Background & objectives: Thrombocytopeniais, defined as a platelet count of less than 150,000/L complicates 7 to 10% of all pregnancies. Etiology of thrombocytopenia in pregnancy may include a ranging from benign disorders such as gestational thrombocytopenia to life threatening syndromes such as the HELLP (Hemolysis, Elevated liver Enzymes, Low Platelet count). The aim of this study was to evaluate frequency of thrombocytopenia in pregnancy among pregnantsrefered to Tonekabon health centers during 2009 .

  Methods: In a cross-sectional study, 150 normal pregnants bearing third trimester and refered to Tonekabon health centers were selected by random simple sampling. Patients´ demographic information and history were obtaied and CBC (complete blood count) test was done. Those pregnants suffered from thrombocytopenia were refered to a hematologist for compeleting tests if needed. Data analysis was done by SPSS 11.5 and chi-square test and p<0.05 was considered as signifcant difference .

  Results: The Prevalence of thrombocytopenia in pregnancy was 12.66% and the highest percent of thrombocytopenia (68%) was observed among nullipars. The cause of 95% of thrombocytopenia in pregnancy was gestational thrombocytopenia and 5% were due to ITP (Idiopathic Thrombocytopenia Purpura). The pregnants who suffered from gestational thrombocytopenia didn’t have any problems and no need to treatment but those who had been experienced ITP, used venous immunoglobin during labor for treatment .

  Conclusion: Gestational thrombocytopenia is the most common cause of the thrombocytopenia in pregnancy and isn’t dangerous for mother and fetus. So, it is no need to be done any intervention .