If fetal and neonatal alloimmune thrombocytopenia (FNAIT) is suspected during pregnancy, a Monoclonal Antibody Immobilization of Platelet Antigens (MAIPA) test is a standard part of the diagnostic process.
In cases of FNAIT, this noninvasive test detects the presence of maternal antibodies to the fetus’s human platelet antigens (HPAs). Early detection of FNAIT is essential to guide prenatal management and ensure the best outcomes for the fetus.
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.
What is a MAIPA test?
An integral part of diagnostic testing, the MAIPA test is considered to be the most sensitive and specific test for detecting antibodies against specific fetal antigens. It requires a blood sample from the mother that is then sent to a specialized laboratory for analysis. If maternal antibodies against fetal antigens and fetal bleeding or hemorrhaging are detected, a diagnosis of FNAIT is made.
Diagnostic testing for FNAIT
During pregnancy, FNAIT may be suspected if bleeding or hemorrhage in the fetus is identified on an ultrasound. If there is no previous history of FNAIT but there is reason to believe the fetus may be at risk, diagnostic tests will be performed.
Until recently, fetal genotyping required a fetal blood sample obtained by cordocentesis, which put the fetus suspected of FNAIT at risk of bleeding and hemorrhage. When fetal platelet levels are low, the blood no longer clots and even minor procedures can cause life-threatening bleeding, intracranial hemorrhage and even miscarriage in severe cases.
Now, cell-free fetal DNA (cffDNA) screening can be used, which is a highly accurate, noninvasive test that tests genetic material from the pregnant mother’s blood plasma to determine the fetal HPA genotypes. Those genotypes are then compared with those of the mother to check for HPA incompatibility.
Regular ultrasounds can help monitor the fetus for bleeding and intracranial hemorrhage throughout the pregnancy.
Prenatal and postnatal FNAIT treatment
When FNAIT is confirmed during pregnancy, it guides treatment both prenatally and postnatally. During pregnancy, thrombocytopenia or low platelet count is treated with intravenous immunoglobulin (IVIG) therapy with or without steroids, which suppresses the pregnant mother’s immune system to reduce the production of maternal antibodies and slow the fetus’ progression towards severe thrombocytopenia.
An early delivery may be required if the fetus experiences complications, and a platelet transfusion after delivery can boost platelet levels and reverse the effects of thrombocytopenia.
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