Once a woman finds out she is pregnant, her doctor will test her blood to determine her Rh factor. 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. It is used to prevent an immune response in mothers who are Rh negative. RhoGAM, or Rho(d) Immune Globulin Human, is a sterilized solution made from human blood. This led to the development and FDA-approval of RhoGAM® in 1968. 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. 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. 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. The only way for someone to have a negative blood type is for both parents to have at least one negative factor.

Each person has two Rh factors in their genetics, one from each parent. Just as we inherit our blood type “letter” from our parents, we inherit the Rh factor from them as well. In the United States, approximately 85% of the population has an Rh-positive blood type, leaving only 15% with Rh negative. However, when it comes to the Rh blood types, many of us do not fully understand what it means to be positive or negative. 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. 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. This protein is also often called the D antigen. 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. In 1937, Karl Landsteiner and Alexander Weiner discovered a new blood type: the rhesus blood type, or Rh factor.

Knowing your blood type can play a significant role in your life and health. 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.

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