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Rh ISOIMMUNIZATION

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  1. antibodies produced against a specific RBC antigen as a result of antigenic stimulation with RBC of another individual
  2. most common is anti-Rh Ab produced by a sensitized Rh-negative mother
  3. other antibodies can lead to fetal red blood cell hemolysis --->much less common and no prophylaxis is available

Pathogenesis

  1. maternal-fetal circulation normally separated by placental barrier
  2. upon first exposure, initially IgM and then IgG antibodies are produced;IgG antibodies cross the placental barrier
  3. sensitization routes

    • incompatible blood transfusion
    • previous fetal-maternal transplacental hemorrhage
    • invasive procedure while pregnant
    • therapeutic abortion, D&C, amniocentesis

  4. 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

  1. routine screening at first visit for blood group, Rh status, antibodies
  2. Ab titres < 1:16 considered benign
  3. 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
  4. Liley curve is used to determine bilirubin level and appropriate
    management
  5. 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

  1. Rhogam binds to Rh Ag of fetus and prevents it from contacting maternal immune system
  2. 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

  3. if Rh neg and Ab screen positive, follow mother with serial monthly  Ab titres throughout pregnancy +/- serial amniocentesis as needed (Rhogam of no benefit)
Treatment

  1. falling biliary pigment warrants no intervention (usually indicative of fetus which is unaffected or mildly affected)
  2. 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)
  3. 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

Rh ISOIMMUNIZATION Rh ISOIMMUNIZATION Reviewed by Radiology Madeeasy on September 09, 2010 Rating: 5
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