Hemolytic Disease of the Fetus and Newborn (HDFN)

HDFN

AKA Erythroblastosis Fetalis

• Fetal or newborn RBCS destroyed by maternal IgG

• Maternal Antibodies:

  • Cross placenta

  • Sensitize fetal RBCs

  • Shorten RBC survival

HDFN etiology: when and how does fetomaternal hemorrhage occur?

• may occur when fetal cells escape into the maternal circulation

  • Delivery

  • Amniocentesis

  • Abortion

  • Cordocentesis

  • Ectopic pregnancy

  • Abdominal trauma

HDFN Etiology: How does Antibody Production and RBC Destruction occur?

Fetal RBC antigens (mother lacks) stimulate maternal antibody production → antibodies bind to fetal antigens → RBC destruction

HDFN causes BEFORE birth

• Indirect bilirubin conjugated by the maternal liver

• As RBC destruction continues, fetal

  erythropoiesis increases

  • Erythroblasts release →

    erythroblastosis fetalis

  • Edema occurs (hydrops fetalis)

• Cardiac failure may result

HDFN etiology: after birth

• Newborn cannot conjugate bilirubin

• jaundice and possible kernicterus

Three important factors of HDFN

1. RBC antibody must be IgG

   • Only IgG crosses the placenta

2. Fetus possess an antigen that mother lacks

   • Gene inherited from the father

3. Antigen present at birth

Main Types of HDFN

• Rh (D antigen)

• ABO

• Other Antibodies

Rh HDFN

• Most severe

• D-negative womensensitized during the first pregnancy with a D-positive baby

• Subsequent pregnancies are affected

• Positive DAT

• Jaundice and/or anemia may occur

• Exchange transfusion may be necessary

• Treatment: Rh immune globulin (RhIG)

ABO HDFN

• Most common type of HDFN (1 in 150 births)

  • Mom = group O; baby = group A or B

  • First pregnancy may be affected

• Mild symptoms possibly due to

  • A or B substances in tissue = neutralize antibodies

  • Fetal/infant RBCs = poorly developed

  • Fetal/infant RBC sites = reduced

• Some jaundice may occur

  • Phototherapy treatment

Other Types of HDFN

• Any IgG can cause HDFN

• Common causes: Anti-c and anti-K antibodies

• Less Common: Kell Abs, Kidd Abs, Duffy, S, and U antigens

• Agglutination with paternal cells and maternal serum = a low-frequency antigen

Prenatal Testing Purposes

1. Identifies D-negative women that have RhIG

2. Identifies women with antibodies capable of causing HDFN

Prenatal Testing Identify Women at Risk of HDFN

Antibody Titration

• Determines if procedures are needed

• Baseline titer in 1st trimester, repeated every 4-6 weeks (sample frozen)

  • Significant rise: 2+ dilutions from baseline

  • Critical levels: 16 or 32 for anti-D and other Rh Abs

Ultrasound

• detects fetal anemia

  • Increased cardiac output and low blood viscosity

• Severity of anemia determined by peak systolic velocity in the middle cerebral artery

Amniocentesis

ΔOD is plotted on a Liley graph (using gestational age)

• Upper zone (zone 3): severe HDFN

• Middle zone (zone 2): moderate disease

• Lower zone (zone 1): mild disease

Amniocentesis Result Alternatives

1. Pregnancy continues to term

2. Intrauterine transfusion is performed

3. Early labor is induced

   • Fetal lung maturity must be determined ([L:S] ratio should be > 2:1)

Cordocentesis

• Fetal blood sample is taken for:

  • Hemoglobin and hematocrit testing

  • Bilirubin testing

  • RBC genotyping

• Mortality rate low (1-2%)

• can be used for intravascular transfusions when severe HDFN

Fetal Genotyping

• Fetal DNA typed via maternal plasma in 2nd trimester.

• Predicts fetal genotype to avoid invasive procedures if antigen is absent.

Postpartum Testing

• D testing for infants of D-negative mothers (including weak D).

• Possible false results:

  • False negative: blocked D-antigen sites (perform elution to show anti-D Ab).

  • False positive: weak D test on antibody-coated RBCs (Rh control positive at AHG phase).

Testing at Delivery (Postpartum Testing)

ABO testing (Postpartum Testing)

• Only forward grouping performed

• ABO antibodies not yet produced

• Cord blood is washed to remove Wharton’s jelly (umbilical cord protection)

DAT (Postpartum Testing)

Elution is necessary if DAT is positive and mother’s antibody is unknown or sample unavailable.

• Negative eluate: suspect low-frequency antigen.

• Positive eluate (A/B cells, negative screen): indicates ABO HDFN.

Intrauterine Transfusions

Interpret ABO/Rh and DAT results carefully

• cord blood may show group O, D-negative phenotype due to transfused blood

• DAT results may be falsely negative or weakly positive.

Prevention of HDFN

• RhIG prevents alloimmunization in D-negative mothers

• Prevents formation of anti-D antibody

• Antepartum administration: 300 μg at 28 weeks

• Postpartum administration

Postpartum administration includes ? for HDFN prevention

• Non-immunized women receive one full dose within 72 hours of delivery

• More than one dose if fetomaternal hemorrhage >30 mL

Screening for Fetomaternal Hemorrhage

• Screen RhIG candidates for fetomaternal hemorrhage.

• Perform rosette test on postpartum maternal specimen.

• Incubate maternal RBCs with anti-D antibody.

• Add D-positive indicator cells.

• Rosette observation

Rosette Test and Observation

• ≤1 rosette/3 low-power fields: 1 RhIG dose.

• >1 rosette/3 low-power fields: Quantify bleed needed.

Quantifying Fetomaternal Hemorrhage

• Flow cytometry or Kleihauer-Betke test quantifies fetomaternal hemorrhage for additional RhIG doses.

• Kleihauer-Betke test:

  • Fetal hemoglobin resists acid (retains dye)

  • adult hemoglobin does not (ghost-like).

Kleihauer-Betke Calculation

Intrauterine Transfusion

• Corrects anemia and prevents heart failure

• Blood for intrauterine transfusion

  • Group O, D-negative RBCs

  • RBCs collected within 7 days (fresh)

  • Irradiated to prevent graft-versus-host disease

  • Negative for cytomegalovirus and/or leukocyte reduced

  • Negative for hemoglobin S

Phototherapy

• Initial treatment for hyperbilirubinemia

  • Mild cases of HDFN (ex: ABO HDFN )

• Uses fluorescent blue light (420 to 475 nm)

  • Light converts bilirubin to isomers excreted in the bile

• If patient is unresponsive → exchange transfusion

Exchange Transfusion

• Replacement of 1 to 2 whole blood volumes

• Exchange Transfusion

  • Corrects anemia

  • Removes newborn’s RBCs and replaces with antigen-negative cells

  • Reduces bilirubin (preventing kernicterus)

  • Reduces maternal antibodies

Blood Selection for Exchange Transfusion

• ABO and D typing for the infant

• Antibody screening with maternal or infant serum/plasma

• Use antigen-negative units if antibody present