Congenital Diaphragmatic Hernia (CDH) occurs in approximately 1 in every 2,500 births (1,600 cases in the U.S. each year). The cause of CDH is not yet known. The diaphragm is formed in the first trimester of pregnancy and controls the lungs' ability to inhale and exhale. CDH occurs when the diaphragm fails to form or to close totally and an opening allows abdominal organs into the chest cavity. This inhibits lung growth.