Isoimmunization to platelet antigen HPA-1a and the placental transfer of maternal antibodies would be expected to cause newborn:

Isoimmunization to the platelet antigen HPA-1a occurs when a mother produces antibodies against this specific antigen present on the platelets of the fetus, which may arise following pregnancy complications or blood transfusions that involve antigens to which the mother has not been previously exposed. Because maternal antibodies can cross the placenta, they can target fetal platelets, leading to a condition known as neonatal alloimmune thrombocytopenia (NAIT).

In cases of NAIT, the fetal platelets are destroyed by the maternal antibodies, resulting in a decreased platelet count in the newborn, a condition referred to as thrombocytopenia. This is critical because low platelet counts can lead to increased risk of bleeding and other associated complications in the newborn.

While other conditions like erythroblastosis involve the destruction of red blood cells due to different immunologic mechanisms, the specific involvement of HPA-1a antigen and maternal antibodies leads directly to thrombocytopenia rather than affecting white blood cells or red blood cells. Therefore, the newborn would be expected to experience thrombocytopenia as a result of isoimmunization to platelet antigen HPA-1a.