ObjectiveTo determine whether there is a difference between the types of cardiac lesions detected as abnormal prenatally and those that are not detected.MethodsConsecutive fetuses at 14 weeks' gestation or more were scanned in our unit from February 1990 through July 1995 and later were delivered at our hospital. Outcome information was obtained from neonatal echocardiograms and autopsies. Our results were compared to sensitivities for individual cardiac lesions based on pooled data from studies published previously.ResultsThere were 111 fetures with cardiac anomalies, of which 73(66%) were identified correctly as abnormal prenatally. Senitivities for the most common cardiac lesions were as follows: 87% atrioventricular septal (endocardial cushion) defects, 65% tetralogy of Fallot, 63% transposition of the great arteries, 50% aortic coaractation, and 445 isolated ventricular septal defects. The lesions that went undetected most frequently were isolated septal defects (n= 17); most of these were ventricular and small or moderate in size. Based on our sensitivities and those calculated from previous studies, the fetal cardiac lesions with the highest detection rates involve hypoplastic ventricles and atrioventricular septal defects, followed by lesions of the great arteries and finally by isolated septal defects.ConclusionsThe sensitivity of sonographic screening to detect fetal cardiac anomalies varies with the type of lesion. Isolated septal defects are the most difficult lesions to detect.