Severe alloimmune thrombocytopenia occurs in about 1 in 1,200 births. This condition may affect the first pregnancy. It is usually never anticipated until a mother has an affected infant. The recurrence risk is about 80%, with subsequent pregnancies usually more seriously affected. The risk to the baby may be significant. Intracranial hemorrhage (stroke) may occur in about 10-20% of cases. There is also an increased risk of death of the baby while in the womb or after birth.
Alloimmune thrombocytopenia is an immune mediated process in which antibodies produced by the mother crosses the placenta and enters the fetal circulation and attack the fetal platelets. This can result in a very low platelet count in the baby. Platelets are the component of blood that are required to make blood clots. When the platelet count drops too low (thrombocytopenia), then the baby can develop a bleeding disorder. The baby will then have an increased propensity to bleed. The most catastrophic site of bleeding is in the baby’s head, causing hemorrhagic stroke.
Alloimmune thrombocytopenia is usually suspected if a prior child was born with a very low platelet count (thrombocytopenia), bruises, bleeding from various sites, or an intracranial hemorrhage. Sophisticated laboratory testing using blood from both the mother and the father must be done in specialized laboratories to confirm the diagnosis.
The first step in caring for a couple with suspected alloimmune thrombocytopenia is to determine if the baby is at risk. Both the mother and father’s blood should be tested to determine the exact nature of the platelet incompatibility. The BloodCenter of Wisconsin Platelet and Neutrophil Immunology Laboratory is the recognized national leader in performing these blood tests. The baby can also be checked directly; fetal platelet antigen status via DNA analysis can be done from chorionic villi sampling (CVS), amniocentesis, or cordocentesis. Maternal antibody titers do not accurately reflect presence or severity of this disease.
Treatment of alloimmune thrombocytopenia is individualized. Studies have shown that certain factors that may have affected a prior baby may be important to determine the level of risk in the subsequent pregnancy. Thus, it is very important to get as much information from the prior pregnancy as possible. Current treatment strategies focus predominantly on medical therapy. This means that medicines are given to the mother. Current treatment regimens include intravenous immunoglobulin (IVIG) and/or prednisone. Fetal blood sampling to assess the baby’s platelet count while still in the womb may be necessary to gauge treatment success. Cesarean delivery is recommended. After birth, the baby usually will require further treatments, including platelet and exchange transfusions.
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