Hemolytic Disease of the Fetus & Newborn

HDFN definition

Hemolytic disease of the fetus and newborn caused by maternal IgG antibodies destroying fetal red blood cells

Cause of HDFN

Maternal antibodies against fetal RBC antigens inherited from the father

Most common antibodies in HDFN

ABO Rh Kell Duffy Kidd and MNS systems

Antibody class in HDFN

IgG antibodies that can cross the placenta

When prenatal testing begins

Around 12 weeks gestation with type and screen

Purpose of type and screen

Determine ABO Rh type and detect maternal antibodies

If antibody screen is positive

Perform antibody identification

Purpose of antibody identification

Determine specificity and clinical significance

Antibody titration frequency

Every 2 to 4 weeks

Purpose of antibody titration

Monitor increase in antibody levels

Critical titer for anti D

16

Significance of rising titer

Indicates increased risk of fetal anemia

Fetal antigen testing

Determines if fetus has antigen targeted by maternal antibody

How fetal antigen status is determined

Paternal testing or cell free fetal DNA

Start of HDFN pathogenesis

Fetal RBCs enter maternal circulation

When sensitization occurs

During pregnancy delivery or procedures

Sensitization

Maternal immune system produces antibodies against fetal antigen

Type of antibodies formed

IgG

Subsequent pregnancy effect

IgG crosses placenta and attacks fetal RBCs

Where hemolysis occurs

Fetal spleen

Result of hemolysis

Fetal anemia

Fetal response to anemia

Increased RBC production

Erythroblastosis

Release of immature nucleated RBCs into circulation

Extramedullary hematopoiesis

RBC production in liver and spleen

Result of extramedullary hematopoiesis

Hepatosplenomegaly

Effect on liver

Decreased albumin production

Consequence of low albumin

Decreased oncotic pressure

Hydrops fetalis

Severe edema ascites and fluid accumulation

Final severe complication

High output cardiac failure

Post birth bilirubin issue

Placenta no longer clears bilirubin

Resulting condition

Hyperbilirubinemia and jaundice

Cause of kernicterus

Unconjugated bilirubin entering brain tissue

Location of brain damage

Basal ganglia and brainstem

Outcome of kernicterus

Neurologic damage or death

Rh immune globulin purpose

Prevents formation of anti D antibodies

Who receives RhIg

Rh negative mothers

When RhIg is given

28 weeks delivery and after fetal maternal hemorrhage

Protection of one RhIg vial

Covers about 30 mL fetal whole blood

Passive anti D

Temporary antibodies from RhIg

Active anti D

Maternal immune response with memory

Rosette test

Qualitative screen for fetal Rh positive cells

Kleihauer Betke test

Quantitative test measuring percent fetal cells

Use of Kleihauer Betke

Calculate RhIg dose

Amniocentesis purpose

Measure bilirubin in amniotic fluid

What bilirubin indicates

Degree of hemolysis

Liley system

Classifies severity of HDFN into zones

Modern alternative to amniocentesis

Doppler ultrasound of middle cerebral artery

PUBS

Percutaneous umbilical blood sampling

What PUBS measures

Fetal hemoglobin hematocrit blood type and DAT

Use of PUBS

Confirm anemia and guide transfusion

Phototherapy purpose

Convert bilirubin to water soluble form

Intrauterine transfusion purpose

Treat fetal anemia before birth

Exchange transfusion purpose

Remove bilirubin antibodies and sensitized RBCs

Blood for intrauterine transfusion

O Rh negative CMV safe leukoreduced irradiated HbS negative fresh

Hematocrit for intrauterine transfusion

75 to 85 percent

Blood for exchange transfusion

O Rh negative RBCs with AB plasma

Goal hematocrit after exchange

40 to 50 percent

Severe antibodies in HDFN

Rh and Kell

Moderate antibodies in HDFN

Duffy and Kidd

Mild antibodies in HDFN

ABO