Neonatal anaemia, polycythaemia and thrombocytopenia: SAQ

Part A (10 marks)

a) What is the most likely diagnosis, and what is the underlying pathophysiology? (3 marks) ^[2]

The most likely diagnosis is fetal and neonatal alloimmune thrombocytopenia: isolated severe thrombocytopenia at birth in an otherwise well term infant, a normal maternal platelet count, and a previously affected sibling. Maternal immunoglobulin G against a paternally inherited human platelet antigen (most often HPA-1a in European ancestry) crosses the placenta and destroys fetal platelets. Clinically apparent immunisation usually occurs in the first pregnancy. ^[3]

b) What immediate investigation is required, and why? (2 marks) ^[3]

Cranial imaging for intracranial haemorrhage is required urgently in every newborn with suspected fetal and neonatal alloimmune thrombocytopenia, regardless of the current platelet count. Haemorrhage may be clinically silent. ^[3]

c) Outline the immediate management, including the blood product of choice. (3 marks) ^[2]

Transfuse platelets without delay. HPA-selected (typically HPA-1a-negative) units are preferred if immediately available. If they are not, unselected platelets should be transfused; a matched-donor search must not postpone the first transfusion. Optimal volume (10 versus 20 mL per kg) is unknown. Postnatal intravenous immunoglobulin alone, or added to platelets, does not provide additional therapeutic benefit. For life-threatening bleeding, target at least 100 times 10 to the 9 per litre initially. ^[3]

d) What should parents be told about subsequent pregnancies, and what antenatal intervention is offered? (2 marks) ^[2]

Severe thrombocytopenia is expected in the majority of subsequent pregnancies if the fetus inherits the antigen. After a previous intracranial haemorrhage, one series reported recurrence in 11 of 13 cases. Offer antenatal intravenous immunoglobulin in subsequent affected pregnancies: as early as 12 weeks after previous haemorrhage (Lieberman), commonly 1 g per kg per week from 20 to 24 weeks (Sachs). ^[3]