Overview
What the Mismatch Can Do
Rh incompatibility is a risk state, not an illness that usually makes the pregnant person feel unwell.
REx-PN
REx-PN
Rh incompatibility is a risk state, not an illness that usually makes the pregnant person feel unwell. The concern arises when an Rh-negative pregnant person carries an Rh-positive fetus and fetal red cells enter the maternal circulation. The maternal immune system recognizes the RhD antigen as foreign and may produce anti-D antibodies. These antibodies are IgG, so they can cross the placenta. In a subsequent exposure, maternal anti-D attaches to Rh-positive fetal red cells and marks them for destruction. The resulting hemolysis can cause fetal anemia; severe disease may progress to hydrops fetalis, in which fluid accumulates in fetal tissues or body cavities. After birth, ongoing red-cell destruction can produce pallor, anemia, jaundice, and bilirubin-related complications. The red-cell transfer is called fetomaternal hemorrhage (FMH). Delivery is a common time for FMH, but bleeding, pregnancy loss, abdominal trauma, or an obstetric procedure can also expose the maternal circulation to fetal cells. A very small exposure can be enough to prime the immune response: an FMH of at least 0.1 mL of Rh-positive fetal red cells is considered potentially sensitizing. The practical...
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