Each year in the United States, about 150,000 babies are born with birth defects ranging from mild to life threatening. The three leading categories of birth defects are structural/metabolic, congenital infections, and other conditions. While progress has been made in the detection and treatment of birth defects, they remain the leading cause of death in the first year of life. Birth defects are often the result of genetic and environmental factors, but the causes of well over half of all birth defects are currently unknown. The following is a brief sketch of the most commonly noted birth defects.