gestational thrombocytopenia. Thrombocytopenia occurring during pregnancy (usually less than 70,000 platelets/mm3). Serious illnesses that cause low platelet counts (such as disseminated intravascular coagulation, HELLP syndrome, idiopathic thrombocytopenic purpura, preeclampsia, systemic lupus erythematosus, or leukemia) should be ruled out.