Xinghui Liu1, Tao Duan, Qing Chang, Jin He, Meng Chen, Li Zhang. 1. Department of Obstetrics and Gynecology, West China Second University, Hospital of Sichuan University, Chengdu, China Department of Obstetrics and Gynecology, Shanghai First Maternity and Infant, Hospital of Tongji University, Shanghai, China Department of Obstetrics and Gynecology, Southwest Hospital of Third Military, Medical University, Chongqing, China Department of Obstetrics and Gynecology, Women's Hospital School of Medicine, of Zhejiang University, Hangzhou, China Department of Obstetrics and Gynecology, West China Second University, Hospital of Sichuan University, Chengdu, China.