1. Department of Obstetrics and Gynecology; Central Hospital of Enshi Tujia and Miao Autonomous Prefecture; Enshi Clinical College of Wuhan University; Enshi Hubei 445000 P.R. China
2. Department of Obstetrics and Gynecology, Tongji Hospital; Tongji Medical College, Huazhong University of Science and Technology; Wuhan Hubei 430030 P.R. China
3. Department of Reproductive Medicine; Zigong Maternity and Infant Healthcare Hospital; Zigong Sichuan 643000 P.R. China
4. Department of Obstetrics and Gynecology; Hubei Province Maternity and Child Health Care Hospital; Wuhan Hubei 430030 P.R. China