There is currently no standard prenatal screening for fetal and neonatal alloimmune thrombocytopenia (FNAIT), which means that in first pregnancies, it is often detected in the newborn rather than during pregnancy.
If FNAIT occurs in a first pregnancy, the risk is higher that the disease will occur and be more severe in future pregnancies. Subsequent pregnancies, therefore, often receive more specialized care and closer monitoring.
What is FNAIT?
Fetal and neonatal alloimmune thrombocytopenia (FNAIT) is a rare, potentially life-threatening autoimmune disease that affects an infant’s blood platelets. It occurs when a pregnant mother’s immune system creates antibodies that attack and break down her baby’s blood platelets. This immune response is due to the fetus inheriting a human platelet antigen (HPA) from its father that the mother doesn’t possess.
Blood platelets stop bleeding by clotting the blood. As the fetus’ platelets are destroyed, its platelet levels can drop to dangerously low levels (thrombocytopenia), leading to bleeding and in more severe cases, hemorrhages of the brain (intracranial hemorrhage or ICH) and internal organs (stomach, lungs, spinal cord, eyes). If left untreated, the fetus risks long-term brain damage, cerebral palsy, seizures, intellectual disabilities, blindness and death.
Diagnosing FNAIT
Diagnosis and treatment become urgent when newborns present with symptoms such as bruising, and the reddish-purple skin discolorations petechiae and purpura, indicating a low platelet count. Diagnostic tests to identify FNAIT are important to inform treatment choices but they will also be of benefit to the management of future pregnancies.
To diagnose FNAIT in a newborn, the mother’s blood is tested for HPA antibodies and the HPA types of mother, father and newborn are also tested.
FNAIT’s effect on subsequent pregnancies
When FNAIT occurs in a first pregnancy, there is a 90% chance of infants in any subsequent pregnancies developing FNAIT. It may also occur earlier in the pregnancy, as the mother is already sensitized and will still have antibodies against the HPA inherited from the father.
Classified as high-risk for the fetus, a pregnancy at risk of FNAIT requires specialized care from a multidisciplinary team led by a maternal-fetal specialist and a hematologist. Close monitoring of the fetus by ultrasound and blood tests is required to check for abnormalities in the blood and internal organs.
To help delay the onset of FNAIT and avoid associated complications, the pregnant mother will likely receive weekly doses of intravenous immunoglobulin (IVIG), a blood product that contains antibodies from human donors. Corticosteroid therapy may also be administered.
If FNAIT does develop, early proactive intervention during pregnancy has been shown to improve outcomes and prevent ICH, the most dangerous complication of FNAIT.
