Prenatal treatment of fetomaternal thrombocytopenia

Abstract

A 34-year old Caucasian woman (gravida 2, para 1) with a history of fetomaternal alloimmune thrombocytopenia presented for antenatal care in her second pregnancy at 12 weeks' gestation. Her first baby was severely affected by fetomaternal alloimmune thrombocytopenia (platelet count < 3×109/litre) and presented with neonatal purpura and fits caused by intracranial haemorrhage. Fetomaternal platelet incompatibility and presence of maternal anti-HPA-1b antibodies was demonstrated (Table 1) and the baby treated successfully, with platelet transfusions (HPA-1 negative). During her second pregnancy, the mother's booking platelet count was 250 × 109/litre. Fetal platelet typing via amniocentesis at 16 weeks showed fetal platelet genotype HPA 1a1b. The modified direct monoclonal antibody-specific immobilization of platelet antigens (MAIPA) test showed that the mother was still positive for anti-HPA-1b antibodies (Table 1), indicating a high risk of fetomaternal alloimmune thrombocytopenia in this pregnancy. Starting at 16 weeks, she received weekly intravenous immunoglobulin 1 g/kg. The anomaly scan at 20 weeks was unremarkable. Further monitoring included weekly cranial scans to detect intracranial haemorrhage, and monthly growth scans. These were all normal. The mother declined fetal blood sampling to assess the fetal platelet count. Steroids were given at 33 weeks and baby delivered by planned caesarean section at 34 weeks. The boy weighed 2.75 kg and had no signs of bleeding. His platelet count was 100 × 109/litre and he has been well since.