What is Maternal Alloimmunization?
Alloimmunization, often called Rh-isoimmunization or Rh incompatibility was first described in Rh negative women with an Rh-positive fetus, but it can occur with many other blood type incompatibilities. It is a condition that may occur during pregnancy when there is an incompatibility between your blood type and your baby’s blood type. During pregnancy, red blood cells from your unborn baby can cross into your bloodstream through the placenta. If your blood type is different than your baby’s, your immune system may treat the baby’s blood cells as if they were a foreign substance and produce antibodies against them. Those antibodies can cross back through the placenta and attack your baby’s red blood cells. This is called hemolytic disease of the fetus, a condition in which red blood cells are destroyed faster than the body can replace them. Without enough red blood cells, your baby won’t get enough oxygen.
If hemolytic disease is left untreated it may lead to serious problems, such as brain damage; hydrops fetalis (**LINK**) (abnormal amounts of fluid build-up in two or more body areas); seizures; problems with mental function, movement, hearing and speech, or even death.
Alloimmunization does not usually cause problems during a first pregnancy because the baby often is born before many of the antibodies develop. However, once the antibodies have formed, your body does not get rid of them, so any subsequent babies are more likely to have problems if they have the same blood type as the first baby.
How is Alloimmunization diagnosed?
All mothers are tested for the development of antibodies three times during pregnancy: at their first prenatal visit, at 28 weeks’ gestation, and at delivery. If there is Alloimmunization during your pregnancy, it is important that you and your fetus be evaluated by a Maternal-Fetal Medicine specialist for hemolytic disease of the fetus. If your newborn has hemolytic disease he/she should be evaluated by a Neonatologist. Symptoms of hemolytic disease in your fetus or newborn may include:
- An abnormally large amount of amniotic fluid
- Jaundice (yellowing of the skin and eyes)
- Decreased muscle tone
- Signs of red blood cell destruction in your baby’s blood
If your doctor suspects Alloimmunization, testing will confirm the diagnosis. Common tests for diagnosing Alloimmunization include:
- A blood test to detect antibodies that are stuck to the surface of red blood cells (known as a direct Coombs test)
- Testing of either or both the father of the baby or the fetus by amniocentesis to determine the fetus’ blood type
- Ultrasound examination of the blood flow velocity in the fetal brain
- Directly testing the fetal blood type and blood count by cordocentesis
- A blood test to look for higher-than-normal levels of bilirubin in your baby’s umbilical cord blood
Can Alloimmunization be prevented?
Rh-isoimmunization (incompatibility to the Rh blood type) is preventable, and prevention is preferable to treatment. Rh negative women are given injections of a medicine called Rh immune globulin (RhoGAM) to keep their body from making Rh antibodies. If you have Rh-negative blood, you’ll need this medication every time you are pregnant with a baby with Rh-positive blood. There are certain events (for example miscarriage, or chorionic villus sampling) expose you to Rh-positive blood, and could therefore affect your unborn child. If you are treated with Rh immune globulin immediately after one of these events, you may be able to avoid Rh incompatibility during your pregnancy.
How is Maternal Alloimmunization treated?
If there is severe hemolytic disease of the fetus, then a Maternal-Fetal Medicine specialist can give your fetus in-utero transfusions. These can be lifesaving and prevent many of the complications of hemolytic disease.
After delivery, if your baby has a mild case of hemolytic disease your doctor may treat the condition with phototherapy (light therapy). In some cases, your baby may also need one or more blood transfusions.