Fetal and Neonatal alloimmune Thrombocytopenia

Question 1

What is fetal and neonatal alloimmune thrombocytopenia?

Answer 1

Platelet destruction due to maternal antibody against platelet antigen (HPA-1a used to be called ZWa)

Question 2

What are the fetal risks of NAIT?

Answer 2

• Need for PUBS
• 11% had emergent c-section at time of PUBS
• Intracranial hemorrhage or hemorrhage into other viscera
• Petechiae
• Ecchymosis

Question 3

What patients are candidates for a work-up of possible NAIT?

Answer 3

• Previously affected child
• US findings consistent with intracranial hemorrhage (52% are seen on US)
• Siblings of affected mother (?)

Question 4

When working up a patient for NAIT, what work-up do you perform?

Answer 4

• Maternal and Paternal platelet HPA typing and zygosity (typing can be done by genotyping or by serology)
• Assess maternal titer (antiHPA 1a antibody level) which correlates to disease severity but not always
• Use Amniocytes or NIPT to assess fetal platelet typing (genotyping is used)

Question 5

What are the most common platelet antigens involved with NAIT?

Answer 5

There are 15. HPA-1a is most common. There is also HPA-1b

Question 6

What percentage of NAIT is caused by HPA-1a antigen?

Answer 6

?

Majority are caused by this antigen.

Question 7

You perform HPA1a/HPA1b platelet antigen testing on both parents. Results are as follow:
Maternal: negative for HPA1a/1b antigens
Paternal: positive for HPA1a antigen. Negative for HPA1b

How do you interpret these results?

Answer 7

Paternal homozygous - then fetus is heterozygous and at risk for NAIT

Paterna heterozygous - then fetus could be negative or heterozygous

Question 8

You perform HPA1a/HPA1b platelet antigen testing on both parents. Results are as follow:
Maternal: negative for HPA1a/1b antigens
Paternal: positive for HPA1a antigen. Negative for HPA1b

Based on these results what is the next step in your evaluation?

Answer 8

• If father is heterozygous then NIPT or amnio to assess for fetal platelet genotyping
• Assess maternal titer (anti HPA1a levels)

Question 9

You order maternal platelet antibody testing. The patient returns positive for HPA-1a antibody. You perform genotype testing and determine the mother is homozygous HPA 1B/1B and the father is homozygous HPA 1A/1A. Based on these results what are the risks to the fetus?

Answer 9

Significant risk of platelet destruction.

Question 10

You order maternal platelet antibody testing. The patient returns positive for HPA-1a antibody. You perform genotype testing and determine the mother is homozygous HPA 1B/1B and the father is homozygous HPA 1A/1A.

Will you offer this patient treatment? If so, what?

Answer 10

If patient has history of affected child; start IV I G weekly and add prednisone by mouth later

(History of intracranial hemorrhage in previous pregnancy that was discovered before 28 weeks)

Question 11

How do you follow a pregnancy with a patient at risk of NAIT?

Answer 11

• Fetal Growth
• Antenatal testing and assessment for fetal hemorrhage
• Percutaneous umbilical blood sampling at 32 weeks to assess response to IV I G and prednisone if vaginal delivery is desired
• No vaginal delivery if platelet is found to be below 50,000

Question 12

What are the treatment options for patients with NAIT?

Answer 12

IVI G plus or minus oral prednisone

Serial maternal platelet transfusion

Question 13

How do you manage the delivery in a patient with NAIT?

Answer 13

Cesarean section at term

Question 14

What percentage of fetal intracranial hemorrhage is associated with NAIT occur in the first pregnancy?

Answer 14

50-60%

Question 15

What percentage of NAIT pregnancies will be complicated by fetal intracranial hemorrhage?

Answer 15

15%

Question 16

When do the majority of intracranial hemorrhage related to NAIT occur?

Answer 16

Before 28 weeks

Question 17

What are ultrasound findings of FNAIT?

Answer 17

Ultrasonographic findings may include intraventricular, periventricular, or parenchymal hemorrhage