Department of Obstetrics and Gynecology, Women's Hospital, School of Medicine, Zhejiang University, Hangzhou, Zhejiang 310006,China;
Department of Gynecology, West China Second University Hospital, Sichuan University, Chengdu, Sichuan 610041, China;
Department of Gynecology, Affiliated Hospital of Qingdao University, Qingdao, Shandong 266003, China;
Department of Gynecology, Hubei Maternity and Child Health Hospital, Wuhan, Hubei 430070, China;
Department of Family Planning, Changzhou Maternal and Child Health Care Hospital, Changzhou, Jiangsu 213003, China;
Department of Gynecology, Kunming City Maternal and Child Health Hospital, Kunming, Yunnan 650031, China;
Department of Family Planning,Beijing Obstetrics and Gynecology Hospital,Capital Medical University,Beijing 100026,China;
