Pregnacy Rh Factor, Rh NEG Blood, and "Changing" Rh Factor

Q In my last two pregnancies my blood test results were that I have Rh- (Rh NEG) blood and received the antibody injections during pregnancy and after delivery. I am going to a different doctor for this baby, but the blood test came back stating that I am 0+ and that I am not Rh-.

How can my blood type change?
What dangers are involved if I receive the antibody while pregnant if I am not Rh-? (I was already given an injection in the first trimester because of bleeding.)
Is it possible for an Rh- blood type to switch by itself to Rh+?

A"Rh" another marker for types of blood, can be either Rh Negative or Rh Positive. If a patient with Rh Negative blood were to receive blood from a Rh Positive donor, she would make antibodies to the Rh Positive blood given to her. The same thing happens if she has a baby which, through inheritance from the father, would have Rh Positive blood, like the father. At the time of delivery when the placenta separates, there is some mixing of maternal and fetal blood. Some blood does get into the maternal bloodstream, and this is just like receiving a blood transfusion from a Rh Positive donor. The mother would then make antibodies to this Rh Positive blood. But since the mother is RH Negative, it's no big deal, because these antibodies will only attack Rh Positive blood, of which the mother has none.

Rh Positive and the next pregnancy.

If the next baby she's carrying is once again Rh Positive, then her old anti-Rh Positive antibodies, small enough to pass from her circulation through the filtering of the placenta into the baby's bloodstream, will attack the new baby's red blood cells.

Up to 15% of women have Rh Negative blood, but now we can give Rh Immune-globulin, big bulky anti-Rh Positive antibodies which fool the body into thinking the defense has already been launched. Therefore, no antibodies are made by the mother. And since these are bulky molecules, they won't pass on to the fetus. These "blocking" antibodies therefore protect the fetus.

Now that we have that out of the way, I can address your question.

No, it isn't possible to change blood types. But Rh Positive women are identified by their Rh Positive red blood cells. There is a very weak variant called the "Du" variant. It is actually an Rh Positive antigen, which would make a woman "Rh Positive," but since it is very weakly expressed in tests, it's possible to be mistakenly read as Rh Negative. Today, any Rh Negative woman should be tested further for the Du variant. If it's positive, then the blood type is corrected to Rh Positive, and no Rh Immune-globulin need be given.

If this is the case for you, then you received these shots for nothing with your previous pregnancies. Fear not, getting Rh immune-globulin when you're Rh Positive does no harm, except for your pocketbook. But before you go clobbering anyone on the head, do know that this is a recent test. So it may be that your new doctor has it right and that your previous doctors didn't have the technology back then to check for the Du variant.

Of course, it doesn't hurt to ask your doctor, just in case your blood tubes got mixed up with someone else's!

Although you didn't ask, I'll also tell you that if you were truly Rh Negative, you need the Rh immune-globulin even after a miscarriage or an ectopic pregnancy, since there can be mixing of maternal and fetal blood there too. We also give this shot to Rh Negative mothers who have undiagnosed bleeding during their pregnancy, car accidents, and version (converting a breech to a head-first baby).

A Controversy Pregnancy Treatment

Any women can be allergic to any medication, vaccine, or treatment given. It is possible that you can be allergic to the immune-globulin shot and you should ask your doctor about this possibility and what this may mean for you. Below is a response received about this article from one reader who was allergic. Please read her warning about her allergic reaction and then please read the response from a doctor who specializes in this field whose advice was sought upon receiving this letter.

Message From Reader:

I was reading stuff here on RH- mothers, etc. I just want to say that I am now 58 years old. When I was 22 I had an abortion and because I had A- du- blood they gave me a shot of Rhogam (? or Rhogram) and my lungs closed up so much I could not breathe and thought I was going to suffocate. By the next morning it was gone. Then when I was 24 I had another abortion and they wanted to give me that shot again and I told them not to do it. They tested it out on my arm. It swelled up bad. They told me if they gave it to me, it might kill me. When I was 28 I had a child and I told them about my reaction to their shot and they tested me and gave me something else. I was searching my blood type (A- du-)and ran into your website. I can't believe after all these years that people don't know that these shots can kill.--Michelle

Response From Doctor Who Specializes In This Pregnancy Field:

This is obviously a case of a single patient being allergic to the medication. AnyONE can be allergic to any ONE particular medication, vaccine, or treatment. However, just as one cannot discontinue all penicillin because some people, like me, are allergic to it, you cannot discontinue all vaccines, etc., with a rare unfortunate event like this.

RhoGam has reduced the disastrous incidence of fetal disease--hemolytic disease of the newborn--and fetal death a thousand-fold. "Michelle" is a single untoward reaction, albeit a severe one. She's correct that this vaccine can kill her and is correct to refuse it (as I have to do with penicillin). One is wise to refuse anything one is allergic to--in her case, an anaphylactic reaction. But thousands of babies every year who would be otherwise dead, handicapped, or retarded are born healthy due to this miraculous breakthrough in medicine.