Co-occurrence of developmental disabilities with birth defects.

This article begins with a discussion of the concepts of comorbidity and co-occurrence of diseases and health conditions. These concepts are then applied to the literature on the population-based prevalence of developmental disabilities and birth defects. Most of the existing literature focuses on co-occurrence and obtains data from both clinical and administrative sources. Developmental disabilities occur more frequently in children with multiple, rather than with isolated, birth defects. More research, with more sophisticated study designs, will be necessary to further elucidate the contributions of birth defects to the etiology of developmental disabilities, control for other risk factors, and to identify strategies for prevention and intervention services.