Alloimmune Thrombocytopenia
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Transcript Alloimmune Thrombocytopenia
Michael F. McNamara, DO
Sanford Maternal Fetal Medicine
No disclosures
Platelet Disorders in Pregnancy
Gestational thrombocytopenia
Idiopathic thrombocytopenia (ITP)
Thrombotic thrombocytopenia (TTP)
Alloimmune thrombocytopenia (NAIT)
Gestational Thrombocytopenia
Dilution effect
Increase of platelet destruction
No therapy needed
Idiopathic Thrombocytopenia
1-3 / 1000 pregnancies
Pregnancy not usually altering disease
course
Therapy
Steroids
IVIG
Splenectomy
Thrombotic Thrombocytopenia
Purpura (TTP)
TTP/HUS, may be confused with pre
eclampsia
Microangiopathic hemolytic anemia
Thrombocytopenia
Neurologic changes (headache, lethargy)
Thrombotic occlusions in multiple small
vessels
Therapy plasma exchange, platelet
transfusions
Alloimmune Thrombocytopenia
Also known as Neonatal Alloimmune
Thrombocytopenia (NAIT)
0.2 -1 per 1000 deliveries
Low fetal platelets due to maternal
antibodies
Index case usually affected
Antenatal diagnosis often by ultrasound
with findings of intracranial hemorrhage
Case Study
25 year old female
Gravida 5, para 2
Two previous term vaginal deliveries
Petechiae, bruising, platelets < 10,000
Counseled on further pregnancies, need
of treatment
Case Study
Presented at 14 weeks gestation
Genetic counseling, history reviewed
Same paternity as previous infants
Father of baby not available for testing
(zygosity)
Case Study
Diagnostic testing (platelet antigen)
Maternal
Blood HPA 1b/1b
Fetal
Amniotic fluid HPA 1a/1b
Case Study
Preventative therapy
IVIG 1 gram / kg weekly
Prednisone 1mg /kg daily
Case Study
Antenatal Course
Gestational diabetes
Severe headaches with IVIG therapy
Elevated liver enzymes due to percocet
use secondary to headaches
Case Study
Antenatal steroids at 33 weeks gestation
Elected cesarean for delivery with tubal
ligation
Vaginal delivery if umbilical cord
sampling performed with normal fetal
platelet count
Delivery at 37 weeks, uncomplicated
Female infant 5 lbs, 4 oz
Alloimmune thrombocytopenia
Also know as Neonatal Alloimmune
throbocytopenia (NAIT)
Incidence 0.2 -1 per 1000 Caucasian
births
Maternal antigens against fetal platelets
NAIT
Platelet antigens classified at HPA 1a
(PLA1) and HPA 1b (PLA2)
97% adults phenotype HPA 1a (positive
for 1a)
69% adults homozygous HPA 1a (1a/1a)
28 % adults heterozygous HPA 1a
(1a/1b)
3 % adults homozygous HPA 1b (1b/1b)
NAIT
Affected pregnancies
Most serious complication
Intracranial hemorrhage 10-20 % of
cases
25-50 % cases diagnosed prenatally
Ultrasound findings of intracranial
hematoma, porencephalic cysts
Antepartum Preventive Therapy
Extremely High Risk
Previous baby ICH in second trimester
High risk
Previous baby ICH in third trimester
Moderate risk
Previous baby with thrombocytopenia but no
ICH
NAIT
Recurrence risk up to 100%
Thrombocytopenia is severe and
happens earlier in subsequent
pregnancies
Previous ICH is risk factor for severe
thrombocytopenia in next pregnancy
Low platelet count goes lower in
subsequent pregnancies without
treatment in utero
NAIT – antenatal therapy
IVIG – very uncommon for ICH with IVIG
treatment (11/411 for 2.7%)
Prednisone (additionally) – no better
than IVIG alone
Umbilical cord sampling – procedure /
bleeding risk
Platelet transfusions – unknown efficacy
IVIG Mechanism of Action
Provision of missing immunoglobulins or
neutralizing antibodies, restoration of
immune function, and/or suppression of
inflammatory and immune-mediated
processes
Increase the effect of regulatory T cells,
contributing to the maintenance of
immunologic self-tolerance
Prevention of reticuloendothelial uptake of
autoantibody-coated blood cells (eg,
platelets, red cells) through blockade of
macrophage Fc-receptors
Case Study #2
Preconception Counseling
Gravida 3, Para 3 with recent neonatal
demise from ICH delivered at 38 weeks
Low platelet count
Paternal 1a/1b
Maternal 1b/1b
Case Study #2
Pregnancy #4, amniocentesis
Fetus - male1b/1b, normal pregnancy
Pregnancy #5, amniocentesis
Fetus – male,1a/1b, affected
IVIG, prednisone, cord sampling
Cesarean at 37 weeks gestation
Case Study #2
First two pregnancies vaginal deliveries
with no complications
Oldest is a male, second oldest female
Recent testing of the female (now an
adult), 1b/1b
Case Study #2
Platelet antigens classified at HPA 1a
(PLA1) and HPA 1b (PLA2)
97% adults phenotype HPA 1a (positive
for 1a)
69% adults homozygous HPA 1a (1a/1a)
28 % adults heterozygous HPA 1a
(1a/1b)
3 % adults homozygous HPA 1b (1b/1b)
83% chance of having a baby with 1a/1b
Summary
NAIT cause of neonatal
thrombocytopenia
Index case possibly severe problems
such as ICH
Decrease complications with in utero
therapy, IVIG, prednisone