When Do You Test for Rh Factor in Pregnancy? We Answer Your FAQs

If you’re in the 1st trimester of pregnancy or planning to become pregnant soon, you’re likely already thinking about the tests and screenings you’ll undergo. One of the most important involves Rh factor and pregnancy. A routine blood test performed during early prenatal care, an Rh factor screening helps identify potential blood type incompatibilities that could affect your baby. 

In this article, we’ll help you understand what this test is and why it matters, how Rh incompatibility issues can be prevented and when you should test for Rh factor in pregnancy. 

At Chapel Hill OBGYN, we’ve been providing expert care and treatment to women in the Triangle area for over 50 years. If you’re newly pregnant or planning to become pregnant soon, we invite you to contact us for an appointment. We would love to be your trusted partner throughout every step of your prenatal journey and beyond. 

What is an Rh Factor and Why Does It Matter During Pregnancy?

The Rh (Rhesus) factor is a protein found on the surface of red blood cells. If your blood cells have this protein, you’re Rh-positive; if your blood cells don’t have this protein, you’re Rh-negative. 

While the Rh-negative blood type is rare, being Rh-negative on its own is not a medical condition and does not impact your everyday health.   

The Rh factor matters during pregnancy because problems can occur if you are Rh-negative and your baby is Rh-positive. Your baby can inherit either parent’s Rh status, so if your partner is Rh-positive, your baby may inherit that trait. 

How Does Rh Incompatibility Impact a Pregnancy?

Rh incompatibility occurs when your blood type is Rh-negative and your baby’s is Rh-positive. 

Though your blood and your baby’s blood are usually separated, in some cases, a small amount of fetal blood cells may enter your bloodstream during pregnancy, delivery or certain medical procedures. 

If this happens, your Rh-negative immune system may identify those Rh-positive blood cells as invaders and produce antibodies against them.

This immune response is known as Rh sensitization. The first pregnancy in which sensitization occurs is usually unaffected, but you may already be sensitized from a prior pregnancy, a pregnancy loss, a procedure or a blood transfusion.

Future pregnancies can be affected if you conceive another Rh-positive baby because those antibodies remain in your body and may cross the placenta and attack your baby’s red blood cells.

If left untreated, Rh antibodies can create potential complications for your baby, such as fetal anemia, heart failure, and hydrops fetalis, a serious, life-threatening condition involving fluid accumulation. 

Can Rh Incompatibility Issues Be Prevented?

The good news is that Rh incompatibility can often be prevented with treatment. 

A medication called Rh immune globulin (RhIg), commonly known by the brand name RhoGAM®, helps deter sensitization by preventing your immune system from creating antibodies against Rh-positive blood cells. 

We may recommend RhIg:

• Around the third trimester (usually at around 28 weeks)
• After delivery if your baby is Rh-positive
• After events that may increase the likelihood of fetal Rh-positive red blood cells entering your Rh-negative bloodstream, such as:
  • Miscarriage, depending on gestational age, the circumstances of the loss and other factors
  • Ectopic pregnancy 
  • Abdominal trauma
  • Trauma, such as car accidents and falls
  • Vaginal bleeding during pregnancy
  • Prenatal tests like amniocentesis, chorionic villus sampling (CVS) or other fetal procedures 

This preventive treatment is highly effective when given at the appropriate time. It’s important to attend your prenatal appointments and follow care recommendations and testing schedules to help support the best possible outcome. 

While RhIg can help prevent antibody formation in an unsensitized Rh-negative patient, it cannot reverse existing sensitization. In that case, additional monitoring may be required.

When Do You Test for Rh Factor During Pregnancy?

Rh factor testing, a simple blood draw that determines your blood type and Rh status, is one of the routine blood tests you’ll receive early in prenatal care, typically during your first prenatal visit. 

You’ll also receive an antibody screening test to determine whether your immune system has already produced Rh antibodies that might attack your baby’s blood cells.

This information helps us determine whether Rh incompatibility could become a concern during your pregnancy. 

What happens after testing depends on your results.

• If you are Rh positive, routine prenatal care generally continues. 
• If you are Rh negative, we’ll develop a personalized monitoring and prevention plan based on your circumstances. You’ll receive RhIg treatment at around 28 weeks. 
• When your baby is Rh-positive and you have not already been sensitized, you’ll receive RhIg within 72 hours after delivery. 

Testing early in pregnancy, followed by routine monitoring and preventive treatment, can help protect your baby throughout your pregnancy. Most women with Rh incompatibility go on to have healthy pregnancies and deliver healthy babies.

Chapel Hill OBGYN: We’re Your Partner for Expert, Personalized Prenatal Care

Understanding Rh factor and pregnancy is an important part of protecting your health and your baby’s well-being. The good news is that early testing and preventive treatment can significantly reduce the risks associated with Rh incompatibility. 

At Chapel Hill OBGYN, we offer comprehensive prenatal care, including early Rh factor and other testing, routine screenings and personalized guidance throughout every stage of your pregnancy journey and beyond.

If you are newly pregnant or planning a pregnancy, we encourage you to schedule an appointment with us so you can receive the expert prenatal care and support you deserve.