CLS 306 BB lecture 11

What is hemolytic disease of the fetus and newborn (HDFN)?

incompatibility between maternal antibodies and fetal RBC antigens

• maternal antibodies destroy fetal RBCs

What is the medical condition caused by maternal antibody destruction of fetal RBCs called?

Erythroblastosis Fetalis (EF)

When can HDFN occur?

In utero (prepartum) and after birth (postpartum)

What antibody class causes HDFN?

IgG

• crossed placenta

What condition can develop in the fetus due to severe EF?

Hydrops Fetalis (HF)

• anemia

• edema

• cardiac failure

• death

What are the three classifications of Hemolytic Disease of the Fetus & Newborn (HDFN)?

ABO: most common. mother incompatibility w/ baby

Rh: anti-D most common or caused by other Rh abs

Other (non-Rh immune antibodies): rare. jk, K, Fy, S

What is a common reason mothers develop anti-K antibodies?

Previous multiple blood transfusions

Why is anti-K especially important in HDFN?

second most common cause of severe HDFN

what are the major dangers of HDFN during pregnancy (in-utero/prepartum)?

• Severe fetal anemia

• Fetal heart failure

• Fetal death

What happens to the fetus in HDFN during pregnancy?

Maternal IgG antibodies attack fetal RBCs, causing fetal anemia and potentially Hydrops Fetalis (HF)

What is released when fetal RBCs are destroyed in HDFN?

Unconjugated (indirect) bilirubin

Why is unconjugated bilirubin less harmful in utero?

It is cleared through the mother’s liver via the placenta, preventing bilirubin buildup in the fetus

What blood bank tests are performed at the first obstetrical visit?

ABO, Rh (including Du), and Antibody Screen (ABS)

What is done if the initial antibody screen is negative?

Repeat ABS at ~24 weeks

What is done if the antibody screen is positive?

• Perform Antibody Identification (Ab ID)

• If antibody is IgG, perform an antibody titer

What should be done with maternal samples when antibodies are detected?

Retain all maternal samples

How are maternal antibody titers monitored?

• Perform periodic titers

• > 1:32 is considered clinically significant

• Run previous and current samples in parallel

What does an increase in maternal antibody titer indicate?

Increased risk and severity of HDFN

What additional testing may be done if maternal antibody titer is high?

Amniocentesis to test fetal cells (amniocytes) for antigen presence

Why may the father be tested in regards to prenatal care?

To verify whether he is antigen positive, helping assess fetal risk

When is amniocentesis performed in suspected HDFN?

When maternal antibody titers are elevated and HDFN is suspected

What is amniocentesis and when is it done?

Removal of amniotic fluid from the womb, typically at 18–20 weeks gestation

What does amniotic fluid bilirubin indicate?

Severity of HDFN

How is bilirubin measured in amniotic fluid?

Using a spectrophotometer scanning increasing wavelengths to detect absorbance at 450 nm

What does an increase in ΔOD₄₅₀ indicate?

Rising bilirubin levels → worsening severity of HDFN

What does the Queenan curve for ΔOD₄₅₀ show in HDFN monitoring?

amniotic fluid bilirubin levels (ΔOD₄₅₀ at 450 nm) with gestational age to assess severity of HDFN

Higher ΔOD₄₅₀ = more hemolysis = more severe HDFN

What is an intrauterine transfusion (IUT)?

direct transfusion of blood to the fetus to treat severe HDFN–related anemia

When is intrauterine transfusion indicated?

When one or more of the following are present:

• Fetal hydrops on ultrasound

• Fetal Hgb < 10 g/dL (severe anemia)

• High ΔOD₄₅₀ on Liley graph or Queenan curve (severe hyperbilirubinemia)

What are the blood product requirements for an intrauterine transfusion (IUT)?

• RBCs

  • < 5 days old

  • CPDA-1 or AS-3 preservative (no mannitol)

  • Antigen-negative to corresponding maternal alloantibody

• O neg

• CMV-negative or *leukoreduced (“CMV-safe”)

• Hemoglobin S–negative

• Irradiated

• AB FFP (if plasma is required)

Why are CPDA-1 or AS-3 used for IUT RBCs?

They lack mannitol, a diuretic that is unsafe for fetuses/neonates

What are the dangers of HDFN after birth (postpartum)?

• Continued maternal antibody RBC destruction

  • Severe anemia → may cause cardiac failure

  • Hepatomegaly

  • Splenomegaly

  • Jaundice due to immature neonatal liver → accumulation of unconjugated (indirect) bilirubin; Hyperbilirubinemia (toxic)

  • Kernicterus if untreated unconjugated bilirubin → severe neurologic damage/retardation, potentially death

How is neonatal hyperbilirubinemia treated in HDFN?

• Phototherapy (460–490 nm): Converts unconjugated (indirect) bilirubin into less lipophilic, less toxic isomers that can be excreted

  • unconjugated/indirect bilirubin sensitive to strong light

• Exchange transfusion: Indicated when Hgb < 10 g/dL or bilirubin ≥ 20 mg/dL to rapidly remove bilirubin and maternal antibodies

  • if phototherapy doesnt work

What is a neonatal exchange transfusion?

postpartum treatment that replaces the neonate’s blood to remove unconjugated bilirubin and maternal antibodies and stop ongoing hemolysis

When is exchange transfusion chosen over phototherapy?

• When phototherapy fails to control rising bilirubin

• When maternal antibodies are rapidly destroying fetal RBCs

What are the clinical triggers for neonatal exchange transfusion?

• Hemoglobin < 10 g/dL

• Total bilirubin ≥ 20 mg/dL

How is exchange transfusion performed in neonates?

Via umbilical cord access or peripheral extremities, depending on age

What RBC characteristics are required for neonatal exchange transfusion?

• < 5 days old

• CPDA-1 or AS-3 (no mannitol)

• Antigen-negative to maternal alloantibody

• O neg

• CMV-negative or leukoreduced

• Hgb S neg

• Irradiated

What plasma is used in neonatal exchange transfusion? Why can Rh type be disregarded for plasma?

• Universal plasma donor

• Contains no anti-A or anti-B antibodies

• Prevents plasma incompatibility

Plasma contains no RBCs, therefore no Rh antigens

Why is the neonatal exchange transfusion performed slowly?

to avoid:

• Clinically significant hemodynamic shifts

• Metabolic abnormalities

What vascular access routes are used for neonatal exchange transfusion?

• UVC = Umbilical Venous Catheter

• UAC = Umbilical Arterial Catheter

What are the beneficial effects of a 2-volume exchange transfusion?

• Removes ~50% of bilirubin

• Removes 80–90% of sensitized infant RBCs

• Removes 80–90% of maternal incompatible antibodies

• Replaces incompatible RBCs with compatible RBCs

What is ABO HDFN?

most common form of HDFN, caused by maternal ABO antibodies reacting with fetal RBCs

When can ABO HDFN occur?

First pregnancy and subsequent pregnancies — no prior exposure required

what is the most common ABO combination causing HDFN?

Type O mother (IgG anti-A,B) with a Type A neonate

• (Type B neonate is less common)

How severe is ABO HDFN compared to Rh HDFN?

Usually milder than Rh HDFN

What symptoms are typically seen in ABO HDFN?

Mild to moderate jaundice

Is maternal prenatal testing predictive of ABO HDFN?

No — prenatal testing is usually not predictive

What is the purpose of the cord blood work-up?

To evaluate the newborn for HDFN and identify maternal antibodies attached to fetal RBCs

What tests are performed on the mother postpartum?

• Repeat ABO/Rh

• Antibody Screen (ABS)
  (Usually done at hospital admission prior to delivery)

What tests are performed on the baby in a cord blood work-up?

• ABO/Rh typing (including weak D)

• Direct Antiglobulin Test (DAT)

What does a positive IgG DAT in the newborn indicate?

Maternal IgG antibodies are coating the baby’s RBCs

What is an elution and why is it performed?

• procedure uses baby rbcs + supernatant media

• Removes antibody from baby’s RBCs using heat or chemicals

• The antibody is recovered in the supernatant for antibody identification

• Antibody identified is of maternal origin

How is ABO HDFN confirmed using an eluate?

Test the eluate against A₁ and B reagent cells

Why do some hospitals avoid elution testing in newborns?

• Requires large blood volume

• Risk of iatrogenic anemia (anemia caused by excessive blood draws)

Can ABO HDFN be prevented?

No (unlike Rh HDFN)

What is the most common treatment for ABO HDFN?

Phototherapy for hyperbilirubinemia/jaundice

When is an exchange transfusion indicated in ABO HDFN?

When bilirubin ≥ 20 mg/dL

Which antibodies cause Rh0(D) HDFN?

• Anti-D (most common)

• Other Rh antibodies: anti-C, anti-c, anti-E, anti-e

How severe is Rh0(D) HDFN compared to other types?

most severe form of HDFN

What are the major clinical consequences of Rh0(D) HDFN?

• Severe fetal/neonatal anemia

• Severe hyperbilirubinemia/jaundice

• Risk of kernicterus

Which pregnancies are usually affected by Rh0(D) HDFN?

2nd or subsequent pregnancies after maternal alloimmunization at 1st pregnancy

What events can cause maternal sensitization leading to Rh0(D) HDFN?

• Prior delivery

• Miscarriages or abortions

• Prenatal fetal–maternal hemorrhage

Which antibodies can cause Rh HDFN, and how severe are they?

• Anti-D: most common; mild → severe

• Anti-E: usually mild

• Anti-c: mild → severe

• Anti-e: rare

• Anti-C: rare

• Antibody combinations (e.g., anti-c + anti-E): can be severe

What prenatal tests are performed on the mother for Rh HDFN?

• ABO & Rh typing (including Du)

• Antibody Screen (ABS)

What is done if the maternal antibody screen is positive?

• Antibody ID

• Antibody titer

• Optional: father’s antigen status

• IgG subclass determination if indicated

How are Rh antibody titers monitored during pregnancy?

• Establish initial titer

• Repeat every ~4 weeks

• Run previous and current samples in parallel

When is further fetal testing indicated in Rh HDFN?

When antibody titer is > 1:32

What fetal tests are used when Rh antibody titers are high?

• MCA-PSV Doppler ultrasound (noninvasive; predicts fetal anemia)

• Amniocentesis (less commonly used)

What postpartum tests are performed on the mother?

• Repeat ABO/Rh and ABS

• If ABS positive → Antibody ID

  • weak anti-D:

    • May be due to antepartum Rh Immune Globulin (RhIG)

    • Must verify OB history

    • if due to RhIG: Report as “passive anti-D”, not alloanti-D

What tests are performed on the baby postpartum?

• ABO/Rh typing (including weak D)

• Direct Antiglobulin Test (DAT)

What is the purpose of elution testing in Rh HDFN?

• Removes antibody from neonatal RBCs

• Identifies maternal antibody using antibody ID panel cells

What postpartum laboratory testing is performed for Rh0(D) HDFN?

Qualitative test: Fetal Hgb Screen / Rosette Test

• detect D-positive fetal cells in a D-negative mother

Quantitative test: Kleihauer–Betke (KB) Test

• Measures the amount of fetal blood in maternal circulation

• Maternal blood is acid-treated and stained

• Fetal RBCs resist acid and stain; maternal RBCs become “ghost” cells

• Count fetal cells among 2,000 maternal cells

• Fetal blood volume = (# fetal cells × maternal blood volume) ÷ 2,000

What is Rh Immune Globulin (RhIG)?

A pharmaceutical drug of anti-D antibodies

• given to Rh neg moms known to be neg for allo anti-D + exposed to Rh+ rbcs

How is RhIG administered?

Intramuscular injection

• pre-measured 1 mL syringe with attached needle

When is the micro-dose RhIG given and what does it cover?

• Indications: abortion, miscarriage, ectopic pregnancy

• Administration: ≤ 12 weeks gestation (antepartum)

• Dose: 50 μg anti-D

• Protects against 2.5 mL Rh+ RBCs or 5 mL Rh+ whole blood

When is the full-dose RhIG given and what does it cover?

• Indications: amniocentesis, cordocentesis, abdominal trauma, antepartum hemorrhage, postpartum

• Administration:

  • After abortion/miscarriage >12 weeks

  • ≥ 28 weeks gestation (antepartum)

  • Within 72 hours postpartum if infant is Rh+ or Rh unknown

• Dose: 300 μg anti-D

• Protects against: 15 mL Rh+ RBCs or 30 mL Rh+ whole blood

How is the number of RhIG vials calculated postpartum?

Fetal cell volume (from KB test) ÷ 30 = number of syringes

• < 0.5 → round down (e.g., 2.2 → 2)

• ≥ 0.5 → round up (e.g., 2.7 → 3)

• The calculation is an estimate — adding +1 vial ensures adequate protection