Jaundice of 18mg/dl in a newborn baby at 12 days suggests a high likelihood of pathologic jaundice. Common causes include: excessive bilirubin production, hepatic bilirubin metabolism disorders, bile excretion disorders and so on. 1. Excessive bilirubin production: due to increased destruction of red blood cells, resulting in increased bilirubin. Including ABO hemolytic disease, etc. 2. Hepatic bilirubin metabolism disorder: decreased liver function leads to elevated unconjugated bilirubin. Commonly, there are hypoxia, infection, etc. 3. Obstruction of bile excretion: bilirubin excretion is obstructed, leading to elevated bilirubin, commonly seen in congenital biliary atresia. Newborn baby 12 days jaundice 18mg/dl, there may be other reasons, it is recommended to go to the hospital in time, improve the examination to clarify the cause of the disease, under the guidance of the doctor to give targeted treatment or treatment.