Haemolytic Disease of the Fetus/Newborn

Question 1

What is the cause of HDFN?

Answer 1

HDFN is caused by sensitized maternal antibodies that cross the placenta and cause destruction to fetal RBCs.

Question 2

Which antibodies are responsible for causing HDFN and why?

Answer 2

IgG antibodies cause HDFN, because they can cross the placenta.

Question 3

Why does anti-D cause the most severe form of HDFN?

Answer 3

Anti-D is very immunogenic and is an IgG antibody.

Question 4

How is this controlled?

Answer 4

Anti-D prophylactic treatment.

Question 5

What are other antigens that cause severe HDFN?

Answer 5

Antigens of the Kell, Duffy, and Kidd system.

Question 6

How can a Rh-negative mother also be sensitized to produce anti-D, without being pregnant with a Rh-positive child?

Answer 6

By receiving a blood transfusion from Rh-positive donor blood.

Question 7

Why is ABO HDFN hardly ever severe?

Answer 7

1. Fetal RBCs express less of ABO antigens at birth.
2. ABO antigens are distributed throughout the body and on fetal tissues, which reduce the pressure and target on fetal RBCs.

Question 8

What HDFN does the ABO system cause?

Answer 8

ABO HDFN causes prolonged neonatal jaundice and anaemia.

Question 9

What are other blood groups that less commonly cause HDFN?

Answer 9

Antigens of the Kell (anti-K and rarely anti-k), Duffy (anti-Fya), Kidd (anti-JKa and anti-JKb), and MNS adn s antigens.

Question 10

How does HDFN occur?

Answer 10

1. Exposure
2. Immune attack
   3 RBC destruction

Question 11

What happens when RBCs are destroyed in the haemolytic process?

Answer 11

The fetal haematopoietic system is stimulated to increase RBC production, which will ultimately lead to extramedullary haematopoiesis (in liver and spleen). If this fail, anaemia will arise.

Question 12

What are secondary causes of severe anaemia?

Answer 12

Severe anaemia:

• Cardiac failure
• Generalized edema (erythroblastosis faetalis)

Question 13

What happens in less severe cases?

Answer 13

RBC destruction continues after birth, which will result in deposition of increased unconjugated bilirubin. Immature liver cannot produce enough glucuronidase to metabolize the unconjugated bilirubin, therefore the bilirubin will deposit into lipid rich tissue in the skin and brain, causing kernicterus and ultimately brain damage.

Question 14

What are the antenatal serological testing procedures for determining HDFN?

Answer 14

• ABO grouping
• RH grouping
• Allo-Ab screening (IAT)
• Allo-Ab identification (if IAT is +)
• Ab Titer strength determination
• Cordocentesis (Fetal blood sampling)
• Parental RBC phenotyping

Question 15

How would you go about in testing HDFN postnatally?

Answer 15

Serological Investigation:

• IAT on mother’s serum
• DAT on baby’s RBCs
• ABO grouping on mother and baby
• Elution testing on baby’s RBCs set up against A, B, and O cells

Question 16

What must be done on all pregnant women booked in and at 28 weeks of gestation?

Answer 16

-ABO, RH, Ab screening

Question 17

What must be done if pregnant women have anti-D, anti-c, and antibodies to Kell system?

Answer 17

-Check Ab Titer strength and for additional RBC antibodies monthly to 28 weeks and every 2 weeks before delivery

Question 18

What must be done in pregnant women who have any other RBC antibodies?

Answer 18

-Ab titer strength when booked in and again at 28 weeks

Question 19

What must be done in pregnant women with previous history of HDFN or if anti-D or Kell related antibodies show increase in titer?

Answer 19

• Refer to specialist for further assessment and antenatal intervention:
  1. Intrauterine transfusion
  2. Amniocentesis

Question 20

What is done during postnatal severity assessments?

Answer 20

(a) Collect infant cord blood and perform:
- ABO, RH, Ab screening, Hb, Bi.
(b) Collect maternal blood and perform:
- ABO, RH, Ab Sc., determine degree of FMH

Question 21

What is done during antenatal severity assessments?

Answer 21

1. Monitor the amount of anti-D in mother’s serum during pregnancy
2. Ab titrations during pregnancy
3. Assessment of fetal anaemia:
   - Amniocentesis and Cordocentesis
   - Cerebral artery Doppler studies
4. Exchange and Intrauterine transfusions given to fetus in severe cases

Question 22

What is done during postnatal severity assessments?

Answer 22

(a) Collect infant cord blood and perform:
- ABO, RH, Ab screening, DAT (+ do elution), Hb, Bi.
(b) Collect maternal blood and perform:
- ABO, RH, Ab Sc., determine degree of FMH

Question 23

How is HDFN prevented?

Answer 23

• Intramuscular injection of anti-D must be administered 72 hrs after FMH occurred.
• Dosage of anti-D depend on the degree of FMH.
• Dosage is 125 iu for every 1mL of fetal blood that have entered the mother’s circulation.
• Prophylactic treatment with Anti-D prevent the mother’s antibodies from being senstitized by the fetal RBCs and elicit an immune response against them in 2nd or subsequent pregnancies.