1. Department of Obstetrics and Gynecology, The First Affiliated Hospital of Xi'an Jiaotong University, Xi'an, Shaanxi 710061, P.R. China
2. Department of Obstetrics and Gynecology, Renmin Hospital of Wuhan University, Wuhan, Hubei 430060, P.R. China
3. Department of Gastroenterology, Third People's Hospital of Xiantao in Hubei Province, Xiantao, Hubei 433000, P.R. China