Key Concepts
Introduction
Rh factor: The D antigen on red blood cells. Rh-positive (D+): antigen present (85% of population). Rh-negative (Dā): antigen absent (15%). Rh sensitization mechanism: 1. Rh-negative mother carries Rh-positive fetus (D antigen from father) 2. Fetal RBCs enter maternal circulation (at delivery, trauma, bleeding, procedures) 3. Maternal immune system recognizes D antigen as foreign ā produces anti-D IgG antibodies 4. In subsequent Rh-positive pregnancies: maternal anti-D IgG crosses placenta ā attacks fetal RBCs ā hemolysis 5. Results: hemolytic disease of the fetus and newborn (HDFN), erythroblastosis fetalis, hydrops fetalis, fetal death Indirect Coombs test (indirect antiglobulin test/IAT): - Screens maternal blood for circulating antibodies to Rh antigens - Performed at initial prenatal visit on all women - Negative: no sensitization ā RhoGAM prophylaxis indicated at key points - Positive: sensitization has occurred ā fetal surveillance (MCA Doppler peak systolic velocity ā elevated = fetal anemia ā intrauterine transfusion or delivery) RhoGAM (Rh immune globulin ā anti-D): - 300 mcg IM (covers 30 mL fetal blood or 15 mL fetal RBCs) - Prevents sensitization by clearing fetal RBCs before maternal immune...