Abstract： Objective To investigate the etiology and perinatal outcome of pregnancies complicated with extremely severe thrombocytopenia [ at least two times of platelets count (PLT) < 10 × 109/L during pregnancy]. Methods Clinical data, including basic information, etiology, management and outcomes of pregnant women with extremely severe thrombocytopenia, admitted to Peking University People's Hospital from January 2004 to March 2009, were retrospectively collected. The management of these cases varied according to different etiology and the symptoms: (1) PLT were maitained > 20 × 109/L and hemoglobulin> 70 g/L in those women without spontaneous bleeding; (2) PLT transfusion would be required when PLT< 10 × 109/L or bleeding occur and RBC would be supplied when hematocrit <25% and hemoglobulin <70g/L; (3) Hemoglobulin should be > 70 g/L and PLT >30 × 109/L before cesarean section or delivery;(4) Predinisone and/or intravenous immunoglobulin G (IVIG) would be given in women complicated with idiopathic thrombocytopenic purpura (ITP) when PLT < (20-30) × 109/L or bleeding. PLT would be given if all the above management were failed, or PLT < 10 × 109/L, or bleeding. Women without bleeding would be closely monitored and delivery would be planned. Results (1) Twenty-six cases were identified among 9302 deliveries during the study period (0.28%), with an average of maternal age of 29. Seventeen were diagnosed before conception and 9 during pregnancy. Among the 26 women, half received regular prenatal check in our hospital and the average gestations at diagnosis was 24 weeks and the other half without regular prenatal visits and the average gestations at diagnosis was 32 weeks. Etiology was identified in 24 out of the 26 women, including 14(54%) ITP, 5 myelodysplastic syndrome (MDS), 4 chronic aplastic anaemia(CAA) and 1 systemic lupus erythematosus (SLE). (2) Management: All of the 26 women received blood products. Among the 14 ITP cases, 6 received predinisone and IVIG and 8 only took predinisone. Nine of the 26 patients (35%) had pregnant complications, among which 6 (6/9) were preeclampsia. The overall average gestation at delivery was 36 weeks. Only 2 delivered vaginally with the average blood loss of 83 ml and 23 cesarean sections were performed with the average blood loss of 410 ml. (3) Perinatal outcomes:There were 26 perinatal babies, among which 1 died intrauterine and 25 were born alive (12 preterm infants). The average birth weight was 2877 g. Neonatal severe thrombocytopenia presented in 2 newborns whose mother complicated with ITP. Conclusions The main cause of extremely severe thrombocytopenia during pregnancy is ITP, managed mainly by predinisone and IVIG, followed by CAA and MDS, which may require supportive treatment. Pregnancy complicated with extremely severe thrombocytopenia is not an indication of termination. Better maternal and fetal outcomes can be achieved through proper treatment based on the etiology, intensive care in prevention and management of complications and cesarean section.