vials of blood lying on medical forms

Rh factor during pregnancy: why you should know it

What is the Rh Factor?

There are four blood types—A, B, AB or O. Each blood type is either positive or negative for the RH antigen, a protein on the surface of the red blood cells in your blood. A plus or minus sign after A, B, AB, or O tells you what Rh factor you have. For example, some people are A negative, while some are A positive. 

While most people have a positive Rh factor, about 15% of the population is Rh-negative, meaning they do not have the antigen. The Rh factor doesn’t cause health problems in any way. It becomes important when blood types are mixed, such as when a person is pregnant or giving birth. 

If you are Rh-negative and the fetus is Rh-positive, which is possible if your partner is Rh-positive, the fetus is at risk of developing Erythroblastosis Fetalis, also known as Rh incompatibility. This is a complication where antibodies made by the Rh-negative mother attack the fetus’s red blood cells. This results in blood cells being destroyed, which causes levels of bilirubin to rise and can be dangerous.

Prevention and dosing

Rh incompatibility can be prevented with the use of RhoGAM shots, which are typically given between 26 and 28 weeks of pregnancy. If your baby is found to be Rh-positive at birth, you will receive an additional dose within 72 hours after giving birth. Your doctor will determine the appropriate dose of RhoGAM after delivery.

RhoGAM should also be given after the following instances:

  • After abdominal trauma
  • Any invasive procedures such as amniocentesis, chorionic villus sampling or percutaneous umbilical blood sampling
  • Maternal or fetal bleeding during pregnancy
  • Ectopic pregnancy (pregnancy in which the fertilized egg implants outside the uterus). 
  • RhoGAM should also be considered after a threatened pregnancy loss or pregnancy termination. 

The dose and dosing schedule will be determined by your doctor.

How does RhoGAM work?

RhoGAM contains antibodies specific to the Rh protein. These antibodies coat the Rh protein on any fetal blood cells that have entered the pregnant person’s bloodstream. This and other mechanisms prevent the pregnant person’s immune system from reacting to fetal Rh protein and developing their own antibodies, which could endanger a future pregnancy. Therefore, prevention remains the best treatment. 

How is Rh Incompatibility treated?

Treatment of an infant who is already affected depends on the severity of the condition.

Infants with mild Rh incompatibility may be treated with phototherapy using bilirubin lights. IV immune globulin may also be used. For infants severely affected, an exchange transfusion of blood (when the patient’s blood is removed and replaced by donated blood or blood components) may be needed. This is to decrease the levels of bilirubin in the blood.

Being aware of your blood and Rh type during pregnancy can help you partner with your medical team to get the best preventative treatment needed for you and your baby. Although it can be scary, know that you’re not alone in managing this common condition and that prevention is very successful.

You can determine if you are positive or negative for the Rh factor with a routine blood test at your first prenatal healthcare provider’s appointment.

Read more
  • “The Rh Factor: How It Can Affect Your Pregnancy: FAQ027.” ACOG. American College of Obstetricians and Gynecologists, 9/13/2015. Web.
  • “What Is Rh Incompatibility?” National Heart, Lung, and Blood Institute. U.S. Department of Health & Human Services, 1/1/2011. Web.
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