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Isoimmunization Ch 16

Isoimmunization Ch 16. 2009-2010 Academic Year MSIII Ob/Gyn Clerkship Self-Directed Study. Case Study.

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Isoimmunization Ch 16

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  1. IsoimmunizationCh 16 2009-2010 Academic Year MSIII Ob/Gyn Clerkship Self-Directed Study USUHS MSIII Ob/Gyn Clerkship Self Directed Studies

  2. Case Study 24 yo G2P0010 at 12 weeks ega presents for routine antenatal visit. Blood type is A negative. She had a spontaneous abortion with her first pregnancy 2 years ago. She cannot remember if she ever received Rhogam. On her initial OB labs, her antibody titer returns at 1:128. Discuss this case, including management of Rh- women with respect to antibody titer and fetal risks. USUHS MSIII Ob/Gyn Clerkship Self Directed Studies

  3. APGO Educational Topic 19: • A. Describe the pathophysiology of isoimmunization, including: • Red blood cell antigens. • Clinical circumstances under which D isoimmunization is likely to occur. • B. Discuss the use of immunoglobulin prophylaxis during pregnancy for the prevention of isoimmunization. • C. Discuss the methods used to identify maternal isoimmunization and the severity of fetal involvement. USUHS MSIII Ob/Gyn Clerkship Self Directed Studies

  4. Pathophysiology • Rh-negative = Absence of Rh antigen on RBC’s. • Many proteins make up Rh complex, but the D protein (or antigen) is most commonly associated with isoimmunization (90% cases) • Sensitization = Rh neg person exponsed to the Rh (D) antigen and makes antibodies against that protein (antigen). USUHS MSIII Ob/Gyn Clerkship Self Directed Studies

  5. How does Mom become Sensitized? • Undetected placental leak of fetal RBC’s (Rh+) into maternal (Rh-) circulation. • Grandmother theory – Mom (Rh-) is sensitized at birth by receiving Rh+ cells from her mother during delivery. • Usually need 2 exposures to produce sensitization unless 1st is massive. • 1st causes Mom to realize it is “foreign” • 2nd causes a memory response  rapid antibody production  attacks fetal RBC’s. “Hemolytic disease of Fetus/Newborn”. USUHS MSIII Ob/Gyn Clerkship Self Directed Studies

  6. Pathophysiology (cont’d) • Exposure occurs during pregnancy or at delivery • Initial antibody production is IgM (does NOT cross placenta) • Subsequent antibody production (with 2nd exposure) is IgG (does CROSS placenta) If hx of hydrops, risk in next pregnancy is approx 90% IgG  crosses placenta  attacks Rh+ antigen on baby’s RBCs  hemolysis. Mild hemolysis  increased erythropoesis, no anemia. Severe hemolysis  anemia  CHF  Hydrops Fetalis  IUFD USUHS MSIII Ob/Gyn Clerkship Self Directed Studies

  7. RhogamRh immune globulin Algorithm for use for Rh- mothers with no Rh antibodies Rhogam 300 ug 28 ega Within 72hr delivery Indirect Coomb’s Test Rhogam 300 ug Negative Kleihauer- Betke Test Negative 10 ug Rhogam per ml of fetal blood Positive Any ega 1st Trimester Rhogam 300 ug Amniocentesis Abortion or Ectopic Rhogam 50 ug Rhogam 300 ug Negative Suspected Feto-maternal Hemorrhage Kleihauer- Betke Test 10 ug Rhogam per ml of fetal blood Positive USUHS MSIII Ob/Gyn Clerkship Self Directed Studies

  8. Identification of Maternal Isoimmunization • Mother is Rh- • Father is Rh+  determine ABO status • Example: Father is B+ If Dad is B+/+ = B+ then all of his children will be Rh+ If Dad is B+/- = B+ then ½ of this father’s children will be Rh+ and ½ will be Rh- USUHS MSIII Ob/Gyn Clerkship Self Directed Studies

  9. If Mom is at risk for Baby with Rh+ • Antibody screen at new OB labs with titer • If titer is < 1:16, fetus NOT at risk • Repeat titer every 2-4 weeks • If titer is > 1:16, fetus may be at risk • Consider invasive testing USUHS MSIII Ob/Gyn Clerkship Self Directed Studies

  10. Testing for Fetal Disease • Amniotic Fluid Spectrophotometry • 27 weeks ega; correlates biliary pigment and fetal hct • DeltaOD 450 measurements compared on Liley chart • Ultrasound • Fetal growth; placental size and thickness; liver size; ascites; pleural effusion; pericardial effusion; skin edema • Middle Cerebral Artery (MCA) peak velocity doppler flow correlates with anemia. • Percutaneous Umbilical Blood Sampling (PUBS) • Test fetal blood for hgb, hct, blood gases, pH, bilirubin USUHS MSIII Ob/Gyn Clerkship Self Directed Studies

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