BB F1

• Antibodies


  When attached to antigen, can cause hemolysis and one problem with that is the hemolytic disease of a newborn

  
• IgG


  • Can cross placenta
  • Except IgG2
• Not all IgG can cross placenta that can cause HDN
• Hemolytic disease of the newborn (HDN)


  Clinical condition caused by destruction of the RBCs of the fetus and neonate by antibodies produced by the mother

  
• Factors that must be present for HDN to occur


  • The mother must LACK THE ANTIGEN and following exposure to the antigen from previous pregnancies or transfusions, produce an antibody of the IgG class (anti-D)
  • The fetus must possess the antigen
  • The antigen present in the fetus must be WELL-DEVELOPED AT BIRTH

  
• Disease mechanism of HDN

  1. Hemolysis happens when Ab + Ag (reaction)

  2. IgG (Except IgG2) are the immunoglobulin class that are only actively transported across the placenta

  3. Transfer of antibodies from mother to fetus: Advantage - Most IgG antibodies are directed against bacterial, fungal, and viral antigens, so the transfer of IgG from the mother to the fetus is beneficial. Disadvantage - HDN

  
• Rh hemolytic disease of newborn


  • Responsible for the MOST SEVERE CASES OF HDN
  • MOST COMMON - ABO HDN

  
• First pregnancy: Rh negative mother, Rh positive firstborn


  1. Unaffected - no anti D yet

  2. During gestation, and particularly at delivery when the placenta separates from the uterus, variable numbers of fetal RBCs enter the maternal circulation (also known as FETOMATERNAL HEMORRHAGE)

  
• Fetomaternal hemorrhage can occur in amniocentesis, spontaneous or induced abortion, chorionic villus sampling, ectopic pregnancy, abdominal trauma
• These fetal cells, carrying D antigen inherited from the father, immunize the mother (no D antigen)


  And stimulate the production of anti-D

  
• Once the mother is immunized to D antigen


  All subsequent offspring inheriting the D antigen will be affected
• Subsequent pregnancies: Rh negative mother, Rh positive baby


  1. Affected (HDN)

  2. Rh negative mother already formed Anti D (produced in the 1st pregnancy)

  3. Anti D - IgG that can cross the placenta

  4. Rh positive fetus has presence of D antigen on his/her fetal red cells

  5. Reaction: Anti D + D antigen = Hemolysis (HDN)

  
• Factors affecting immunization and severity


  • Antigenic exposure
  • Host factors
  • Immunoglobulin class
  • Antibody specificity
  • Influence of ABO group
• Antigenic exposure


  Fetomaternal hemorrhage pregnancy can cause significant increases in maternal antibody titers, leading to increased severity of HDN

  
• Transplacental hemorrhage of fetal RBCs into the maternal circulation occurs in up to 7% of women during gestation as determined by the acid elution method for fetal haemoglobin

  
• Using molecular biology techniques, 50 to 65% of pregnant women have nucleated fetal cells in their peripheral blood
• In the majority of cases, the volume of fetomaternal hemorrhage is small; however, as little as 1 mL of fetal RBCs can immunize the mother
• Host factors


  In Rh-negative individuals who are transfused with 200 mL of Rh-positive RBCs, about 85% form anti-D
• Immunoglobulin class


  • IgG is the only Ig transported across the placenta
  • The active transport of IgG begins in second trimester and continues until birth
  • IgG1 and IgG3 are more efficient in RBC hemolysis
• Antibody specificity


  • Of all the RBC antigens, D is the most antigenic
  • Other antigens in the Rh system, such as C, E, and c, are also potent immunogens (although less than D)
  • Of the non-Rh-system antibodies, anti-Kell is considered the most clinically significant in its ability to cause HDN

  
• Influence of ABO group


  • When the mother is ABO-incompatible with the fetus (major incompatibility), the incidence of detectable fetomaternal hemorrhage is decreased
  • The ABO incompatibility protects somewhat against Rh immunization apparently by the hemolysis in the mother's circulation of ABO-incompatible D-positive fetal RBCs before the D antigen can be recognized by the mother's immune system

  
• Pathogenesis: Effect in utero


  1. Hemolysis occurs when maternal IgG attaches to specific antigens of the fetal RBCs

  2. Hemoglobin liberated from the damaged RBCs is metabolized to INDIRECT BILIRUBIN

  3. INDIRECT BILIRUBIN is transported across the placenta, conjugated by the maternal liver, and harmlessly excreted by the mother

  4. As RBC destruction continues, the fetus becomes EXTREMELY ANEMIC

  5. Compensation: stimulate the fetal bone marrow to produce RBCs at an accelerated rate, even to the point that immature RBCs (erythroblasts) are released into the circulation (ERYTHROBLASTOSIS FETALIS)

  6. When the bone marrow fails to produce enough RBCs to keep up with the rate of RBC destruction, erythropoiesis outside the bone marrow (Extramedullary hematopoiesis) is increased in the hematopoietic tissues of the spleen and liver (HEPATOSPLENOMEGALY)

  7. Resultant of the damaged hepatocytes leads to HYPOPROTEINEMIA caused by decreased hepatic production of plasma proteins, leading to development of high-output CARDIAC FAILURE with generalized edema, effusions, and ascites, a condition known as HYDROPS FETALIS

  
• Erythroblastosis fetalis


  Anemia (increased destruction of red blood cells) and the appearance of immature RBCs (erythroblasts) in the peripheral blood of the fetus

  
• Hydrops fetalis


  Hypoproteinemia + Cardiac failure + severe anemia
• Effect in post partum

  1. The process of RBC destruction goes on even after such an infant is delivered alive- in fact, as long as maternal antibody persists in the newborn infant's circulation

  2. RBC destruction continues with the release of INDIRECT BILIRUBIN

  3. The newborn liver is DEFICIENT WITH GLUCORONYL TRANSFERANSE, an enzyme important for the conjugation of bilirubin

  4. As the Indirect bilirubin is released, it binds to ALBUMIN (transport protein) and circulated harmlessly

  5. However, when the binding capacity of the albumin is exceeded the indirect bilirubin BINDS TO TISSUES which result to JAUNDICE

  6. In particular, it may bind to the tissues of the CNS and cause PERMANENT AND IRREVERSIBLE BRAIN DAMAGE - KERNICTERUS, leading to DEAFNESS, MENTAL RETARDATION AND DEATH

  
• Diagnosis and management of Rh HDN: Serologic testing


  1. Perform a type and antibody screen at the first prenatal visit, preferably during the first trimester

  2. Rh test may include Weak D if no immediate reaction with anti-D occurs

  3. Indirect AHG (DAT positive) - The test conditions must be able to detect clinically significant IgG alloantibodies that are reactive at 37 degree celsius and in the antiglobulin phase

  4. Antibody identification - Cold reactive IgM antibodies can be ignored, and the serum can be treated with sulfhydryl reagents to establish the immunoglobulin class

  
• Diagnosis and management of Rh HDN: Paternal phenotype


  A specimen of the father's blood should be obtained and tested for the presence and zygosity of the corresponding antigen, to help determine further testing of the mother and in counseling her about potential treatment plans and complications of HDN

  
• Diagnosis and management of Rh HDN: Amniocyte testing


  1. If the mother has anti-D and the father is most likely to be heterozygoes for the D antigen, amniocentesis can be done as early as 10-12 weeks' gestation to determine whether the amniocytes carry the gene for the D antigen

  2. Amniocytes can be similarly tested for the genes coding c, e

  
• Phase


  Reduce detection of IgM antibodies, which cannot cross the placenta
• Antibody identification


  1. Cold reactive IgM antibodies: anti-I, anti-IH, anti-Lea, anti-Leb, and anti-P1 can be ignored

  2. Serum can be treated with sulfhydryl reagents (dithiothreitol or 2-mercaptoethanol) and then retested with appropriate controls to establish the immunoglobulin class
• Paternal phenotype


  1. Obtain specimen of the father's blood and test for presence and zygosity of the corresponding antigen

  2. Information is helpful in determining further testing of the mother and in counseling her about potential treatment plans and complications of HDN

  
• Amniocyte testing


  1. If the mother has anti-D and the father is most likely to be heterozygous for the D antigen, amniocentesis can be done as early as 10-12 weeks' gestation to determine whether the amniocytes carry the gene for the D antigen

  2. Amniocytes can be similarly tested for the genes coding c, e, C, E, K, Fya, Fyb, Jka, Jkb, and M

  
• Antibody titers


  1. Used to determine the relative concentration of all antibodies capable of crossing the placenta and causing HDN

  2. Critical titer: 16-32

  3. If initial titer is >16 - 2nd titer should be done 18-20 weeks of gestation

  4. Constant titer of 32 or above represents an indication for amniocentesis or percutaneous umbilical blood sampling between 18 and 24 weeks' gestation

  5. Titer is less than 32 - the titer should be repeated at 4-week intervals, beginning at 18-20 week' gestation, and every 2-4 weeks during the third trimester. The last determination should be made within a week of the expected date of delivery

  6. Titrations studies at time of delivery are not recommended as they provide no clinically useful information

  
• Amniocentesis


  1. Insertion of a needle through the mother's abdominal wall and uterus and extraction of fluid from the amniotic sac

  2. Under ultrasound guidance, amniocentesis is done to assess the status of the fetus

  3. Analyte tested: BILIRUBIN - The concentration of bilirubin pigment in the amniotic fluid correlates with the extent of fetal anemia

  4. Amniotic fluid is subjected to a spectrophotometric scan at steadily increasing wavelengths, so that the change in the optical density (OD) at 450 nm (the absorbance of bilirubin) can be calculated

  5. Change in OD is plotted on a Liley graph according to gestational age

  6. Based on this testing, three alternatives exist: allow the pregnancy to continue to term, perform intrauterine transfusion, or induce early labor

  7. Other use: determination of delta red cell phenotype (D, c, E and e, K1/K2, Jka, Jkb)

  
• Cordocentesis/Percutaneous umbilical cord sampling


  1. Process of obtaining fetal blood using ultrasound guided needle in the umbilical vein near the point of placental insertion

  2. Used for: DAT, Hgb, Hct, Bilirubin, ABO, and Rh typing, Ag phenotype and genotype

  3. In severe cases of HDN, PUBS can also be used for direct intravascular transfusion to the fetus

  
• Color Doppler middle cerebral artery peak systolic velocity


  Indicates the direction of the blood flow - Red for arterial blood, Blue for venous blood
• Intrauterine transfusion


  1. Intervention becomes necessary when: Amniotic fluid change in OD 450 nm results are in high zone II or in zone III, Cordocentesis blood sample has hemoglobin level less than 10 g/dL, Fetal hydrops is noted on ultrasound examination

  2. Performed intraperitoneally by injecting the RBCs into the fetal peritoneal cavity where the RBCs can be absorbed into the circulation

  3. Disadvantage: inability to perform the procedure before 25 weeks and variable absorption of red cells

  4. Alternative: PUBS/cordocentesis - Advantage: ability to obtain HCT before transfusion, ability to perform the procedure as early as 17 weeks

  5. Ultimate goal: maintain fetal hemoglobin above 10 g/dL, procedure repeated every 2-4 weeks until 34-36 weeks' gestation or until the delta lungs are mature, when early delivery can be performed

  
• Early delivery


  Used for many years for moderate-to-severe disease to interrupt the transport of maternal antibody to the fetus and to allow exchange transfusion

  
• Phototherapy


  1. After delivery, phototherapy with ultraviolet light can be used to change unconjugated bilirubin to biliverdin

  2. In infants with mild-to-moderate hemolysis, the use of phototherapy may avoid the need for exchange transfusion to treat hyperbilirubinemia and anemia
• Serologic testing of the newborn infant


  ABO grouping (Forward only) - Antibodies are not developed yet