Blood group incompatibility occurs when a person receives blood from a donor with a different blood type, leading to an immune response. This can happen during blood transfusions or pregnancy if the mother and baby have incompatible blood groups, such as ABO or Rh incompatibility. The immune system may attack the foreign blood cells, causing serious health issues. In pregnancy, if a mother with Rh-negative blood carries a baby with Rh-positive blood, her body may produce antibodies against the baby's blood cells. This can lead to conditions like hemolytic disease of the newborn, which can cause anemia or jaundice in the baby. Proper medical care can help manage these risks.