Learn The BasicsFetal and neonatal alloimmune thrombocytopenia (FNAIT) is a blood disease affecting babies before they are born or right after birth. It is a rare disease affecting around one in 1,500 pregnancies, but it is the most common cause of low platelet counts and/or thrombocytopenia in newborn babies.
The first case of FNAIT was reported in 1953.
What causes FNAIT?
FNAIT is caused by a pregnant woman’s immune system mistakenly attacking the platelets–fragments of blood that form clots and stop or prevent bleeding–of the baby.
This occurs when the baby’s platelets express a protein on their surface called human platelet antigen (HPA) that they inherited from their father and that is incompatible with the HPA of the mother.
The mother’s body recognizes these proteins as foreign and begins making antibodies that recognize them and mark them for destruction.
What are the symptoms of FNAIT?
The destruction of the baby’s platelets leads to thrombocytopenia.
This can lead to symptoms such as skin discolorations called petechiae and purpura, which is the result of bleeding under the skin, and the formation of severe bruises called hematomas. These can occur before or within a few hours after birth.
In more severe cases, bleeding can occur in major organs such as the gastrointestinal tract, lungs, or eyes. The most severe symptom of FNAIT is bleeding in the brain called intracranial hemorrhage (ICH), which can lead to lifelong brain damage or even death.
How do doctors diagnose FNAIT?
FNAIT is not routinely screened for during pregnancy. It is usually suspected if a baby is born with bleeding or bruising. Doctors may then order a blood test to determine the baby’s platelet count.
A final diagnosis can be reached by testing the mother’s blood for the presence of anti-HPA antibodies.
The diagnosis may further be supported by checking the genotype of the mother and the father to see which type of HPA they have and whether the two types are incompatible.
Doctors may also look at the baby’s brain with an ultrasound to see if there is any bleeding.
If a couple has had a previous baby affected by FNAIT and is expecting another, tests will be run during pregnancy to either diagnose or rule out FNAIT.
How is FNAIT treated?
A baby suspected of having FNAIT must be admitted to the neonatal intensive care unit to be closely monitored and receive treatment as needed to avoid or manage bleeding.
The primary treatment option is a platelet transfusion if the baby has a very low platelet count. This should be done before waiting for the results of the blood tests from the mother and the father to reduce the risk of ICH.
Intravenous immunoglobulin and/or corticosteroids may also be given to increase the platelet count, but there is not enough evidence to show these treatments are beneficial.
A platelet transfusion can also be done before the baby is born, but this is usually not advised due to the risk of inducing bleeding when performing the transfusion and the fact that this treatment must be repeated weekly.
Intravenous immunoglobulins and corticosteroids may also be given to a pregnant woman at high risk of having a baby with FNAIT to suppress her immune system and reduce the risk of the baby developing the disease.
Finally, two new experimental approaches are currently being tested to reduce the risk of FNAIT.
One of these is an antibody that competes with the antibodies of the mother in binding to the HPA of the baby without triggering their destruction.
The second, called nipocalimab, is a therapy currently being tested in a phase 3 clinical trial. The goal of the therapy is to reduce the levels of antibodies that attack the baby’s platelets in the mother.
