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. Management of the infant with neonatal alloimmune thrombocytopenia may include platelet transfusions, ultrasounds, and intravenous immunoglobulin (IVIG). Treatment for pregnant mothers at risk for NAIT may include IVIG and steroids. 

Some cases of NAIT are mild. The most common sign is bleeding into the skin which may present as petechiae or localized swellings (hematomas). In more severe cases, the infant may experience bleeding episodes affecting the brain or major organs. These bleeding episodes can be life-threatening. 

As there is no universal screening test for NAIT, the first case of NAIT in a family is often unexpected. However, there is a high recurrence risk for NAIT and consultation with a maternal-fetal medicine specialist or other professional with experience treating NAIT is indicated in future pregnancies once a diagnosis of NAIT is made. Blood tests performed on the mother, father, and baby can be used to decide which pregnancies/babies are at risk.

Management for pregnancies determined to be at risk remains controversial but may include a planned delivery and maternal avoidance of nonsteroidal anti-inflammatory drugs (NSAIDS) and aspirin during pregnancy. Management strategies have also included maternal intravenous immunoglobulin (IVIG) or maternal steroids and more invasive procedures such as fetal blood sampling and fetal platelet transfusions. The less invasive approach is currently favored.

Management of the affected infant after birth depends on the specific signs and symptoms but may include periodic ultrasounds of the brain to check for bleeding, platelet transfusion, and IVIG. In the absence of intracranial bleeding, the prognosis is generally favorable and the platelet count usually improves within 8 to 10 days.