There are two rare blood disorders that can occur in pregnancy that are quite similar: fetal and neonatal alloimmune thrombocytopenia (FNAIT) and hemolytic disease of the fetus and newborn (HDFN).
FNAIT is caused by a genetic mismatch between mother and fetus of human platelet antigens (HPAs). HDFN is caused by an incompatibility between mother and fetus of blood type–most often due to Rh blood factor incompatibility (negative or positive), triggered by the D antigen, or less commonly ABO blood group incompatibility.
Both conditions are potentially serious, as the mother’s immune system produces antibodies that cross the placenta and destroy the fetus’s red blood cells, in HDFN, and blood platelets, in FNAIT. Another similarity lies in the fact that it has been shown that ABO incompatibility can also play a role in the occurrence of FNAIT.
What is FNAIT?
FNAIT is a rare autoimmune disease that can affect the blood platelets of the fetus. It occurs when the mother and baby have mismatched human platelet antigens (HPA), as a result of the fetus inheriting a HPA from its father not present in its mother. If the mother is exposed to the fetus’s blood during pregnancy or delivery, her immune system develops antibodies to attack and break down the fetus’s blood platelets. This is dangerous for the baby, causing a low platelet count and bleeding that doesn’t clot. It can lead to bleeding in the brain and internal organs, and fetal death if undetected and untreated.
In newborns, symptoms of FNAIT include bruising, skin discoloration and more seriously, intracranial hemorrhage (ICH). In newborns suspected of FNAIT, urgent treatment of the condition is required to avert long-term neurological damage and death.
Blood type incompatibility in FNAIT
FNAIT can be caused by ABO incompatibility in rare cases. Human platelets carry A and B blood group antigens on their surface and an unusually high level of ABO antibodies in the mother can lead to the destruction of platelets in newborns, leading to FNAIT. In particular, a type O+ mother with an ABO incompatible fetus can develop antibodies that cross the placenta and can target both red blood cells and platelets.
During pregnancy, FNAIT can be difficult to treat, with intravenous immunoglobulin (IVIG) and steroids used to increase platelet levels before delivery. In newborns, the treatment of choice for FNAIT remains platelet transfusion, sourced from donors or from the mother, with the addition of IVIG to help neutralize the maternal antibodies.
