DIXON, Tenn. — When Shelby Martin began experiencing intense pain during her third pregnancy, she sensed something was different. The 30-year-old mother of four said the discomfort was beyond anything she had felt before, later discovering that the sensation came from carrying a record-breaking baby. Martin gave birth to her son, Cassian, on July 29 at Tristar Centennial Women’s Hospital in Nashville. Weighing in at 12 pounds, 14 ounces, Cassian was one of the l