1. Department of Obstetrics and Gynecology, Nanfang Hospital, Southern Medical University, Guangzhou, China.
2. Department of Obstetrics and Gynecology, The Fourth Hospital of Hebei Medical University, Shijiazhuang, China.
3. Department of Obstetrics and Gynecology, Xijing Hospital, Air Force Military Medical University, Xi’an, China.
4. Department of Obstetrics and Gynecology, the First Affiliated Hospital of Zhengzhou University, Zhengzhou, China.