HPSE and alloimmunization: HPA-associated alloimmunization in first pregnancies is not uncommon.6, 7One study showed 63% of severe FNAIT cases occurred in first-time pregnancies, with worsening outcomes when clinical features of FNAIT appeared at an earlier gestational age.6The mechanism of alloimmunization is not well understood; however, HPA-1a antigens are also expressed on placental trophoblast cells, a possible source of alloimmunization.8