Subsequent pregnancy after a previous child with FNAIT-related intracranial haemorrhage — structured SAQ (15 marks)

(a) Pathophysiology and commonest antibody (2 marks)

One mark for the pathophysiology, one for the antibody. ^[1]

• Pathophysiology: FNAIT is the platelet equivalent of haemolytic disease of the fetus and newborn — maternal IgG alloantibody against a paternally inherited fetal human platelet antigen crosses the placenta and is cleared by the fetal reticuloendothelial system along with the antibody-coated fetal platelets, producing isolated fetal and neonatal thrombocytopenia.^[1]
• Commonest antibody: anti-HPA-1a is the commonest implicated antibody in people of European ancestry — the most immunogenic antigen.^[1]

(b) Antenatal management — agent, dose, timing, monitoring (5 marks)

One mark each for the agent, the dose, the timing, the monitoring, and the risk-stratified rationale. ^[6]

• Agent: maternal intravenous immunoglobulin (IVIG), the cornerstone of antenatal FNAIT treatment.^[6]
• Dose: high-dose IVIG — 1 to 2 g/kg per week — for this high-risk pregnancy (a previous child with antenatal intracranial haemorrhage).^[6]
• Timing: commenced at 12 to 18 weeks' gestation for the high-risk pregnancy (standard-risk FNAIT, a previous child without ICH, would commence at 20 to 28 weeks).^[6]
• Monitoring: weekly IVIG administration, weekly ultrasound surveillance for intracranial haemorrhage, and selected fetal blood sampling (cordocentesis) where the count is needed to guide escalation — reserved, not routine, because of the procedure-related fetal loss rate.^[1][6]
• Risk-stratified rationale: the Bussel 2010 stratified-management study addressed the highest-risk scenario (37 pregnancies with a previous child ICH). Treatment began at 12 weeks with IVIG 1 or 2 g/kg per week; five of 37 fetuses suffered ICH, but only two were unequivocal treatment failures. Stratified treatment reduced, but did not eliminate, recurrent ICH — so escalation with prednisolone is added when the response is inadequate.^[6]

(c) Mode of delivery and perinatal preparations (3 marks)

One mark each for the mode, the principle, and the perinatal preparations. ^[1][9]

• Mode of delivery: caesarean section — the lowest threshold for caesarean, on the principle of minimising birth trauma to a potentially severely thrombocytopenic fetus.^[1]
• Principle: the fetus at risk of severe thrombocytopenia must not be exposed to the mechanical stress of operative vaginal delivery or fetal scalp electrode placement. The threshold for caesarean is set locally based on the fetal count where known (commonly under 50 to 100 × 10⁹ per L).^[1][6]
• Perinatal preparations: plan delivery at a centre with neonatal and paediatric haematology support, with HPA-compatible or HPA-1a-negative platelets available for the neonate, and alert the neonatal team before birth.^[9]

(d) Neonatal management, follow-up and registry outcome (5 marks)

One mark each for confirmation, platelet transfusion, the increment evidence, the cranial imaging, and the registry outcome. ^[1][9]

• Confirmation: platelet count; anti-HPA antibody confirmation; HPA typing of the neonate; maternal and paternal HPA typing.^[9]
• Platelet transfusion: HPA-matched or HPA-1a-negative platelets for severe thrombocytopenia or bleeding. The international postnatal cohort documented a median platelet increment of 98 × 10⁹ per L after HPA-matched transfusion versus 59 × 10⁹ per L after HPA-unmatched transfusion — the matched product is preferred wherever available.^[9]
• Cranial imaging: cranial ultrasound for intracranial haemorrhage in every affected neonate, and developmental follow-up after an ICH (cerebral palsy, intellectual impairment, epilepsy).^[9]
• Registry outcome: the international NOICH registry of 615 pregnancies reported intracranial haemorrhage in 23 fetuses or neonates (3.7%) and overall perinatal mortality of 1.1% (7 of 615). Over the registry period, management shifted from invasive to non-invasive in most centres.^[1]
• Long-term follow-up: serial platelet counts until a safe plateau; developmental surveillance; and pre-pregnancy counselling before the next pregnancy.^[1][9]