The etiology of serious thrombocytopenia during pregnancy is various. The evaluation and management should base on the etiology of thrombocytopenia. The common internal medical causes of severe thrombocytopenia during pregnancy include idiopathic thrombocytopenic purpura, acute leukemia, aplastic anemia, myelodysplastic syndromes, and systemic lupus erythematosus. During pregnancy, HELLP syndrome, thrombotic thrombocytopenic purpura and postpartum hemolytic uremic also can induce the severe thrombocytopenia. This article discusses classification, evaluation and management of thrombocytopenia in pregnancy.