Abstract
One hundred and thirty five consecutive fetuses of between 16 and 23 weeks' gestation that were considered to be at high risk of having structural heart defects were examined prospectively to determine the reliability of echocardiography for diagnosing such defects in mid trimester. Each echocardiogram was done in a standard manner and cardiac anatomy was analysed segmentally. Twelve fetuses were excluded from analysis because of lack of follow up. Of the remaining 123 fetuses, 109 had no evidence of heart disease when followed up. In this group the prenatal echocardiogram was normal in 105 and technically inadequate in four; thus there were no false positive diagnoses of heart disease in fetuses subsequently shown to have normal hearts. Fourteen had heart defects at follow up. The serious defect was correctly diagnosed prenatally in 10 of 14 cases, whereas in the other four the prenatal echocardiogram was considered normal. Some errors were made in diagnosing associated segmental defects particularly if the heart disease was complicated. Therapeutic abortion was carried out in seven cases; in five of the fetuses the prenatally diagnosed heart defect was the sole or an important contributing reason for the abortion. We conclude that echocardiography is a reliable method for diagnosing many heart defects in the mid trimester.