Neutropenia is an abnormally low number of white blood cells. These cells, which are called neutrophils, help the body fight infection. White blood cells are produced in the bone marrow. They are released into the bloodstream, and travel wherever they are needed. Low levels of neutrophils occur when the bone marrow cannot replace them as fast as needed. A very severe infection may cause neutrophils to be used up quickly, and may also prevent the bone marrow from producing more neutrophils. In rare cases, mothers may have antibodies against their baby’s neutrophils. These antibodies cross the placenta before birth and cause the baby’s cells to break down (autoimmune neutropenia). In other rare cases, a problem with the baby’s bone marrow may lead to decreased white blood cell production. In many cases, neutropenia goes away on its own as the bone marrow recovers and begins to produce enough white blood cells.