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Pregnancy and Rh Sensitization

What is Rh factor? First: Yikes! What kind of question is that? Am I back in school in a science class? Is it chemistry? Biology? And what does it have to do with pregnancy? Life and science do intersect, don’t they? And sometimes in important ways. So here’s some information about this intersection as it may relate to your pregnancy.

Before we get into Rh detail, let us add that besides this scientific question, you may have plenty of other questions – especially if you just found out (or suspect) you may be unexpectedly pregnant. Avenue Women’s Center is here to assist you with not only objective, factual questions, but also to help you work through some of the more difficult, subjective questions about an unplanned pregnancy… the ones that only you can answer. If this is a time when you could use some support in this, we hope you will call us for a private, confidential pregnancy consultation.

If you have ever had your blood type identified medically, you know your blood is in one of the following categories: A, B, AB, or O. After the identifying letter, there is also a (+) or (-). Most simply defined, Rh factor is about the (+) or (-). It refers to a type of protein on the surface of red blood cells. This particular protein can cause a response from the immune system.

People who have the Rh factor protein are identified as Rh-positive. If you do not have the protein, you are Rh-negative. Most people—about 85% of the population—inherit the Rh factor, and are Rh positive. Just 15% of people do not have this protein in their blood, and are Rh-negative.

How is Rh factor important for pregnancy? A routine part of an early pregnancy check up will include having blood tested for Rh factor. As noted earlier, most people are Rh positive.

  • If you test Rh positive, there is no potential problem of blood incompatibility with the fetus. A pregnant woman’s Rh positive blood will not interact with the blood of the fetus in any harmful way. Remember, it’s about a potential immune system response; this will not happen if your blood is Rh positive. For an Rh positive woman, no action is needed.
  • If you are Rh negative, additional steps will be taken. It is possible that your partner will be tested to determine whether his blood is Rh positive or negative. This testing is not practical in many situations. Regardless of a partner’s status, medical providers are able to offer safe care.
  • If the man, too, is Rh negative, the fetus would also be Rh negative. Being the same in Rh factor, your body would not identify the fetus as “foreign.” No immune response would be triggered, and there would be no danger of Rh incompatibility in the blood.
  • The only potential concern is if the woman is Rh negative and the man is Rh positive.
  • If your partner’s blood is Rh positive, the fetus could be either Rh positive or negative. If you are Rh negative and the fetus inherits the positive Rh factor from him, there may be an incompatibility between your blood and that of the fetus. Your body, recognizing the fetal blood type to be different from yours, may produce antibodies to “protect” you from what it sees to be “foreign.” This response of an immune system is called Rh sensitization.

What is the impact of an incompatibility in a first pregnancy? An incompatibility will usually not be a problem. The woman will not yet have antibodies that would respond negatively to the fetal Rh factor. A shot of Rh immunoglobulin (Rhlg) can be given that will prevent antibodies from being produced, regardless of whether the pregnancy ends with a delivery, induced abortion, or miscarriage.

What is the impact in a subsequent pregnancy? If a woman’s earlier pregnancy (whether delivery, induced abortion, or miscarriage) generated antibodies, they remain in her system. This could become a concern if she became pregnant again with another Rh positive fetus. Potentially, the antibodies could cross the placenta and attack the red blood cells of the fetus. Your medical provider can provide a blood test called an “antibody screen” to assess whether antibodies have developed. If the screening test reveals that you are Rh sensitized and antibodies have developed, testing may be done to determine the Rh factor of the fetus. If it is confirmed that blood types are compatible (both negative), no treatment will be necessary. If incompatible with your negative Rh factor, the pregnancy can be monitored and action may be taken as indicated.

What do I need to know? This article has provided some general information about Rh sensitization. We understand that you may have heard about Rh factor, and be starting to search for facts. We encourage you to talk with your medical professional. S/he is the person who will be able to best address your questions and concerns about your Rh situation. We find that many questions that seem overwhelming at first can be easily overcome once you have the right care on your side.

And that is a key reason why Avenue Women’s Center exists. When a woman is beginning to face the reality of an unplanned pregnancy… when concerns are beginning to press in… when “it’s just not the right time” and setting a positive direction feels overwhelming… we are here for you. For a free, private pregnancy consultation at one of our four Chicagoland locations, please contact us by phone, text, email, or chat.


  • American College of Obstetricians and Gynecologists. (2013, September). The Rh Factor: How It Can Affect Your Pregnancy. Retrieved from:
  • Web MD. Rh Sensitization During Pregnancy – Topic Overview. Retrieved from:
  • What to Expect. (2017, March). Rh Factor Testing. Retrieved from:
  • Mayo Clinic. (2015, June). Tests and Procedures: Rh factor blood test. Retrieved from:
  • Medical Discoveries. Rh factor. Retrieved from:

Reviewed by Patricia Kuenzi, APN-CNP, MSN, ANP, PNP.

The information provided here is general in nature.  It is not a substitute for a consultation with a medical professional. Before any medical procedure, it is imperative that you discuss your personal medical history, risks, and concerns with your doctor. If you have questions during or after a procedure, your doctor should be immediately contacted. Avenue Women’s Center is not an emergency center.  If you are experiencing severe symptoms, such as bleeding and/or pain, seek immediate medical attention.  Contact your physician, go to an emergency room, or call 911.