ALLOIMMUNIZATION IN PREGNANCY

1. ALLOIMMUNIZATION IN PREGNANCY Brooke Grizzell, M.D. PGY-2 OBGYN Department, UKSM September 28th, 2005

2. Objectives • 1. Understand history of HDFN • 2. Learn correct terminology • 3. Outline ABO and CDE blood groups “Major blood group antigens” • 4. Discuss Minor blood group antigens, including Kell, Lewis, Duffy, and various others • 5. Review clinical management • 6. Compare Delta OD 450 and MCA-PSV • 7. Provide Rh alloimmunization management summary • 8. Learn prevention strategies

3. History of HDFN 1609: First case of HDFN described 1939: Levine & Stetson described antibody 1941: Levine demonstrated causal relationship between anti-D antibodies and HDFN 1945: Neonatal exchange transfusion began 1956: Bevis proposed amniotic fluid assessment 1961: Liley proposed amniotic fluid assessment 1963: Liley introduced intraperitoneal fetal transfusion 1968: Rh immune globulin (RhoGAM) introduced 1980’s: Real-time ultrasound 1990’s: Genetic techniques to perform fetal RBC typing

4. “erythroblastosis fetalis” vs. “hemolytic disease of the fetus and newborn” (HDFN) “alloimmunization” vs. isoimmuniation” Correct Terminology

5. Pathophysiology • After 1st antigenic exposure, memory B lymphocytes recognize appearance of RBC’s containing the antigen in subsequent pregnancies • B lymphocytes - plasma cells - IgG • Initial IgM response changes to IgG

6. Pathophysiology- Continued • Maternal antibodies cross placenta- attach to fetal RBC’s- lead to RBC destruction • Sequestration by macrophages in fetal spleen-extravascular hemolysis-produces fetal anemia

7. ABO Blood Group • Invariably causes only mild disease • Treatment generally limited to phototherapy • No need for antenatal detection

8. CDE (Rhesus) System • Very important!!! • Includes c, C, D, e, E • D negativity defined as absence of D antigen • Only 87% of Caucasians carry the D antigen

9. Various Other Antibodies • Antigens such as A, P, Le (a), M, I, IH, and Sd (a) are innocuous • Most are IgM • Lewis antibodies and cold agglutinins of I are prevalent but not clinically significant

10. Antibodies Associated with HDFN • Anti-c, Anti-D, Anti-E, and Anti-Kell • RhoGAM has decreased HDFN caused by anti-D, but Anti-D antibody is still MOST COMMON CAUSE of red cell alloimmunization

11. Minor RBC Antigens • Kell is most common of minor • Responsible for 10% of cases of severe antibody-mediated anemia • Mechanism of anemia two-fold 1. Hemolysis 2. Suppression of erythropoiesis **Transfuse women with Kell(-) blood**

12. Minor RBC Antigens (continued) • Lewis antigen also a common minor RBC antigen • Most anti-Lewis antibodies are IgM antibodies • Mothers with anti-Le (a) antibodies who require transfusion, need blood negative for the Le(a) antigen

13. Minor RBC Antigens (continued) • Duffy antigens Fy(a) and Fy(b) • Only anti-Fy(a) antibody associated with HDFN- may range from mild to severe • ACOG: treat sensitization to minor RBC antigens similar to those with Rh alloimmunization

14. Minor Antigens (continued) • MNS system = M, N, S, s, U antigens • Anti-M and anti-N naturally occurring- no clinical significance • Anti-S, anti-s, and anti-U antibodies ~ mild to severe HDFN

15. Clinical Management • 1. Routine blood type &AB screen • 2. Repeat AB screen at 24-28 wga for Rh (-) women prior to receiving RhoGAM (some recommend repeat screens for Rh (+) women also) • 3. If AB screen is (+), identify antibody and potential for HDFN

16. Clinical Management (cont) • 4. Elicit risk factors for alloimmunization(past pregnancies, transfusions, shared needles) • 5. Determine father’s RBC antigen status and zygosity • 6. If paternity unknown or father is (+) for antigen, fetus is at RISK

17. Clinical Management (cont) • 6. (cont) Obtain antibody titer~ the reciprocal of the highest dilution still giving a positive reaction ACOG: Consider invasive testing at titer of 1:32 or greater by indirect Coombs (1:16 most often used) **Titers less reliable after a sensitized pregnancy**

18. Clinical Management (cont) • 7. If AB titer remains below critical titer- invasive testing can be deferred and pt. evaluated by serial AB titers • Serial titers before 18-20 wga not necessary • If critical titer noted at first visit, amnio for delta OD450 at 22-24 wga

19. Clinical Management (cont) • 8. Obtain amniocytes to determine fetal blood type if father is heterozygous for the antigen responsible for alloimmunization • 9. MCA-PSV can be used as early as 18 wga ~ if greater than 1.5 MoM, consider fetal blood sampling

20. Clinical Management (cont) • 10. Serial amnio to measure delta OD450 and plot values on Liley or Queenan graph • Delta OD450 vs. MCA-PSV

21. Delta OD450 • Spectral analysis of amniotic fluid at 450 nm proposed in 1961 by Liley- measures change in OD • Measures the level of bilirubin and predicts severity of hemolytic disease after 27 wga • Delivery or intrauterine transfusion if delta OD450 falls into zone III or upper zone II

23. Queenan Method • Proposed another method of using delta OD450 • Suggested four zones in his graph

25. Limitations of spectral analysis • Kell-antigen sensitized pregnancies • Erythroid suppression and hemolysis • Not an accurate prediction of fetal anemia

26. MCA-PSV • Velocity of blood flow in brain increased with anemia b/c of 1. Increased cardiac output 2. Vasodilation in the brain 3. Decreased blood viscosity • Prospective studies 111 fetuses~ 100% sensitivity 125 fetuses~ 88% sens. and 98% NPV

27. Correct Technique for MCA Doppler • Fetus resting • Circle of Willis imaged in axial image using color doppler • Entire length of MCA • Close to origin of internal carotid artery

28. Limitations of Each Method • Delta OD450 falsely elevated in presence of mec or blood • Delta OD450 misleadingly low after inadvertent exposure to light or in Kell alloimmunization • MCA accuracy diminishes after 35 wga and after multiple transfusions

29. Comparison Studies? • Few have been completed • Small retrospective studies 28 pregnancies~ 100% sens. using Doppler MCA-PSV vs. 80% sens. using amnio and delta OD450 Another study with 28 pregnancies~ 75% sens and 60% PPV using MCA-PSV vs. 75% and 53% respectively for delta OD450

30. Cordocentesis • Gold standard for detection of fetal anemia • Complications! • 2.7% total risk of fetal loss • Reserved for patients with increased MCA-PSV or delta OD450

31. Advantages of MCA-PSV • Non-invasive • Mother not put at risk for worsening alloimmunization • Can be used with alloantibodies other than RhD, including anti-Kell antibodies

32. Summary of Management for Rh Alloimmunization • Monthly indirect coombs titer (in first sensitized pregnancy) • If critical titer reached, determine paternal and fetal antigen status • Amniocentesis and delta OD450 OR MCA-PSV ** For 2nd or greater sensitized pregnancy, initiate amnio or MCA at 18-20 wga**

33. Rh Alloimmunization management (cont) • If using MCA-PSV, and initial is less than 1.5 MoM, do weekly testing x 3 wks • Regression line/slope • Repeat testing Q 1-4 wks • Cordocentesis or delivery once MCA-PSV reaches 1.5 MoM

34. Prevention of Alloimmunization • ACOG recommends RhoGAM for Rh (-) pts after 1st trimester loss • RhoGAM for threatened abortion controversial- no evidence based recomm. • 50 mcg dose protects against 2.5 ml of Rh (+) RBC’s • 300 mcg dose protects against 15 ml of RBC’s or 30 ml of Rh (+) blood

35. Prevention (cont) • Give 300 mcg dose within 72 hrs of delivery to unsensitized Rh (-) women (Rh positive infant) • ACOG: 300 mcg at 28 wga UNLESS father known to be Rh (-) • Repeat Antibody Screen ?

36. Prevention (cont) • Test for excessive fetal-maternal hemorrhage after blunt trauma, abruption, cordocentesis, and bleeding assoc. with previa • Kleihauer Betke or rosette test • Give RhoGAM for partial molar pregnancy, SAB, TAB, ectopic, chorionic villus sampling, external version

37. Conclusions • Remember the instances in which to consider RhoGAM -SAB, TAB, threatened AB (controversial), ectopic, previa/bleeding, abruption, partial molar, CVS, blunt trauma, cordocentesis • Clinically important antibodies: Anti-c, Anti-D, Anti-E, and Anti-Kell, Rarely Anti-Duffy Fy(a) • Usually not associated with severe HDFN:Anti-Lewis, ABO incompatibilities, Anti-Duffy(Fy-b) antibodies, (Duffy Fy-a causes mild to severe HDFN), Anti-A, Anti-P, Anti-M, Anti-I, Anti-IH, Anti-Sd(a)

38. Conclusions (cont) • Anti-D still most common cause of red cell alloimmunization, despite RhoGAM • Kell = most common minor antigen *anemia mechanism 2-fold • Critical titer most often used is 1:16 by indirect coombs • Amnio with delta OD450 vs. MCA-PSV • Liley or Queenan graphs • Remember AB screens and indications for RhoGAM!!

39. References 1. Gabbe Obstetrics – Normal and Problem Pregnancies, 4th edition. 2. Creasy R., Resnik R., Iams J., Maternal Fetal Medicine Principles and Practice, 5th edition. 3. ACOG Compendium 2005 4. Harkness U., Spinnato J., Prevention and Management of RhD isoimmunization. Clinics in Perinatology, Dec 2004 31:4. 5. Pereira L., Jenkins T., Conventional management of maternal red cell alloimmunization compared with management by Doppler assessment of MCA-PSV. American Journal of Obstetrics and Gynecology, Oct 2003 189:4.

40. References (cont) 6. Cohen D., Hemolytic disease of the newborn: RBC alloantibodies in pregnancy and associated serologic issues. Up to Date, Oct 2004. 7. Barss V., Moise K., Significance of minor red blood cell antibodies during pregnancy. Up to Date, Apr 2005.