1. Department of Obstetrics and Gynecology, The Fourth Affiliated Hospital of Harbin Medical University, Harbin, Heilongjiang 150001, P.R. China
2. Gastroenterology Department, Harbin The First Hospital, Harbin, Heilongjiang 150001, P.R. China
3. Department of Obstetrics and Gynecology, The Hospital of Heilongjiang, Harbin, Heilongjiang 150001, P.R. China