The severity of fetal and neonatal alloimmune thrombocytopenia (FNAIT) can vary significantly—some patients may be relatively symptom-free, while others may experience life-threatening consequences.
In all cases, being aware of possible FNAIT symptoms can facilitate early detection, and early treatment is crucial to achieving the best outcomes for the baby. If an FNAIT diagnosis is missed or delayed, the consequences for the baby can be life-threatening.
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.
As the mother’s antibodies attack the baby’s blood platelets, they progressively break down, leading to thrombocytopenia or a low platelet count. Blood loses its ability to clot and stem bleeding, causing uncontrollable bleeding and even hemorrhage.
Normal platelet levels range from 150,000 to 450,000 per microliter, and a low platelet count is below 150,000 per microliter.
Learn more about FNAIT testing and diagnosis
Mild FNAIT (platelet count below 150,000 per microliter)
In mild FNAIT, newborns can be symptom-free but have a low platelet count that is detected by a routine blood test. Close monitoring is still required to be sure that the baby doesn’t develop symptoms, and that the platelet count stays stable and doesn’t drop.
Moderate FNAIT (platelet count between 30,000 and 100,000 per microliter)
Often only diagnosed after birth, moderate FNAIT is detected by symptoms such as bruising, purple or red skin discoloration called purpura, pinprick bleeding under the skin called petechiae, bleeding, a low platelet count and blood collecting under the scalp and causing a bulge, also known as cephalohematoma.
Newborns can also be fatigued, irritable and show fussiness when feeding. Without immediate treatment via platelet transfusion, additional symptoms can develop or become more severe. Platelet transfusions can increase the platelet count, allowing the blood to clot and alleviate symptoms.
Severe FNAIT (platelet count under 30,000 per microliter)
The most severe complication of FNAIT is intracranial hemorrhage (ICH). This symptom is rare and occurs when the baby’s blood platelets become very low, causing blood vessels to rupture. Since the blood does not clot correctly in these infants, hemorrhaging may occur.
ICH or bleeding on the brain most often occurs in FNAIT-affected babies during pregnancy and is detected via ultrasound. Detection anytime after pregnancy, such as following delivery, can have a negative affect on outcomes. ICH can be life-threatening and cause long-term disabilities such as neurological damage, seizures, cerebral palsy, blindness and deafness.
Urgent platelet transfusions are required to boost the platelet count and stop the bleeding.
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