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Rh Blood Group, Rh Factor & Erythroblastosis Fetalis

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  • 0:05 Blood Groups
  • 0:50 Rh Blood Group System
  • 1:44 Rh-Negative Blood
  • 3:24 Erythroblastosis Fetalis
  • 5:37 Lesson Summary
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Lesson Transcript
Instructor: Rebecca Gillaspy

Dr. Gillaspy has taught health science at University of Phoenix and Ashford University and has a degree from Palmer College of Chiropractic.

Rh factor is a red blood cell antigen found in most people. Those with Rh factor are Rh positive, while those without are Rh negative. In this lesson you will learn about Rh blood compatibility and its importance during pregnancy.

Blood Groups

Antigens on the outside of your red blood cells determine your blood type
Antigens

We previously learned that your red blood cells have tiny antigens attached to them, and it is these antigens that determine your blood type. For example, if your red blood cells have A antigens, then you will have type A blood. If your red blood cells have B antigens, you will have type B blood. If your red blood cells have both A and B antigens, then your blood type is said to be AB. And if your red blood cells contain no antigens, then you have type O blood. But A and B antigens are not the only antigens found on your red blood cells; you also have an antigen called the Rh factor. In this lesson, we will take a look at the Rh factor and the significant role it can play during pregnancy.

Rh Blood Group System

The Rh factor is simply a red blood cell antigen - just like the A antigen and the B antigen that are used to determine your blood type. The Rh factor is named after the Rhesus monkey, which is the animal where it was first identified. The Rh factor is important when we learn about the Rh blood group system. The Rh blood group system is a classification system for blood that depends on the presence or absence of the Rh antigen - or factor - on your red blood cells. In other words, you were either born with the Rh factors on your red blood cells, like most people, or you were born without them, which is more rare, but significant as we will learn in this lesson. Since the Rh factor can be either present (+) or absent (-), we refer to people as being either Rh positive if they have the Rh factor, or Rh negative if they do not.

Rh Negative Blood

The presence or absence of the Rh factor determines whether you are Rh positive or Rh negative
Rh Blood Group System

We previously learned that in the ABO blood group system that antibodies are automatically produced based on antigens not present on your red blood cells. So you might think that the Rh blood group would be the same way and assume that if you are born without the Rh antigen that your body would automatically make antibodies against it. However, in the Rh blood group system, the antibodies are not automatically produced. Instead, a person with Rh negative blood needs to be 'sensitized' before he or she will start to produce antibodies to the Rh antigen. Let's look at an example.

If you have a woman with Rh negative blood who has never had a blood transfusion or any other exposure to anyone else's blood, she will not have any antibodies against the Rh antigen. It's almost like her body doesn't even care which Rh blood group she belongs to. However, if this woman gets a bad blood transfusion that contains Rh positive blood, her body will now be 'primed,' or 'sensitized,' to the Rh positive antigen and start to produce anti-Rh positive antibodies. Because this was the first exposure, there's no real harm done, other than the fact that now she has the antibodies floating around in her bloodstream. The only significant point is that because the antibodies are now in her bloodstream, she can never again come in contact with Rh positive blood or her antibodies will attack. It's almost like she gets a free pass for her first exposure to the wrong blood type when you talk about Rh factor. However, this first exposure sets you up for problems if you ever get the wrong blood again.

Erythroblastosis Fetalis

Now, let's consider a different woman. Let's say that she is a pregnant Rh negative woman who is carrying an Rh positive child. During pregnancy, and especially during delivery, there is a good chance that the child's Rh positive blood can pass through the placenta and into the mother's bloodstream - somewhat like the blood transfusion we talked about earlier. What is going to happen to that first child? Well, the answer is nothing. In fact, the first pregnancy for an Rh negative mom and an Rh positive child typically results in a healthy baby. But, the mother is now sensitized by Rh positive antigens that have passed through the placenta and into her bloodstream. That means she will start to form anti-Rh positive antibodies. This will be a problem if she ever becomes pregnant again with an Rh positive child, because her antibodies will reject the child.

Someone with Rh negative blood needs to be exposed to Rh positive blood to produce antibodies
Rh Antibodies

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