Pregnancies affected by fetal and neonatal alloimmune thrombocytopenia (FNAIT) are considered high-risk and require a high level of prenatal care. Even if the fetus has stable platelet counts, an early delivery may still be advised.
This is due to the risk created if the mother has high HPA antibodies. The longer the fetus stays in the womb, the more toxic the environment becomes, with maternal antibodies constantly attacking the fetus’s blood platelets. An early delivery avoids unnecessary risks of birth trauma and allows for platelet transfusions to the newborn to treat thrombocytopenia.
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.
Detecting FNAIT during pregnancy versus post-delivery
Diagnostic tests can be performed on the newborn to confirm an FNAIT diagnosis both during pregnancy and after delivery. Once FNAIT is identified during pregnancy, regular administration of IVIG, with or without corticosteroids, helps boost the fetus’s immune system and protect its blood platelet levels by suppressing the mother’s immune response.
FNAIT is more commonly detected and diagnosed post-delivery, when newborns present with symptoms such as a pinprick red rash called petechiae or purple skin discoloration called purpura, bruising, unexplained bleeding or low blood platelets levels in initial blood tests. In pregnancy FNAIT is more difficult to diagnose.
Unless a risk has been identified as the result of family history or an earlier FNAIT-affected pregnancy, FNAIT is often only discovered as a result of bleeding or hemorrhage detected on an ultrasound.
Reasons for early delivery in FNAIT
There are a few main reasons why fetuses affected by FNAIT may be delivered early.
1. The longer the fetal blood platelets are attacked and destroyed by maternal antibodies, the greater the risk for uncontrollable bleeding or hemorrhage. Thrombocytopenia stops the blood from clotting, meaning the slightest injury can develop into a life-threatening bleed.
2. The onset of contractions and a vaginal delivery can cause trauma to the baby, leading to bruising, bleeding or life-threatening hemorrhages such as intracranial hemorrhage.
3. While blood platelets levels can be stable, they can easily fluctuate leading to complications.
4. The placenta can become damaged in late FNAIT pregnancy, restricting blood flow and potentially leading to complications.
Early delivery can be recommended from as early as 34 weeks if the risk of continuing the FNAIT pregnancy is assessed as high. More commonly, early delivery takes place from 37 weeks to allow the baby to receive treatment in the form of platelet transfusions.
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