Rh Incompatibility and Isoimmunization: Causes
Rh factor is a protein that may be found on the surface of red blood cells. If you carry this protein, your blood is Rh positive. If you don't carry this protein, your blood is Rh negative.
Sometimes a mother with Rh-negative blood is pregnant with a baby that has Rh-positive blood. This can cause a problem if the baby's blood enters the mother's blood flow. The Rh-positive blood from the baby will make the mother's body create antibodies. This is called isoimmunization. The antibodies will attack any Rh-positive blood cells. This will not cause a problem for the mother. However, the antibodies can pass to the developing baby and destroy some of the baby's blood cells.
Fortunately, Rh incompatibility is often prevented with an immunization. If the condition is not prevented, the baby may need care.
A baby's Rh status is determined 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. However, Rh isoimmunization will only happen if the baby's Rh-positive blood enters the mother's blood flow. In most pregnancies, the mother's and baby's blood will not mix. The baby's blood may come into contact with the mother's blood flow during:
- Induced abortion
- Ectopic pregnancy
- Trauma during pregnancy
- Amniocentesis or other invasive testing procedures related to pregnancy—rare
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 receives an incompatible blood transfusion.
Blood Flow to Fetus
Copyright © Nucleus Medical Media, Inc.
Last reviewedMarch 2014by Andrea Chisholm, MD
Please be aware that this information is provided to supplement the care provided by your physician. It is neither intended nor implied to be a substitute for professional medical advice. CALL YOUR HEALTHCARE PROVIDER IMMEDIATELY IF YOU THINK YOU MAY HAVE A MEDICAL EMERGENCY. Always seek the advice of your physician or other qualified health provider prior to starting any new treatment or with any questions you may have regarding a medical condition.