New SBA questions on Fetal Neonatal Alloimmune Thrombocytopenia (FNAIT)

A 28-year-old Gravida 2, Para 1 woman is referred for consultant led antenatal care at 12 weeks gestation. In her first pregnancy, her baby was diagnosed antenatally with a right-sided intraventricular haemorrhage at 32 weeks gestation causing severe ventriculomegaly. Her first child was born at 37 weeks by planned Caesarean section with a platelet count of 6 × 10⁹/L and required multiple platelet transfusions. Subsequent investigations confirm a diagnosis of fetal neonatal alloimmune thrombocytopenia (FNAIT) with high-titre maternal anti-HPA antibodies.  What HPA antigen is most commonly associated with FNAIT?

A 28-year-old Gravida 2, Para 1 woman is referred for consultant led antenatal care at 12 weeks gestation. In her first pregnancy, her baby was diagnosed antenatally with a right-sided intraventricular haemorrhage at 32 weeks gestation causing severe ventriculomegaly. Her first child was born at 37 weeks by planned Caesarean section with a platelet count of 6 × 10⁹/L and required multiple platelet transfusions. Subsequent investigations confirm a diagnosis of fetal neonatal alloimmune thrombocytopenia (FNAIT) with high-titre maternal anti-HPA-1a antibodies.  Maternal HPA testing confirmed that she has a HPA-1b-1b phenotype. Paternal HPA testing confirmed that her partner has a homozygous HPA-1a-1a phenotype.  What is the chance of the current pregnancy being affected by FNAIT?