Important: This page is general information, not medical advice. It does not recommend or prescribe any treatment. Always consult your doctor or pharmacist before starting, stopping or changing any medicine.
About Rh Incompatibility
There are four major blood types: A, B, O, and AB. The types are based on substances found on your blood cells. Your blood type also has a positive or negative sign. This is called Rh factor, which is a protein. If your blood cells have this protein, you are Rh-positive. If you don't, you are Rh-negative.
Rh factor is inherited (passed down through families). Most people are Rh-positive, meaning they have the Rh factor. Rh-negative people don't have it. Being Rh-negative doesn't affect your health, but it can affect the health of your fetus if you are pregnant.
If you are pregnant and are Rh-negative and your fetus is Rh-positive, it's called Rh incompatibility. Blood from your fetus can cross into your bloodstream, especially during childbirth. If you're Rh-negative and your baby is Rh-positive, your body will react to the fetus's blood as a foreign substance. It will create antibodies (proteins) that can damage their red blood cells.
These antibodies usually don't cause problems during your first pregnancy. But Rh incompatibility may cause problems in later pregnancies if the fetus is Rh-positive. This is because the antibodies stay in your body once they have formed. During your next pregnancy, the antibodies can cross the placenta (the organ that grows in the uterus to provide oxygen and nutrients to the fetus) and attack the red blood cells of the fetus. Rh incompatibility can cause Rh disease, a serious condition that can cause a severe type of anemia.
Your health care provider will order blood tests during your first trimester of pregnancy. This is often done at your first prenatal visit. These tests can check if you have Rh factor and if your body has made antibodies.
- During your pregnancy, injections of a medicine called Rh immune globulin can keep your body from making Rh antibodies. It helps prevent the problems of Rh incompatibility.
- After delivery, if your baby is born Rh-positive, you'll need another injection of the Rh immune globulin. But if you're Rh-negative and your baby is born Rh-negative, you don't need any other treatment.
- If treatment is needed for the baby, it may include phototherapy (light therapy) if treatment is needed for jaundice, supplements to help the body make red blood cells, or in severe cases a blood transfusion.
Early prenatal care and treatment help prevent issues with Rh incompatibility.
It sits within Blood, Heart and Circulation and Pregnancy and Reproduction.
When to speak to someone. Reading about a topic cannot tell you whether it applies to you. Speak to a doctor or pharmacist if symptoms are severe, sudden, getting worse, or simply not going away — and seek emergency care immediately for chest pain, breathing difficulty, sudden weakness or confusion, or a serious allergic reaction.
Research on Rh Incompatibility
4 studies areregistered for this condition on ClinicalTrials.gov, the U.S. National Library of Medicine's public registry. A selection is below — the links go straight to the registry entry, not to a summary of ours.
What a registered study does and does not mean. Registration means a study exists and has been declared publicly. It says nothing about whether the treatment being tested works, is safe, or is available to you. Many studies find no benefit — that is what research is for. Never seek out an experimental treatment on the strength of a registry entry alone.
Research currently under way
- The Efficacy of Ursodeoxycholic Acid (UDCA) as Adjuvant Therapy to Phototherapy in the Management of Neonatal Indirect HyperbilirubinemiaTishreen University Hospital
Research already completed
- Stannsoporfin With Light Therapy for Newborn Babies With JaundiceInfaCare Pharmaceuticals Corporation, a Mallinckrodt Company
- Development a Rhesus Type Compatibility Test by Means of an Antibody Able to Recognize RH1 Antigen Grafted on a BiochipCentre Hospitalier Universitaire de Besancon
Study data from ClinicalTrials.gov, a service of the U.S. National Library of Medicine. Retrieved 2026-07-30. Registry entries are supplied by study sponsors and investigators; ClinicalTrials.gov does not verify their scientific validity. PocketsInfo is not affiliated with, and not endorsed by, the NLM or the NIH.
Where to read more
Rather than paraphrase, we point you to the primary sources. Every link below is to a government health agency, a national institute or a recognised medical body — grouped by what you are trying to find out.
Learn More
- Fetal-maternal erythrocyte distribution blood testMedical Encyclopedia
- Hemolytic disease of the newbornMedical Encyclopedia
- Hydrops fetalisMedical Encyclopedia
- Hydrops Fetalis/Erythroblastosis FetalisChildren's Hospital and Health System, Inc.
- Red Blood Cell Antibody ScreenNational Library of Medicine
- Rh Factor Blood TestMayo Foundation for Medical Education and Research
- Rh Factor: How It Can Affect Your PregnancyAmerican College of Obstetricians and Gynecologists
- Rh incompatibilityMedical Encyclopedia
- Rh Incompatibility during PregnancyNemours Foundation
Clinical Trials
- ClinicalTrials.gov: Erythroblastosis, FetalNational Institutes of Health
Medical subject headings
Clinicians and researchers index this subject under Rh Isoimmunization, Erythroblastosis, Fetal. These are the terms to use when searching medical literature.
This page is built from the MedlinePlus health topic record for Rh Incompatibility, a service of the U.S. National Library of Medicine (NLM), National Institutes of Health. Information is from MedlinePlus.gov. PocketsInfo is not affiliated with, and is not endorsed by, the NLM or the NIH. Retrieved 30 July 2026.