Chinese Academy of Medical Sciences - Department of Obstetrics and Gynecology, Hebei Medical University - Department of Obstetrics and Gynecology, Tangshan Maternal and Child Health Hospital - Department of Obstetrics and Gynecology, Henan Provincial People's Hospital - Department of Obstetrics and Gynecology, Guangzhou Medical University - Third Affiliated Hospital Department of Obstetrics and Gynecology, Huazhong University of Science and Technology - Department of Obstetrics and Gynecology, Xiamen University - First Affiliated Hospital, Department of Obstetrics and Gynecology, Guangzhou Women and Children's Medical Center - Department of Gynecology, Liuzhou Maternity and Child Healthcare Hospital - Department of Obstetrics and Gynecology, Anhui Medical University - Second Affiliated Hospital, Department of Obstetrics and Gynecology, Tibet Autonomous Region People’s Hospital - Department of Obstetrics and Gynecology, Zhengzhou University - Department of Obstetrics and Gynecology, Guangxi Medical University - Department of Obstetrics and Gynecology, Nantong University - Department of Obstetrics and Gynecology, Peking University - Third Hospital, Department of Obstetrics and Gynecology, Harbin Medical University - First Affiliated Hospital. Department of Obstetrics and Gynecology, Capital Medical University - Beijing Ditan Hospital, Department of Obstetrics and Gynecology, Capital Medical University - Xuanwu Hospital Department of Obstetrics and Gynecology, Capital Medical University - Beijing Anzhen Hospital, Department of Obstetrics and Gynecology, Inner Mongolia People’s Hospital - Department of Obstetrics and Gynecology, Capital Medical University - Beijing Chaoyang Hospital, Department of Obstetrics and Gynecology, Harbin Medical University - Department of Obstetrics and Gynecology, Chinese Academy of Medical Sciences - Department of Epidemiology and Statistics and Chinese Academy of Medical Sciences - Department of Obstetrics and Gynecology