Pregestational Diabetes Mellitus and Congenital Heart Defects.

2219 Congenital heart defects (CHDs) comprise a wide range of malformations of the heart (ie, atrial and ventricular chambers and septa, and atrioventricular and semilunar valves) and great vessels (ie, the great arteries and systemic and pulmonary veins), reflecting the complexity of developmental processes and potential disturbances in morphogenesis of the cardiovascular system. The first published report on the spectrum of CHD phenotypes was an atlas of a systematic classification of CHDs based on pathophysiologic considerations of 1000 cases by Maude Abbott in 1936. Since then, the nomenclature and classification of CHD phenotypes have evolved with the development of surgical repairs and conduct of population-based studies into possible causes by using methods that account for potential etiologic heterogeneity among specific CHD phenotypes and groupings of phenotypes of similar developmental origin. More recently, the National Birth Defects Prevention Study further developed the classification of CHDs to account for variation of phenotypes based on the complexity of cardiac lesions present (ie, simple, associations, complex), and for the presence of disorders in other organ systems (ie, isolated or multiple/complex pattern), as well. These developments in nomenclature and classification, in turn, have facilitated more reliable assessments of trends in population-based prevalence of specific phenotypes of CHDs and standardized research methods for the purpose of identifying modifiable risk factors and potential prevention interventions for CHDs.