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.