developmental anomaly, any congenital defect that results from interference with the normal growth and differentiation of the fetus. Such defects can arise at any stage of embryonic development, vary greatly in type and severity, and are caused by a wide variety of determining factors, including genetic mutations, chromosomal aberrations, teratogenic agents, and environmental factors. Developmental anomalies are classified either according to the organ system affected, such as congenital heart defects, or according to the way in which the defect occurred, such as developmental failure or arrest, failure to atrophy or subdivide, fusion, splitting, incorrect migration, and misplacement. Most developmental defects are apparent at birth, especially any structural malformation, but some, especially those involving the organ systems, do not become evident until days, weeks, or even years later.
