antibodies produced against a specific RBC antigen as a result of antigenic stimulation with RBC of another individual most common is an...
- antibodies produced against a specific RBC antigen as a result of antigenic stimulation with RBC of another individual
- most common is anti-Rh Ab produced by a sensitized Rh-negative mother
- other antibodies can lead to fetal red blood cell hemolysis --->much less common and no prophylaxis is available
Pathogenesis
- maternal-fetal circulation normally separated by placental barrier
- upon first exposure, initially IgM and then IgG antibodies are produced;IgG antibodies cross the placental barrier
- sensitization routes
- incompatible blood transfusion
- previous fetal-maternal transplacental hemorrhage
- invasive procedure while pregnant
- therapeutic abortion, D&C, amniocentesis
- complications
- anti-Rh Ab can cross the placenta and cause fetal hemolysis resulting in fetal anemia, CHF, edema, and ascites
- severe cases can lead to fetal hydrops (total body edema), or erythroblastosis fetalis
Diagnosis
- routine screening at first visit for blood group, Rh status, antibodies
- Ab titres < 1:16 considered benign
- Ab titres > 1:16 necessitates amniocentesis (correlation exists between amount of biliary pigment in amniotic fluid and severity of fetal anemia) from 24 weeks onwards
- Liley curve is used to determine bilirubin level and appropriate
management - Kleihauer-Betke test can be used to determine extent of feto-maternal
hemorrhage - fetal red blood cells are identified on a slide treated with citrate phosphate buffer
- adult hemoglobin is more readily eluted through cell membrane in presence of acid
Prophylaxis
- Rhogam binds to Rh Ag of fetus and prevents it from contacting maternal immune system
- Rhogam must be given to all Rh negative women
- at 28 weeks
- within 48 hours of the birth of an Rh positive fetus
- positive Kleihauer-Betke test
- with any invasive procedure in pregnancy
- in the case of ectopic pregnancy
- with miscarriage, therapeutic abortion
- antepartum hemorrhage
- if Rh neg and Ab screen positive, follow mother with serial monthly Ab titres throughout pregnancy +/- serial amniocentesis as needed (Rhogam of no benefit)
- falling biliary pigment warrants no intervention (usually indicative of fetus which is unaffected or mildly affected)
- rising or stable biliary pigment on serial amniocentesis must be compared to a standard table which is divided into 3 zones based on severity of hemolysis (Liley Curve)
- intrauterine transfusion of O-negative packed red blood cells may be required for severely affected fetus or early delivery of the fetus for exchange transfusion
