Rh Incompatibility and Isoimmunization
by Cynthia M. Johnson, MA
Rh factor is a protein on red blood cells. Rh incompatibility is when a mother has Rh-negative blood and her baby has Rh-positive blood. Rh isoimmunization is when the blood from the baby makes the mother's body create antibodies that can harm the baby's blood cells.
A baby's Rh status comes from the mother and father. If the mother is Rh negative and the father is Rh positive, the baby has at least a 50% chance of being Rh positive.
Rh isoimmunization can happen if the baby's Rh positive blood enters the mother's blood flow. This may happen during:
The mix in blood happens most often at the end of pregnancy. This means it is rarely a problem in a woman's first pregnancy. The mother's antibodies could affect a future pregnancy with a baby with Rh-positive blood even if the blood is not mixed.
A woman can also become sensitized to Rh-positive blood if she has a blood transfusion that is not a match.
The risk of Rh incompatibility is higher in an Rh-negative pregnant woman who:
Symptoms will only be in the baby. They can be mild to severe, such as:
A woman's Rh factor is tested at routine visits. Blood tests will be done to:
An amniocentesis may also be done. It removes and tests a small amount of the fluid that surrounds the baby to find out if the baby is Rh positive.
The goal of treatment is to keep the baby healthy and lower the risk of this problem in future pregnancies.
Rh incompatibility will be treated by giving the mother Rh immune globulin to prevent Rh isoimmunization.
Not all babies will need to be treated. Those who do may need:
Rh incompatibility can be prevented with an injection of Rh immune globulin at week 28 of the pregnancy. A second injection will be given within 72 hours after delivery. The injections will block the mother's body from developing antibodies.
Women at risk may also be given these injections after a miscarriage, induced abortion, or ectopic pregnancy. These injections will protect the current pregnancy and future pregnancies.
Early and regular prenatal care can also help find and treat these problems before they happen.
American Congress of Obstetricians and Gynecologists
American Pregnancy Association
The Society of Obstetricians and Gynaecologists of Canada
Women's Health Matters
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Updated November 26, 2019. Accessed July 22, 2020.
Last reviewed March 2020 by EBSCO Medical Review Board Elliot M. Levine, MD, FACOG
Last Updated: 3/16/2021
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