Phase 2 Study on the Pharmacokinetics and Safety of RLYB212 in Pregnant Women at Higher Risk for HPA-1a Alloimmunization

Inclusion Criteria: Pregnant women who present at Gestational Week 6 or after and confirmed to be: HPA-1b/b (HPA-1a negative), HLA-DRB3\*01:01 positive, Anti-HPA-1a alloantibody negative, Carrying an HPA-1a/b (HPA-1a positive) fetus Exclusion Criteria: * Prior history of HPA-1a related fetal and neonatal alloimmune thrombocytopenia * Multiple pregnancy (more than 1 fetus) * Prior history of platelet transfusion or other blood transfusions * Known sensitivity and/or immediate hypersensitivity to any components of RLYB212 or its formulation * Any co-morbid medical or obstetric condition(s), laboratory abnormality, concomitant treatment, or other reason that, in the investigator's opinion, could adversely affect the safety of the participant and/or fetus, impair the assessment of study results, or preclude compliance with the study