Alloimmune Thrombocytopenia – What It Means for You and Your Baby
Overview
Alloimmune thrombocytopenia is a rare condition that can happen during pregnancy, sometimes even with the first baby. It occurs when a mother’s immune system mistakenly attacks her baby’s platelets—the part of the blood that helps stop bleeding.
If the baby has too few platelets, they are at risk of serious internal bleeding, including bleeding in the brain (stroke). This can lead to long-term damage or even death before or shortly after birth. The condition is very rare (about 1 in 1,200 births), but if it happens once, there’s a high chance (about 80%) it will happen again in future pregnancies—often more severely.
What Causes It?
The mother’s immune system makes antibodies that cross the placenta and attack the baby’s platelets, causing their levels to drop dangerously low. This makes it hard for the baby to stop bleeding if injured, and in severe cases, bleeding can happen inside the body—even in the brain.
When Do Doctors Suspect It?
It’s usually only discovered after a baby is born with signs like:
- Easy bruising
- Bleeding
- Very low platelet count
- Bleeding in the brain (seen with imaging)
Because it often has no signs during pregnancy, it’s hard to predict in a first-time mom. But if it happened in a previous pregnancy, doctors will test early in future pregnancies.
How Is It Diagnosed?
Special blood tests are done on both parents to see if there’s a mismatch in platelet types that could cause the mother’s body to attack the baby’s platelets.
In some cases, doctors may directly check the baby’s platelet type using one of these:
- Chorionic villus sampling (CVS)
- Amniocentesis
- Cordocentesis (drawing blood from the baby’s umbilical cord)
How Is It Treated?
Treatment is focused on protecting the baby by treating the mother during pregnancy. The most common medications used are:
- IVIG (Intravenous Immunoglobulin) – helps block the harmful antibodies
- Steroids (like prednisone) – to reduce immune activity
Sometimes doctors will check the baby’s blood in the womb to see how treatment is working.
Cesarean delivery is usually recommended to reduce the risk of bleeding during birth.
After birth, the baby may need treatments such as:
- Platelet transfusions
Exchange transfusions (to remove harmful antibodies)
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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