For hundreds of years, doctors, nurses and midwives have visually examined newborn babies for the yellowish skin tones that signify jaundice, judging that more extensive jaundice carried a greater risk of illness. Usually jaundice is transitory, but when it persists at severe levels, the baby may have a potentially serious condition called hyperbilirubinemia. Now researchers say that this longstanding practice of visual inspection is unreliable in predicting the baby’s risk of hyperbilirubinemia.