Clinical features

• Commonly presents in first born infant and recurs in 85-90%.

• Maternal platelet count normal with no past history of ITP.

• Bleeding manifestations in 10-20% evident within the first few days of life e.g. umbilical haemorrhage, petechiae, ecchymosis, internal haemorrhage, intracranial haemorrhage (ICH).

• Baby's platelet count 4 to normal over the next 2-3 weeks as the antibody is cleared.

• Haemorrhage in utero with fatal ICH in ~1% cases.

Laboratory diagnosis Baby

Severe thrombocytopenia platelets <20 x 109/L in 50% BM has megakaryocytes ++ (not usually necessary)

Parents

Mother's platelet count normal Serology

Mother's platelets usually HPA-1a -ve Rarer Ab include anti-HPA-3a, HPA-5b, HPA-4 (Yuk/Pen) Mother's serum contains anti-platelet antibody

(Note: antibody titre cannot predict degree of thrombocytopenia in fetus in subsequent pregnancies) Father's platelets carry offending antigen

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