There is no standard screening program for fetal and neonatal alloimmune thrombocytopenia (FNAIT), which means that it often goes undiagnosed during pregnancy.
Symptoms in the fetus often go unnoticed initially, and the most common symptoms in utero include bleeding and hemorrhage, as the infant’s blood may lose its ability to clot. It is typically diagnosed via a blood test after an infant is born, and physical symptoms may include bleeding and bruising on the skin.
Early diagnosis and treatment are essential for the best outcomes, but because it is a rare disease, it is not yet part of standard prenatal testing. If you think you may be at risk of FNAIT, notify your doctor, and they may be able to perform a diagnostic test.
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 is FNAIT diagnosed during pregnancy?
Prenatal testing for FNAIT is available but not offered unless there is a known or suspected history of FNAIT. Diagnosis usually only occurs after symptoms appear, and non-invasive diagnostic tools such as HPA typing of the mother and father, antibody screening of the mother and cell-free fetal DNA testing can confirm diagnosis.
In some cases, FNAIT is identified as a risk factor due to previous FNAIT-affected pregnancies, a family history or prior knowledge of human platelet antigen (HPA) incompatibility. This requires close monitoring of the fetus throughout the pregnancy to ensure early diagnosis and treatment.
The risks of undiagnosed FNAIT
If left undiagnosed, severe cases of FNAIT can lead to permanent neurological damage as a result of intracranial hemorrhage (ICH), and in some cases, even miscarriage and stillbirth. However, FNAIT can also present with milder symptoms that are not detected during pregnancy and only become visible once the infant is born.
FNAIT may be suspected following delivery if a patient has specific symptoms, like low platelet count, unexplained bleeding, bruising, pinprick bleeding under the skin (petechiae) or reddish purple skin discoloration (purpura) and intracranial hemorrhage. Immediate treatment is the priority, and diagnosis is made later by confirming the HPA incompatibility between mother and baby.
The importance of prenatal screening
FNAIT is not included in standard prenatal testing in the U.S., leading to cases where diagnosis is missed or only confirmed at a later stage. If FNAIT is identified as a risk factor in a pregnancy, this changes the approach to prenatal care, ensuring fetal monitoring for any potential FNAIT symptoms.
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