a series of 72 fetal anomalies detected echocardiographically differed from that seen in infancy. This reflects the selection of patients for referral for fetal echocardiography and the high rate of natural fetal loss that occurs when severe cardiac defects are present.

Of 20 pregnancies referred for fetal echocardiography with a diagnosis of anterior abdominal wall defect, congenital heart disease was present in eight of the 17 with exomphalos and in none of the three with gastroschisis. Four of these eight affected pregnancies were terminated because trisomy 18 was diagnosed, of the remaining four, only one baby survived infancy. We conclude that ultrasound investigation of the fetal heart is an important part of the diagnostic assessment of anterior abdominal wall defect if an accurate prognosis and appropriate obstetric management are to be provided.

Nineteen pregnancies complicated by fetal congenital diaphragmatic hernia (CDH) referred for fetal echocardiography have been reviewed. Congenital heart disease was diagnosed prenatally in three fetuses; in one of these the pregnancy was terminated, the two other infants died in the neonatal period. The presence of the fetal stomach within the thorax or a hernia/heart area ratio greater than 1.7 was associated with a large diaphragmatic defect. Polyhydramnios was not associated with a poor postnatal outcome. Evidence of cardiac ventricular disproportion before 24 weeks gestation in isolated CDH was associated with 100% mortality. Development of ventricular disproportion during the third trimester was associated with a survival rate of 75%. In three fetuses, all of whom survived, no ventricular disproportion was detected during the third trimester examination.

Seven cases of pulmonary atresia with intact ventricular septum were detected in prenatal life. In two of these cases, there was a small hypertrophied right ventricle of the type commonly seen postnatally. In the remaining five cases, the right atrium and right ventricle were grossly dilated to a degree that caused lung compression. The resulting impairment of lung development appeared to be an important factor contributing to death in all five cases. Decompression of the right ventricle by intrauterine surgery to allow normal lung development in the last weeks of pregnancy may be the only way of changing this outcome.

The accuracy of the echocardiographic diagnosis of fetal heart disease in an experienced centre was evaluated by analysing the results achieved during 1987 at the Perinatal Cardiology Unit, Guy's Hospital. In this one year, 978 high-risk patients were referred for fetal echocardiography. Of these, 74 cases were found to have cardiac malformation, 69 of which were predicted from the prenatal study. Of the 69, the autopsy specimen was available for correlative purposes in 41 cases. A postnatal echocardiogram was performed by us in a further 15 cases. The result of autopsy or of a postnatal echocardiogram was obtained from another hospital in 7 cases. Postmortem was refused in 5 cases, while one further case remains alive but has not had a postnatal echocardiogram. Close correlation was achieved between the predicted echocardiographic diagnosis and the anatomical results. Some minor errors in the complete interpretation of a defect were found, particularly in those fetuses in whom image quality was poor, due to early (less than 20 weeks) or late (greater than 34 weeks) gestation or to maternal obesity. Difficulty in echocardiographic interpretation was also experienced in unusual defects. There was one false positive prediction of coarctation of the aorta. One major (total anomalous pulmonary venous drainage) and 5 minor abnormalities (two atrial and three ventricular septal defects) detected after birth were overlooked on the fetal study. Although the echocardiogram in prenatal life is not as accurate as it can be postnatally, with suitable experience a high degree of precision can now be achieved.

Pulsed wave Doppler estimates of blood flow velocity were made across the mitral, tricuspid, aortic, and pulmonary valves in a series of 120 normal fetuses (gestational age 16-36 weeks). In 36 of these the data were obtained in all four sites. The maximum and mean velocities were calculated for each valve and these values were plotted against gestational age. There was little change in these values throughout pregnancy. The orifice dimensions of the valves were measured by cross sectional echocardiography. At all ages the tricuspid orifice was larger than the mitral and the pulmonary orifice was larger than the aortic. The blood flow values for each valve were derived from the product of the mean velocity and the valve orifice dimensions. The output of the right ventricle was usually, but not always, greater than that of the left ventricle. Combined ventricular output increased from approximately 50 ml/min at 18 weeks to 1200 ml/min at term. Despite limitations in the accuracy of the technique these results form a useful basis for the analysis of blood flow in the normal fetus and for the interpretation of abnormal Doppler findings in prenatal life.

Fetal echocardiography can ascertain, at an early stage in pregnancy, recurrences of congenital heart disease (CHD) in mothers with a family history of CHD. In 1,021 mothers referred for this reason, 20 recurrences were found; 17 occurred when there had been 1 previously affected child, and 3 when there had been 2 previously affected children. No recurrences were found in the 41 cases in which a parent had CHD. The overall recurrence rate was 1 in 52 with a previously affected child and 1 in 10 with 2 previously affected children. However, certain forms of CHD recurred much more frequently than others. Aortic valve atresia was associated with a recurrence rate of 1 in 28, coarctation of the aorta at a rate of 1 in 15, complex CHD at a rate of 1 in 11 and truncus arteriosus at 1 in 13. These findings are inconsistent with previous family studies; this may be due to more complete ascertainment, particularly of major lesions, possibly overlooked by postnatal family studies because of fetal loss. Alternatively, the availability of prenatal diagnosis may be producing an increase in family size after major CHD. The results support current doubts on the polygenic theory of inheritance for all forms of CHD.

Thirty normal hearts from fetuses aborted at 10-33 weeks' gestation were measured directly and the results were compared with echocardiographic measurements in 20 normal live fetuses of 23-27 weeks' gestation. The diameters of the aorta, aortic isthmus, pulmonary arteries, and arterial duct were measured at standard levels and expressed as a ratio of the diameter of the ascending aorta. The ratios for the isthmus, the duct, and the right pulmonary artery were: 0.63 (0.11), 0.51 (0.13), 0.56 (0.10) respectively for the direct measurement and 0.73 (0.07), 0.7 (0.08), 0.62 (0.06) respectively at echocardiography. These results show that in mid-gestation the isthmus of the human fetus is not as small as that reported in animal models. This indicates that the distribution of the fetal circulation may not be the same either.