While fetal and neonatal alloimmune thrombocytopenia (FNAITFetal and neonatal alloimmune thrombocytopenia A rare condition in which a mother’s immune system attacks fetal platelets, leading to dangerously low platelet levels before and/or after birth.) can occur in first pregnancies, it may only be diagnosed postnatally. In subsequent pregnancies, the fetus is likely to be more severely affected by the already existing maternal antibodies that can cross the placenta from as early as 16 weeks’ gestation and progressively break down fetal platelets.
What is HDFN?
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.
FNAIT in first pregnancies
FNAIT is often compared to hemolytic disease of the fetus and newborn (HDFN) as they are both rare blood disorders where the alloimmunized pregnant mother’s antibodies attack the fetus. In HDFN, fetal red blood cells are destroyed leading to anemia and in FNAIT, fetal platelets are destroyed leading to thrombocytopeniaThrombocytopenia A platelet count that is lower than normal.. However, unlike in HDFN, which most often occurs in subsequent pregnancies, FNAIT occurs in almost 50% of first pregnancies.
Learn more about FNAIT signs and symptoms
There is no standard prenatal screening for FNAIT. If it is diagnosed during the pregnancy, it is as the result of testing performed due to family medical history, or if fetal hemorrhageFetal hemorrhage Any bleeding that occurs before birth. In FNAIT, this usually results from extremely low platelet counts. is detected by ultrasound.
It is usually diagnosed following delivery, in cases where the neonate shows bruising, or bleeding under the skin known as petechiae or purpura – small red or purple spots on the skin. A low platelet countPlatelet count A measure of how many platelets are in the blood. FNAIT is characterized by severely reduced counts in a fetus or newborn. can also be detected in a blood test. Severe bruising or hematomas may also occur.
Symptoms in first pregnancies are generally mild and if there is no serious bleeding, a platelet transfusionPlatelet transfusion A treatment for newborns with very low platelet counts that ideally uses HPA-compatible or washed maternal platelets. is usually effective in treating FNAIT, with no long-term consequences.
FNAIT in subsequent pregnancies
Diagnosis of FNAIT following a first pregnancy informs the prenatal care of all subsequent pregnancies as it has a 90% chance of recurring. As the maternal antibodies against the inherited fetal antigens already exist, the risk is that fetal platelets will be attacked early in the pregnancy, with potentially life-threatening consequences. There is also a greater risk of miscarriage. In addition to close monitoring by ultrasound and blood tests throughout pregnancy, noninvasive treatment options of maternal intravenous immunoglobulin (IVIG) and steroids are administered as preventative measures. IVIGIntravenous immunoglobulin A treatment given to pregnant women with a history of FNAIT or known alloantibodies. IVIG reduces the immune reaction against fetal platelets. and steroids have been shown to prevent severe thrombocytopeniaSevere thrombocytopenia A dangerously low platelet count, typically below 50,000 platelets per microliter and sometimes far lower in FNAIT. in the fetus.
Invasive treatment such as serial intrauterine platelet transfusions (IUPT) is generally avoided due to the risk of bleeding and hemorrhaging, and potential miscarriage.
The greatest risk to fetuses and newborns with FNAIT is an intracranial hemorrhageBrain bleed Bleeding inside the fetal brain, also known as an intracranial hemorrhage. In FNAIT, it's often caused by severe thrombocytopenia and can lead to long-term disability or death. (ICH). If it occurs in previous pregnancies, there is a high risk that it will be present in subsequent pregnancies.
If ICH is suspected, an early delivery–often by cesarean–is the only way to effectively treat it.
