What observation is most likely in a newborn with hemolytic disease?

In a newborn with hemolytic disease, the most likely observation is jaundice. This condition occurs when there is an excess breakdown of red blood cells, which leads to an increased level of bilirubin in the bloodstream. The liver of a newborn, which is still maturing, may be unable to process the excess bilirubin effectively, resulting in the yellowish discoloration of the skin and eyes known as jaundice.

Jaundice often becomes noticeable within the first few days of life and can be a key indicator of hemolytic disease, especially in cases related to Rh or ABO incompatibility. Immediate identification and management of jaundice are crucial, as untreated high levels of bilirubin can lead to serious complications, including kernicterus, which can have long-term effects on the newborn's neurological health.

Other options like polycythemia and splenomegaly may occur in certain contexts but are not the most characteristic observations associated specifically with hemolytic disease in newborns. Hot flushed skin does not typically relate to this condition either.