Low platelet levels are a key symptom in babies affected by fetal and neonatal alloimmune thrombocytopenia (FNAIT) and indicate a risk of bleeding and hemorrhage. However, babies who have experienced FNAIT during pregnancy may have normal platelet levels at birth, and yet still present with bleeding.
Platelet levels can fall quickly following birth, and maternal antibodies continue to break down the baby’s blood platelets. Close monitoring of blood platelet levels and other symptoms, plus urgent treatment of any bleeding, are key to good outcomes.
What is FNAIT?
Fetal and neonatal alloimmune thrombocytopenia (FNAIT) is a rare but serious condition that affects 0.1% of pregnancies in which a pregnant mother’s immune system produces antibodies against the platelets of her fetus. This occurs when a fetus inherits platelet antigens from the father that are not compatible with the mother, typically involving a protein called human platelet antigen (HPA). The mother’s immune system recognizes the fetal platelets as foreign, attacking and destroying them, leading to low platelet levels (thrombocytopenia) in the fetus or newborn.
How can an infant with FNAIT have normal platelet levels?
When a pregnancy is affected by FNAIT, the fetus risks bleeding from small events like burst blood vessels or minor invasive medical procedures. When platelet counts are low, the blood doesn’t clot, leading to uncontrolled bleeding and hemorrhage. Intracranial hemorrhage (ICH) is the most severe, with potentially life-threatening consequences.
The recommended prenatal treatment of FNAIT is via intravenous immunoglobulin (IVIG) with or without steroids to reduce the onset of severe thrombocytopenia. This has been shown to improve fetal platelet levels by suppressing the production of maternal antibodies and reducing the number of existing maternal antibodies that cross the placenta.
Learn more about FNAIT signs and symptoms
As IVIG is administered until delivery, the baby can be delivered with normal platelet levels. However, platelet levels can quickly drop following delivery and then continue to fall, leading to bleeding.
What to do if you suspect FNAIT with initially normal platelet counts
If FNAIT has been treated during pregnancy, a platelet transfusion won’t be given unless platelet levels are low. However, if bleeding in the brain is detected, which may have originated during pregnancy, a platelet transfusion may be advised. In addition, if high levels of maternal antibodies are detected in the newborn’s blood, there is a clear risk that platelet levels will fall.
In the days following birth, it is essential to monitor the newborn for the appearance of other FNAIT-related symptoms such as bruising, petechiae and purpura, check platelet levels regularly and screen for internal bleeding such as in the brain or the gastrointestinal system.
Maternal anti-HPA antibodies can remain in the newborn’s blood for two to six weeks after birth, so it is important to monitor the level of maternal antibodies in the newborn’s blood. Delayed bleeding in the FNAIT-affected newborn can still develop in the weeks following birth if platelet levels drop.
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