Objective To investigate the causes, clinical features and influence on mother and infant of thrombocytopenia in pregnancy in order to decrease maternal-infant bleeding during perinatal period. Methods Clinical data of 109 cases of thrombocytopenia during pregnancy from Nov 2001 to Jun 2008 in Obstetrics & Gynecology Hospital were reviewed retrospectively. Results Pregnancy-associated thrombocytopenia (PAT) is the major cause of thrombocytopenia in pregnancy. Twenty-one cases (19.3%) were diagnosed as immune or idiopathic thrombocytopenia purpura (ITP), in those 20 cases were pregnancy in combination with ITP and one case was pregnancy in combination with Evans’ syndrome. Five cases (4.6%) were diagnosed as hypertensive disorders during pregnancy, one of which was severe pre-eclampsia. Five infants (5.9%) experienced thrombocytopenia. There was no relation between hemorrhage in childbirth and the severity of thrombocytopenia. Conclusions PAT and ITP lead to most thrombocytopenia in pregnancy. The risk factors include histories of thrombocytopenia, allergy, viral infection and autoimmune diseases.