Fetal/neonatal alloimmune thrombocytopenia (FNAIT) can be a cause of severe fetal thrombocytopenia, with the common presentation being intracranial hemorrhage in the fetus, usually in the third trimester. A very unusual case of fetal anemia progressed to hydrops. This was further complicated by maternal Mirror syndrome and human chorionic gonadotropin-induced thyrotoxicosis. Without knowledge of etiology, and possibly due to associated cardiac dysfunction, fetal transfusion resulted in fetal demise. Subsequent testing revealed FNAIT as the cause of severe hemorrhagic anemia. In cases with fetal anemia without presence of red blood cell antibodies, FNAIT must be ruled out as a cause prior to performing fetal transfusion. Fetal heart may adapt differently to acute hemorrhagic anemia compared with a more subacute hemolytic anemia.