In pregnancies affected by fetal and neonatal alloimmune thrombocytopenia (FNAIT), the mother’s immune system develops antibodies against the fetal human platelet antigens (HPAs) that have been inherited from the father.
While these antibodies stay in the mother’s system for life, their presence in newborns with FNAIT is temporary. They are gradually eliminated from the baby’s bloodstream in the weeks and months following delivery, with no long-term impact if FNAIT has been effectively treated.
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 are anti-HPA antibodies?
A fetus inherits two antigen alleles—one from its mother and the other from its father. If the fetus inherits an antigen that the mother doesn’t have, the mother identifies it as foreign and produces antibodies to destroy it. This incompatibility is rare, and it doesn’t always lead to FNAIT.
How long do anti-HPA antibodies stay in the mother’s system?
When a new pregnancy is planned or confirmed, the mother’s anti-HPA antibody levels will be tested, and the results can reliably predict if someone is at risk of FNAIT.
Learn more about FNAIT testing and diagnosis
Maternal anti-HPA antibodies don’t leave the mother’s system once they have been produced, although they can decline over time. The risk of FNAIT has implications for future pregnancies in terms of how prenatal care is managed. In subsequent pregnancies, as the maternal antibodies are pre-existing, FNAIT often occurs earlier and with more severe symptoms. FNAIT reoccurs in future pregnancies at a rate of 90%.
Close monitoring, regular blood tests to monitor maternal antibody levels and ultrasounds to check for bleeding in the baby are essential to ensuring early detection. Preventative treatment with intravenous immunoglobulin (IVIG), with or without corticosteroids, can help prevent the onset of severe thrombocytopenia, with life-threatening complications for the fetus such as intracranial hemorrhage (ICH).
How long do anti-HPA antibodies stay in the baby’s system?
The mother’s anti-HPA antibodies can stay in the newborn’s blood for several weeks, and in some cases, months. Regular blood tests can monitor the levels to track the elimination of the antibodies, because as long as the antibodies remain in the baby’s system, bleeding and complications may still occur.
Platelet transfusions are often recommended to treat thrombocytopenia in newborns, which allows the blood to clot. The baby’s platelet count is closely monitored to be sure it is gradually increasing.
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