Abstract: Objective: To study the etiology and its influence on the mother and infant of severe pregnancy thrombocytopenia. Methods: The clinical data of 37 cases of severe pregnancy thrombocytopenia were analyzed retrospectively. The cases were divided into two groups according to the causes of the disease. The cases with pregnancy-associated thrombocytopenia(PAT) were enrolled in group Ⅰ and the cases with idiopathic thrombocytopenic purpura(ITP),aplastic anemia,HELLP syndrome and myelodysplasia(MDS-RA) in groupⅡ. The outcome was compared between the two groups. Results: Twenty-three cases(62.3%) of severe thrombocytopenia during pregnancy were caused by PAT,and 9 cases(24.32%) were caused by ITP. The incidence of postpartum hemorrhage in groupⅡ was markedly higher than that in group Ⅰ(P < 0.05). The neonate's average birth weight in group Ⅰwas higher than that in group Ⅱ,and the average gestational age of groupⅠwas senior to that of group Ⅱ(P < 0.05-P < 0.01). The platelet counts in groupⅠ recovered more quickly than that in group Ⅱ 10 days after the operation(P < 0.01). Conclusions: The major causes of severe thrombocytopenia during pregnancy are PAT and ITP; however,the patients suffering from PAT have a better outcome.