RDMS (Registered Diagnostic Medical Sonographer) is a credential awarded by the American Registry for Diagnostic Medical Sonography (ARDMS) to sonographers who meet education and experience requirements and pass the Sonography Principles & Instrumentation (SPI) examination plus at least one specialty exam. RDMS specialty options include Abdomen (AB), Obstetrics & Gynecology (OB/GYN), Breast (BR), Fetal Echocardiography (FE), and others. The RDMS is one of the most widely recognized sonography credentials in the United States.