Why Doctors Test for Rh Factor During Pregnancy

An Rh test can determine whether you have Rh-positive or Rh-negative blood. Read on to learn why testing for Rh factor is important during pregnancy.

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The Rh factor test is a routine test during pregnancy. It's usually conducted when your blood sample is taken during your first prenatal care visit. The results will determine if your blood has "Rh factor"—a protein on the surface of red blood cells. If your blood type is positive (for example, A positive or O positive), you have the Rh factor; if it's negative, you do not.

According to the American Red Cross, most people are Rh-positive. The Rh factor is genetic, meaning it is passed from parent to child through genes. But not all fetuses share the same Rh factor status as their gestational parent. When this occurs, it's called Rh-incompatibility because it can cause complications.

Read on to learn why the Rh factor test is important and how the results could impact your pregnancy.

What Is Rh Incompatibility?

Health care providers check for the Rh factor during pregnancy because incompatibilities between you and your fetus could result in complications. If you are Rh-positive, you're in the clear; Rh-positivity won't affect you or your baby. On the other hand, if you're Rh-negative and your fetus is Rh-positive, it could result in problems.

With Rh incompatibility, your body will consider the baby's Rh factor a foreign object if your blood and your baby's blood interact. This interaction is rare, but according to the American College of Obstetricians and Gynecologists (ACOG), it can occur during childbirth and in some other circumstances, including:

When this occurs, your body produces antibodies that attack the baby's blood cells. These antibodies can lead to anemia, which is dangerous for a fetus because fetal blood cells may be destroyed faster than they can be reproduced, potentially causing newborn jaundice and even fetal death.

Thankfully, early detection of Rh factor incompatibility problems can dramatically reduce these dangers. So it's vital to get tested early in your pregnancy.

How to Test for Rh Type

Rh-type is determined through a simple blood test. To perform the test, a phlebotomist or nurse will take your blood through a small needle, usually from a vein in the arm. The sample is then sent to a lab for analysis.

This test is typically done early in pregnancy, often during the first prenatal exam. Test results are available within a few days. You probably won't need to take any measures if you are Rh-positive (Rh factor is present).

Treatment for Rh-Negativity

If your blood sample reveals that the Rh factor is not present, you are considered Rh-negative. When you are Rh-negative, your health care provider will follow up with several steps to ensure you do not make antibodies against your fetus's blood.

Rh antibodies, when made, are permanent. That means they may impact not only your current pregnancy but future ones, too. So, preventing antibodies is critical.

Blood test to check for antibodies

First, your blood will be retaken at 28 weeks for testing. This test will check to confirm that you are not making antibodies. In addition, the blood test will reveal how many antibodies you've already made if antibodies are present.

If antibodies are detected, your baby will be closely monitored for the rest of your pregnancy. If antibody levels become too high, special measures may be taken, including blood transfusions to the baby and early delivery.

Medication to prevent antibodies

If you don't have antibodies, you'll be given an injection of Rh-immunoglobulin (brand name RhoGAM). This medication prevents your body from producing antibodies against your baby's Rh factor, protecting your baby and any future pregnancies from harm. Since childbirth is the most significant risk of blood interaction, if your baby is found to be Rh-positive, you'll be given another injection of RhoGAM 72 hours after the birth.

While RhoGAM protects you from developing permanent antibodies, which can protect current and future pregnancies, it is only effective for the pregnancy in which it is administered. As a result, you will need to repeat the doses in any subsequent pregnancies.

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