Structural abnormalities of the body that develop during embryogenesis and the fetal period; also called birth defects. Children with significant birth defects need more medical care than other children do, require more frequent hospitalizations, need community support services, and often require special education programs. Among children, over half of all visits to subspecialty medical clinics and admissions to hospitals are for treatment of disorders resulting from errors in embryonic development, chromosomal abnormalities, and genetic and familial disorders. Two-thirds of the deaths of infants and children in pediatric hospitals in developed countries are caused by underlying congenital anomalies.