Authors’ contributations
Guan Nan Zhou: data management and analysis, draft manuscript. Yuan Yuan Gu: extract raw data, draft manuscript. Qing Wang: review medical cord and data extraction at Department of Gynecology, the Obstetrics and Gynecology Hospital of Fudan University, read and edit manuscript. Ke Qin Hua: review medical cord and data extraction at Department of Gynecology, the Obstetrics and Gynecology Hospital of Fudan University, read and edit manuscript. Jing Xin Ding: review medical cord and data extraction at Department of Gynecology, the Obstetrics and Gynecology Hospital of Fudan University, read and edit manuscript.