The significance of being Rh Negative or Rh Positive

Although we have become accustomed to adding a positive or negative description to our blood type, the Rh factor plays a larger role than many of us realize. Knowing your blood type can play a significant role in your life and health.

In 1937, Karl Landsteiner and Alexander Weiner discovered a new blood type: the rhesus blood type, or Rh factor. The rhesus protein is named for the rhesus monkey, which also carries the gene, and is a protein that lives on the surface of the red blood cells. This protein is also often called the D antigen. When it comes to blood transfusion, anyone who is Rh positive can receive blood from someone who is Rh negative, but those with negative blood types cannot receive from anyone with a positive blood type.

To put it simply, Landsteiner and Weiner discovered that blood types can be either Rh positive or Rh negative, doubling the commonly known blood types from four (A, B, AB, and O), to the eight we know today.

However, when it comes to the Rh blood types, many of us do not fully understand what it means to be positive or negative. In the United States, approximately 85% of the population has an Rh-positive blood type, leaving only 15% with Rh negative. Just as we inherit our blood type “letter” from our parents, we inherit the Rh factor from them as well. Each person has two Rh factors in their genetics, one from each parent. The only way for someone to have a negative blood type is for both parents to have at least one negative factor. For example, if someone’s Rh factors are both positive, it is not possible for his or her child to have a negative blood type. Only people with at least one Rh-negative factors will have a negative blood type, which is why the occurrence of Rh-negative blood is less common than Rh-positive blood.

When Landsteiner and Weiner discovered the Rh protein, they were researching solutions for the cause of a medical mystery that killed dozens of babies each day. This led to the development and FDA-approval of RhoGAM® in 1968. RhoGAM, or Rho(d) Immune Globulin Human, is a sterilized solution made from human blood. It is used to prevent an immune response in mothers who are Rh negative. If a pregnant woman who is Rh negative does not receive RhoGAM, and is carrying an Rh-positive baby, she risks the health of future pregnancies because she has been exposed to the positive blood from her current unborn baby.

Once a woman finds out she is pregnant, her doctor will test her blood to determine her Rh factor. Since more people are Rh positive than Rh negative, it is likely that an Rh-negative mother could be carrying a baby who is Rh positive, creating the risk for hemolytic disease of a newborn (HDN) in future pregnancies, essentially destroying that baby’s red blood cells. If a woman is Rh negative, she will most likely receive a RhoGAM injection.

When a woman receives RhoGAM, it protects her immune system from the exposure to the current baby’s Rh-positive blood. If she does not receive the injection, her body will develop antibodies that could attack the positive red blood cells of babies in subsequent pregnancies, which will cause HDN. HDN can cause serious illnesses, brain damage or even death in a fetus or newborn. Pregnant women typically receive RhoGAM twice during their pregnancy: once at approximately 28 weeks and once within 72 hours of delivery, if in fact, the newborn baby is Rh positive.