Sir.—Cooper et al1 presented the results of their excellent study correlating echocardiographic findings of fetuses and infants of diabetic mothers with indexes of maternal diabetic control. Unfortunately, they failed to provide enough information on the echocardiographic data to allow assessment of the accuracy of their calculation of 31% prevalence of asymmetric septal hypertrophy (ASH). In addition, we believe that they used the term ASH inappropriately.
The authors acknowledge that the septum is normally thicker in the fetus, and that this disproportion rarely causes left-ventricular outflow obstruction; nevertheless, they use a ratio of the septal to left ventricular free-wall thickness of 1.3:1 as one of their two criteria for determining whether an infant has ASH. Maron et al,2 in a definitive study of the normal developing heart, recommended the use of the term disproportionately thickened septum rather than ASH because the fetus normally has a septum that is