We report a case of prenatally diagnosed intracranial hemorrhage and hydrops in the fetus of a mother with a past history of surgical and medical treatment for gastric lymphoma and having high platelet counts thereafter. To the best of our knowledge, such a complication of maternal thrombocythemia has not been described in the literature. In our opinion, the possible pathophysiology of the disease is based on placental insufficiency due to infarctions and related fetal platelet dysfunction, leading to intracranial hemorrhage with subsequent hydrops fetalis. The trigger in this event appears to be trauma to the maternal abdomen. Certain measures for high-risk mothers such as avoidance of trauma to the abdomen and platelet-lowering medications like interferon-α may be useful for preventing such fetal complications.