Chapter 12 Hemolytic Disease of the Fetus & Newborn Flashcards
What is HDFN also known as?
Erythroblastosis fetalis.
What occurs immunologically in a fetomaternal hemorrhage?
Maternal antibodies can form due to fetal cells getting into the maternal circulation.
What can cause a fetomaternal hemorrhage?
- Delivery (when placenta separates).
- Amniocentesis.
- Abortion (spontaneous or induced)
- Cordocentesis
- Ectopic pregnancy
- Abdominal trauma
Note: For most women a small amount of fetal blood enters the maternal circulation during the birthing process. Usually less than 30 mL. More than 30mL occurs 0.4% of the time.
What happens in the baby as red cells are destroyed due to HDFN?
Bilirubin (indirect) levels increase.
Remember:
Indirect Bilirubin = Unconjugated
What are the cause of most maternal IgG’s that result in HDFN?
Previous pregnancies.
Only 4% are due to formation of antibodies from transfusion exposure to foreign RBC antigens.
What does the fetus lack to convert unconjugated to conjugated bilirubin?
Enzyme glucoronyl transferase.
What is the process as heme is broken down?
- Heme is broken down –> converts to unconjugated bilirubin. Not soluble in water and attaches to albumin and goes to the liver.
- Enzyme glucoronyl transferase adds a carbohydrate to it to make it conjugated bilirubin.
- Goes to bile, then to intestines. Broken down by bacteria and is eliminated in the stool. Also is water soluble and can be excreted in urine as well.
How is indirect bilirubin processed for the fetus?
Indirect bilirubin crosses through the placenta and is conjugated by the maternal liver.
In HDFN, what is the result of fetal erythropoiesis?
As RBC destruction continues:
1. Erythroblasts are released (erythroblastosis fetalis), spleen and liver may enlarge.
2. Edema occurs in the peritoneal and pleural cavities (hydrops fetalis).
What can be the result in the fetus if it has uncompensated anemia?
Cardiac failure may result.
What is the difference right after birth on how the baby processes bilirubin?
- No new Abs entering the neonate.
- Newborn cannot conjugate bilirubin as it lacks glucuronyl transferase.
- Unconjugated bilirubin binds to albumin and then to tissues (jaundice).
- Permanent brain damage (kernicterus) may result if bilirubin binds to tissues of the central nervous system - this can be fatal.
Look at the diagrams on Slide 9 (p288 of TB).
What are normal bilirubin levels after the baby is born?
<1 day - 24 to 149 umol/L
1 to 2 days old - 58 to 197 umol/L
3 to 5 days old - 26 to 205 umol/L
Then in normal situations, the infant starts to produce the enzyme and levels of unconjugated bilirubin drop right off.
5 days to 60 years old - 5 to 21 umol/L.
What are the three important factors that must occur for HDFN to occur?
- RBC Ab must by IgG
- Fetus must possess an antigen that the mother lacks. (Gene is inherited from the father).
- Ag must be well developed at birth.
- Lewis, Lutheran, I, IH, P1 NOT well developed.
- Can be Rh (D), ABO or other antibodies.
What antigen group causes the most severe HDFN?
Rh group most severe.
D-neg women are sensitized during the 1st pregnancy with a D-pos baby (w/o intervention).
–> Subsequent pregnancies are affected.
In Rh HDFN if the baby’s blood has the DAT test what is the result?
Positive direct antiglobulin test (DAT).
If the baby has HDFN what are the symptoms?
Jaundice and/or anemia may occur.
What extreme treatment may be required for the baby with HDFN?
Exchange transfusion may be necessary.
What is the preventative treatment for Rh HDFN?
Rh immune globulin (RhIG) given to Rh neg expectant individuals to prevent Rh HDFN.
[Can be called RhoGam in other countries.]
Note: Before RhIG, D antibodies were responsible for 95% of all HDFN cases. Now it is almost no more common than other HDFN fatalities but still the most common.
What is the most common type of HDFN at 1 in 125 births?
ABO HDFN.
What is the blood group situation that causes ABO HDFN?
Mom: Group O
Baby: Group A or B blood.
Group O people have Anti-A,B that is IgG and can cross the placenta even in the first pregnancy. Most common but very mild.
Why are symptoms of ABO HDFN mild? What are the mild symptoms?
Possibly due to:
1. A or B substances in tissue that may neutralize Abs.
2. Fetal/infant RBCs may be poorly developed.
3. Fetal/infant RBC sites may be reduced.
Some jaundice may occur.
What is used to treat mild symptoms of ABO HDFN?
Phototherapy can be used to treat jaundice.
What other blood group types/antibodies can cause severe HDFN?
Other Rh, Kell, Kidd, Duffy (Fya), S, and U antigens have caused severe HDFN.
Any IgG can cause HDFN.
What blood groups/antibodies have caused mild cases of HDFN?
ABO, i, Fyb and Lutheran antibodies have caused mild HDFN.
What blood groups/antibodies have never been associated with HDFN?
Lewis, I, P1 antibodies have never been associated with HDFN.
What can you test to get a clue that HDFN could occur with a low-freq antigen?
Agglutination with paternal cells and maternal serum is a clue to a low-frequency antigen.
What does initial prenatal testing include? Why?
Type and screen on pregnant individuals.
Because:
1. Identifies D-neg women who are candidates for RhIG.
2. Identifies women with antibodies capable of causing HDFN.
Any pregnant person that has a known Ab is followed very closely during their pregnancy.
Review slide 18 for follow up prenatal testing.
When is RhIG given in the pregnancy if needed?
Given at week 28.
What is the purpose of doing an antibody titration?
Titration helps determine whether certain procedures should be performed.
E.g. Amniocentesis, ultrasound, cordocentesis, etc.
If an antibody has been detected what is the process for titration?
Baseline titer is determined in the first trimester and repeated at 4 to 6 week intervals (sample is frozen for future testing).
a) A titer that rises by 2 dilutions (compared to baseline) is significant.
b) A titer of 16 or 32 is usually critical for anti-D and other Rh antibodies.
Note: If the titre is at a high level or increasing at an alarming level testing will be done to monitor the fetus.
See slide 21 for titration figure.
What noninvasive diagnostic test can be done to detect fetal anemia? How is the severity determined?
Color Doppler ultrasonography can detect fetal anemia.
–> Increased cardiac output and low blood viscosity, and therefore increased flow velocity.
Severity of anemia is determined by evaluating the peak systolic velocity in the middle cerebral artery.
What is the purpose of doing an amniocentesis for potential cases of HDFN?
Determine level of bilirubin pigment in amniotic fluid.
How is the bilirubin pigment in amniotic fluid measured?
- Scanned spectrophotometrically from 350 to 700 nm
- A change in optical density (ΔOD) above baseline (450 nm) is a measure of bilirubin
- The ΔOD is plotted on a Liley graph (using gestational age)
What are the zones related to disease severity on the Liley graph?
Upper zone (zone 3): severe HDFN
Middle zone (zone 2): moderate disease
Lower zone (zone 1): mild disease
See slide 24 for illustration.
What are the options based on results after the amniocentesis?
- Pregnancy continues to term
- Intrauterine transfusion is performed
- Early labor is induced. Fetal lung maturity must be determined (lecithin:sphingomyelin [L:S] ratio should be greater than 2:1)
What is the purpose of doing a cordocentesis?
Fetal blood sample is taken for:
1. Hemoglobin and hematocrit
2. Bilirubin testing
3. RBC genotyping
4. Cordocentesis can be used for intravascular transfusions in cases of severe HDFN
Note: Mortality rate is low (1% to 2%)
In the 2nd trimester what info can be gained about the fetus using maternal plasma? What is the advantage of that?
Fetal DNA can by typed.
Predicting the fetal genotype could avoid amniocentesis or cordocentesis if the fetus lacks the antigen.
What postpartum testing is or may be done?
Maternal:
1. ABO/D typing
2. Ab screen
3. Ab ID
4. Fetal screen (rosette)
5. Kleihauer-Betke
Cord or Infant:
1. ABO/D typing
2. DAT
3. Elution
See slide 28 for details of the purpose of each and situations when required.
What infants are D testing performed on?
All infants born to D negative mothers are tested, including for weak D antigen.
What can result in false-negative results when testing the infant for D antigen?
False-negative results:
D antigen sites are blocked by antibody (blocking phenomenon)
Perform elution (will demonstrate anti-D antibody)
What can result in false-positive results when testing the infant for D antigen?
False-positive results:
Weak D test is performed on RBCs coated with antibodies
Rh control will be positive at antihuman globulin (AHG) phase
What ABO testing is performed on infants?
ABO testing
Only the forward grouping is performed
ABO antibodies are not yet produced
How is the cord blood processed?
Cord blood is washed to remove Wharton’s jelly
What may be required if the DAT is positive?
Elution may be necessary if the test is positive and if the mother’s antibody has not been identified or the maternal serum sample is unavailable
What are the possible outcomes of eluate testing if the DAT is positive?
- If the eluate is negative, an antibody to low-frequency antigen is suspected
- If the eluate is positive with A or B cells and negative with screening cells, ABO HDFN is indicated
What cautions should be taken in interpreting type tests and DAT if the infant had intrauterine transfusions?
ABO/D and DAT results should be interpreted with caution in newborns who have had intrauterine transfusions:
- Cord blood may phenotype as group O, D-negative blood because group O, D-negative unit is given
- DAT may be falsely negative or weakly positive
What does giving RhIG do for the mother and baby?
- RhIG prevents alloimmunization in D negative mothers. Concentrated IgG anti-D
- Exact mechanism not well understood, but suppresses immune response after exposure to D fetal RBCs so mother does not produce anti-D
- RhIG only prevents formation of anti-D
How is the typical protocol for antepartum or postpartum administration of RhIG?
Antepartum administration:
- Initial dose (300 μg) is given at 28 weeks gestation
Postpartum administration:
- Non-immunized women receive one full dose of RhIG within 72 hours of delivery
More than one dose may be necessary if the mother has fetomaternal hemorrhage of more than 30 mL
Note: 300 μg is enough to cover a fetomaternal bleed of 30 mL whole blood. Must still do testing to make sure this will be enough.
What are RhIG candidates screened for? Common method?
RhIG candidates are screened for fetomaternal hemorrhage
Most common screening method is the rosette test
How is the rosette screening test done? How is it interpreted?
Rosette test:
1. Uses postpartum maternal specimen
2. Maternal RBCs are incubated with anti-D antibody
3. D-positive indicator cells are added
4. Rosettes are observed under the microscope
a) Less than 1 rosette per 3 low-power fields: one dose of RhIG
b) More than 1 rosette per 3 low-power fields: bleed must be quantitated
See slide 34 for procedure.
How is the amount of fetomaternal bleed quantified?
To quantify the amount of the bleed a test called the Kleihauer-Betke test, must be performed or flow cytometry.
What is the treatment based purpose the Kleihauer-Betke test is performed for?
To calculate the additional doses of RhIG, flow cytometry or the Kleihauer-Betke test is performed.
What is the basis of the Kleihauer-Betke test?
Kleihauer-Betke test is based on the fact that:
- Fetal hemoglobin is resistant to acid (retains dye)
- Adult hemoglobin is not resistant to acid (ghost-like)
How is the Kleihauer-Betke test performed?
- Make blood smear
- Expose to acid buffer
- Wash
- Stain
- Examine under microscope
How is the additional doses of RhIG calculated?
- Estimate volume of fetal blood in maternal circulation. % of fetal cells counted x maternal blood volume.
- Calculate how many vials are needed: each 300ug dose of RhIG protects against a 30 mL whole blood bleed.
- Round up or down to whole number.
Add 1 vial of RhIG to calculated dose to provide safety margin.
See slide 36 for more details on the calculation method.
What is the purpose of performing an intrauterine transfusion?
Corrects anemia and prevents heart failure
What are the requirements for blood given in an intrauterine transfusion?
Blood for intrauterine transfusion:
1. Group O, D-negative RBCs
2. RBCs collected within 7 days (fresh)
3. Irradiated to prevent Graft versus Host Disease
4. Negative for cytomegalovirus
5. Hemoglobin S-negative
What is the initial treatment for hyperbilirubinemia in neonates? What if treatment is not successful?
Phototherapy - Initial treatment for hyperbilirubinemia
1. Mild cases of HDFN, such as ABO HDFN
2. Uses fluorescent blue light (420 to 475 nm)
3. Light converts bilirubin to isomers that are excreted in the bile
If patient is unresponsive, exchange transfusion may be necessary
What is an exchange transfusion and what does it accomplish?
Exchange transfusion after birth
1. Replacement of 1 to 2 whole blood volumes
2. Corrects anemia without expanding the blood volume
3. Removes newborn’s RBCs and replaces them with antigen negative cells
4. Reduces high levels of unconjugated bilirubin (prevents kernicterus)
5. Reduces maternal antibody
What pretransfusion testing is done before an exchange transfusion in an infant?
- ABO and D typing is determined in the infant
- Maternal or infant serum or plasma is used for antibody screening
- Antigen-negative units are given if antibody is present
See table 12.5.
