Rh incompatibility occurs when an Rh-negative pregnant woman carries an Rh-positive baby. The baby can inherit the Rh protein from the father, making them Rh-positive. During pregnancy, red blood cells from the fetus can cross the placenta into the mother's bloodstream. If the mother is Rh-negative, her immune system recognizes these Rh-positive fetal cells as foreign and begins to produce antibodies against them. These antibodies can then cross the placenta into the developing baby's circulation and attack the baby's red blood cells, causing them to break down. This destruction of red blood cells leads to the production of bilirubin and can result in jaundice (yellowing of the skin and eyes) in the baby. Bilirubin levels in the baby's blood can range from mild to dangerously high, with the risk typically peaking near or at delivery. Usually, a mother's first Rh-positive baby is not affected because it takes time for the mother to develop sufficient antibodies. However, subsequent Rh-positive pregnancies may be negatively impacted by the mother's pre-existing antibodies.