What is a Positive Antibody Screen in Pregnancy?

Why is knowing your blood type important in pregnancy?

Every human being has a blood type, the most common are A, B, AB, and O and Rh positive or negative. However, there are hundreds of other minor blood types that help our body determine whether the red blood cells (the cells that carry oxygen) in our blood stream are ours or foreign. 

When pregnant your doctor will draw prenatal labs that include checking your blood type and checking for antibodies against red blood cells. Antibodies are proteins that your body makes in order to fight off things it thinks don’t belong - like germs, bacteria, viruses or even your baby’s blood cells.  During pregnancy a small amount of your baby’s blood will enter your blood stream.

What does a Positive Antibody Test mean?

If you have a positive antibody screen, it means that your body has made antibodies that could attack your baby’s red blood cells. These antibodies can develop if:

• You’ve had a baby before with a different blood type than your own or your current baby’s blood type is different from yours (especially if you’re Rh-negative and your baby is Rh-positive).
• You’ve had a blood transfusion.

These antibodies can cross the placenta (the organ that connects you and your baby) and causes your baby to destroy its own red blood cells. This can cause anemia (not enough red blood cells to carry oxygen to the tissues/brain), which can make your baby very sick.

Is your baby at risk for anemia?

Ideally, we would want to know your baby’s blood type. Your baby’s blood type is determined by a combination of the mother and father’s blood types.

Attempting to determine your baby’s blood type

• Doctors may test the father's blood type to determine what blood types your baby will inherit, looking specifically for the blood types that you have an antibody to.
• Doctors may draw your blood to do specialized genetic testing to determine your baby's blood type. Although, this is very new and is not available for all antibodies.

In addition, your blood will be drawn to assess the level of antibodies in your blood to see if these levels are high enough to affect your baby.  

Lastly, your doctor will then assess your baby for anemia, based on the results of the above tests.

Monitoring your baby for anemia

Once it is determined that your baby is at risk for anemia, your baby will be monitored closely. A Maternal Fetal Medicine doctor will use ultrasounds to monitor for fetal anemia. You will have doppler ultrasound measurements of the fetal middle cerebral artery (MCA), an artery in the fetal brain that is sensitive for detecting fetal anemia. 

Treating your baby if they become anemic

If your baby shows signs of anemia, doctors might give your baby a blood transfusion while still in the womb, this is called an Intrauterine Transfusion (IUT). During this procedure, red blood cells are injected into your fetus through the umbilical cord. This procedure is done by a Maternal Fetal Medicine specialist with expertise in these cases, like the providers at CHI Health in Omaha. Intrauterine transfusions can help save your baby’s life with a success rate of over 97%.

If you have additional questions, reach out to your Women's Health provider.