Hemolytic Disease of the Newborn

Question 1

In general terms, what is hemolytic disease of the newborn caused by?

Answer 1

blood group incompatibility between mother and fetus

Question 2

What is hydrops fetalis? Is it specific to HDN?

Answer 2

It’s a fatal, severe accumulation of fluid in the fetus - not specific for HDN

Question 3

What blood group is usually the issue in HDN?

Answer 3

It’s when the fetus inherits RhD antigen from dad when mom is Rh negative

Question 4

Which pregnancy is usually affected and why>

Answer 4

The first is NOT affected because mom isn’t exposed to baby’s blood until later in the pregnancy and it takes longer for IgG to start being produced (IgM can’t cross the placenta). So it’s the NEXT pregnancy that’s the concern

Question 5

What are some of the symptoms in HDN?

Answer 5

Anemia, which leads to extramedullary hematopoiesis and cardiac decompensation (leading to hydrops)
hemoglobin degradation leads to jaundice and kernicterus

Question 6

If the HDN is mild, extramedullary hematotpoiesis where in the body may produce enough red cells to maintain normal numbers?

Answer 6

spleen and liver

Question 7

The jaundice that occurs in HDN, is it from conjugated or unconjugated billirubin?

Answer 7

unconjugated (indirect bilirubinemia)

Question 8

What is kernicterus?

Answer 8

it’s when unconjugated bilirubin binds to llipids in the brain causing serious damage to the CNS - the brain is edematous and yellow

Question 9

What does the amount of antiD antibodies formed by mom depend on?

Answer 9

Depends on how much baby blood she was exposed to - she’ll only start making antibodies after she’s received more than 0.5 to 1 mL of Rh+ cells

Question 10

How do you diagnose HDN?

Answer 10

1. direct antiblobulin test will be positive in the baby because baby’s cells are coated with mom’s antibodies
2. indirect antibolubilin test will be positive in mom

Question 11

How do you prevent Rh-mediated HDN?

Answer 11

You give a drug called rhogam to the mom at 28 weeks and within 72 hours of delivery

Question 12

What is Rhogam?

Answer 12

It’s anti-D antibodies (which sounds counterintuitive) that can’t cross the placenta. This means they can “mop” up any Rh+ baby cells that get into mom’s circulation before mom’s immune system gets a chance to form antibodies against them

Question 13

How do you determine what dose of Rhogam to give the second time?

Answer 13

You have to determine the amount of fetomaternal hemorrhage

Question 14

What tests can you use to determine the amount of fetomaternal hemorrhage?

Answer 14

1. Kleihauer-Betke test - you prepare a smear of mom’s blood, expose to acid bath (which removes adult Hb, but not fetal Hb). Then stain the smear and look at it - mom’s cells will look pale and baby’s will still be dark - then just count them and get a percentage
2. Flow cytometry test - use mom’s blood, apply anti–HbF antibody with fluorescent tag, run though gel and look for intense staining in the HbF region - that has to be from baby’s blood

Question 15

Does HDN occur with the ABO blood antigens?

Answer 15

Yes - incompatibility in 25% of pregnancies, but only 10% of those have HDN and only 1 in 200 need treatment

Question 16

Why is ABO incompatibility rarely serious?

Answer 16

because most Anti-A and anti-B antibodies are IgM and can’t cross, plus baby cells express A and B poorly still

Question 17

ABO hemolytic disease occurs almost exclusively in infants born to what blood type of mom?

Answer 17

babys usually A or B, born to an O mom

Question 18

What’s the protection for ABO incompatibility

Answer 18

there isn’t one

Question 19

WHat’s the treatment for HDN?

Answer 19

1. minimally affected - phototherapy
2. severely affected - total exchange transfusion through umbilical vein
3. plasmapheresis of the mom to remove antibody
4. high dose IV immunoglobulin can be used too