Fetal and neonatal alloimmune thrombocytopenia (NAIT) is a blood disorder that affects pregnant women and their babies. NAIT was first reported in the literature in 1953 and is estimated to occur in as many as 1 in 1200 live births. NAIT results in the destruction of platelets in the fetus or infant due to a mismatch between the mother's platelets and those of the baby. Certain molecules (antigens) on the surface of the baby's platelets are recognized as foreign by the mother's immune system. The mother's immune system then creates antibodies that attack and destroy the baby's platelets. Though NAIT can occur whenever the mother's blood mixes with that of the baby, it is usually triggered when the mother is exposed to the baby's blood during delivery. Many cases of NAIT are mild. Signs and symptoms may include a low platelet count (thrombocytopenia) and signs of bleeding into the skin such as petechiae and purpura. In the most severe cases, NAIT can cause bleeding episodes that may result in death or long-term disability. Bleeding episodes can occur either during pregnancy or after birth.