BACKGROUND:

Congenital heart disease represents a major segment of clinically significant birth defects and is associated with high mortality and morbidity in infancy, a childhood marred with physical limitations and repeated invasive procedures, and an adulthood with increased risk of medical and social problems. Previous research has been principally directed to clinical methods of diagnosis and treatment, but the need for prediction and prenatal counseling requires further knowledge of environmental and familial risk factors. Congenital heart disease is not one of the malformations monitored by the International Clearing House of Birth Defects Surveillance System. Surveillance which does include congenital heart disease may lack diagnostic accuracy among the various reporting sources. Accurate clinical studies lack comparative control information. As a result, the true epidemiologic features of cardiac defects remain obscure.

DESIGN NARRATIVE:

The design of the Baltimore-Washington Infant Study was that of a case-control study. All infants under one year of age with confirmed diagnoses of congenital heart disease were eligible for inclusion if they were residents of the study area which encompassed 53 area hospitals in Maryland, the District of Columbia and five counties in Virginia. Case enrollment was done through five pediatric cardiology centers and through a periodic search of the obstetrics and neonatal and pathology logs of the participating hospitals. Control selection was by random numbers and all resident births were eligible as controls except for those with congenital heart disease. Mothers of cases and controls were interviewed at home for demographic information, and information on maternal health, maternal medication, reproductive history, lifestyle, environmental exposures in the home, occupation, and agents transmitted to the mother by the father. Data were collected on the characteristics, drug use, habits, and occupations of the fathers. Vital records and birth certificates were abstracted for all cases and controls. Death certificates were also abstracted. Variables including drugs, lifestyle and home exposures, and occupation, were screened to identify which single factors were most importantly related to congenital heart disease.

Cases in which congenital heart disease was part of a genetic complex were evaluated separately for environmental exposures. Genetic data analysis focused on first degree relatives but extended family data were noted wherever available. The genetic data analyses included: estimation of recurrence risks in siblings for congenital heart disease with the same cardiac defect; any cardiac defect in the sibling; non cardiac birth defect and pregnancy loss in the family. Parental phenotype was investigated for the presence of birth defects and known genetic disorders. Twin births were assessed for concordance in zygosity. Hypotheses of genetic and environmental teratogenic and coteratogenic interactions were tested. Pathogenic mechanisms were further defined through anatomic and echocardiographic observations. The family inquiry was expanded to include cousins. Nutrition information was added on maternal vitamin A supplementation, protein, calories, and other nutrients.