Introduction:

•  It is thrombocytopenia occurring in neonates due to development of antiplatelet antibodies
• Occurs in first pregnancy in 50% of cases

Epidemiology:

• Prevalence- 1-2 in 1000 pregnancies
•  Higher prevalence in women with HLA-B8, HLA-DR3 and HLA-DR52a haplotypes

Etiology:

•  Anti-Human Platelet Antigen-1A antibody (80% cases)
• Anti HPA 5b antibody (15% cases)
• Anti HPA 3a antibody

Pathogenesis:

Passage of HPA positive platelets (which fetus inherits from father) into mother, who is HPA negative

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Production of anti-HPA antibodies

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Antibodies pass through placenta

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Lysis of HPA Positive fetal platelets

Clinical Features:

• Asymptomatic/ mild bleeding complaints
• Severe bleeding 
  • IC bleed is seen in 10-20% untreated cases. These neonates develop long-term neurodevelopmental sequelae
  • Visceral hemorrhage
• Useful clinical pointer- Less than 50,000/cmm platelet count within first 24-48 hrs of life in term infant where there is no evidence of common causes of thrombocytopenia
• No family history of thrombocytopenia
• Recovery of counts occur in 1-2 weeks

Investigations:

•  Test for circulating maternal allo-antibodies against fetal antigens
  • MAIPA- Monoclonal antibody specific immobilization of platelet antigens
• Platelet typing of parents and neonates by genotyping/ ELISA
• Cranial USG for IC bleed- Should be done in all cases

Treatment:

•  Start treatment even before confirmatory tests are available if platelets counts are less than 20,000/cmm
• Transfusion with HPA compatible/ HPA negative platelets if platelet count is <30,000/cmm or if there are bleeding complaints. Target platelet count- 50,000/cmm. Washed maternal platelets also can be used.
• If HPA negative/ compatible platelets are not available, any platelet can be given along with IVIg
• IVIg- 2gm/Kg- over 2-5 days. Effect is usually seen by 36 hrs. Useful if thrombocytopenia is prolonged. Mechanism of action is not clear.
• Steroids may be added
• Monitor platelet counts until there is a sustained rise in platelet count into normal range
• Prenatal treatment involves giving steroids and IVIg to mother and in utero transfusion of HPA negative platelets along with IVIg. This has to be done at specialized fetal medicine units.