1 Department of Obstetrics, The Affiliated Hospital of Southwest Medical University, Luzhou, China.
2 Department of Obstetrics and Gynecology, Union Hospital, Tongji Medical College, Huazhong University of Science and Technology, Hubei, China.
3 Department of Obstetrics and Gynecology, Union Hospital, Tongji Medical College, Huazhong University of Science and Technology, Hubei, China. xiehezouli@hust.edu.cn.