The ParaGuard IUD, which releases copper into the uterine cavity, can last up to 10 years. In clinical studies, the pregnancy rate among women using the device was less than 1 pregnancy per 100 women annually. Mark Harmel/Science Source hide caption

itoggle caption Mark Harmel/Science Source

Medical residents including Dr. Amy Ho (bottom right) helped with first aid at the Pitchfork Music Festival in Chicago. Courtesy Amy Ho hide caption

itoggle caption Courtesy Amy Ho

Michael Sawyer, the latest doctor in his family, holds a portrait of his grandfather Dr. Ken Sawyer, while his father Robert, a surgeon, looks on. Barry Gutierrez for NPR hide caption

itoggle caption Barry Gutierrez for NPR

To reduce errors by doctors in training, medical educators have capped how long they can work. But enforcing the limits can be a challenge. iStockphoto hide caption

itoggle caption iStockphoto