Rh Sensitization During Pregnancy: What Happens

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What Happens

If you are Rh-negative

Unless you are given Rh immune globulin just before or after a high-risk event, such as miscarriage, amniocentesis, abortion, ectopic pregnancy, or childbirth, you have a chance of becoming sensitized to an Rh-positive fetus's blood.

If you have been Rh-sensitized in the past

If you have been Rh-sensitized in the past, you must be closely monitored during any pregnancy with an Rh-positive partner because your fetus is more likely to have Rh-positive blood. In response to an Rh-positive fetus, your immune system may quickly develop IgG antibodies, which can cross the placenta and destroy fetal red blood cells. Each subsequent pregnancy with an Rh-positive fetus may produce more serious problems for the fetus. The resulting fetal disease (called Rh disease, hemolytic disease of the newborn, or erythroblastosis fetalis) can be mild to severe.

• Mild Rh disease involves limited destruction of fetal red blood cells, possibly resulting in mild fetal anemia. The fetus can usually be carried to term and requires no special treatment but may have problems with jaundice after birth. Mild Rh disease is more likely to develop in the first pregnancy after sensitization has occurred.
• Moderate Rh disease involves the destruction of larger numbers of fetal red blood cells. The fetus may develop an enlarged liver and may become moderately anemic. The fetus may need to be delivered before term and may require a blood transfusion before (while in the uterus) or after birth. A newborn with moderate Rh disease is watched closely for jaundice.
• Severe Rh disease (fetal hydrops) involves widespread destruction of fetal red blood cells. The fetus develops severe anemia, liver and spleen enlargement, increased bilirubin levels, and fluid retention (edema). The fetus may need one or more blood transfusions before birth. A fetus with severe Rh disease who survives the pregnancy may need a blood exchange. This procedure replaces most of the infant's blood with donor blood (usually type O, Rh-negative).
• A history of pregnancy with Rh disease is a sign that you will need special treatment when you are pregnant with an Rh-positive fetus.

If you have been Rh-sensitized in the past, an Rh-negative fetus cannot trigger an immune reaction.

Last updated:	November 02, 2007
Author:	Kathe Gallagher, MSW
Reviewed By:	Joy Melnikow, MD, MPH - Family Medicine, Gregory A L Davies, MD, FRCSC, FACOG - Maternal-Fetal Medicine
Editors:	Susan Van Houten, RN, BSN, MBA, Tracy Landauer