USUHS MSIII Ob/Gyn Clerkship Self Directed Studies Isoimmunization Ch Academic Year MSIII Ob/Gyn Clerkship Self-Directed Study

USUHS MSIII Ob/Gyn Clerkship Self Directed Studies 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 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 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 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 1 st is massive. –1 st causes Mom to realize it is “foreign” –2 nd causes a memory response  rapid antibody production  attacks fetal RBC’s. “Hemolytic disease of Fetus/Newborn”.

USUHS MSIII Ob/Gyn Clerkship Self Directed Studies Pathophysiology (cont’d) Exposure occurs during pregnancy or at delivery Initial antibody production is IgM (does NOT cross placenta) Subsequent antibody production (with 2 nd 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 Rhogam Rh immune globulin Algorithm for use for Rh- mothers with no Rh antibodies Indirect Coomb’s Test Negative Rhogam 300 ug Amniocentesis 28 ega Any ega Rhogam 300 ug Suspected Feto-maternal Hemorrhage Kleihauer- Betke Test Negative Positive 10 ug Rhogam per ml of fetal blood Rhogam 300 ug Within 72hr delivery Rhogam 300 ug Kleihauer- Betke Test Negative Positive 10 ug Rhogam per ml of fetal blood Abortion or Ectopic Rhogam 50 ug 1 st Trimester

USUHS MSIII Ob/Gyn Clerkship Self Directed Studies Identification of Maternal Isoimmunization Mother is Rh- Father is Rh+  determine ABO status Example: Father is B+ Rh+ Dad Rh- Mom ++ = Pos +- = Pos -- = Neg --/++ = -/+ or -/+ ALL positive --/+- = -/+ or -/- ½ pos & ½ Neg -- = Neg --/++ = -/+ or -/+ ALL positive --/+- = -/+ or -/- ½ pos & ½ Neg 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 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 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