1. Department of Gynaecology, Panzhihua Maternal and Child Health Hospital (Panzhihua Women & Children Hospital), Panzhihua City, Sichuan Province, China
2. Department of Gynaecology, Hainan General Hospital, Haikou City, Hainan Province, China
3. Department of Obstetrics, Taian Central Hospital, Taian City, Shandong Province, China
4. Department of Gynaecology, Renmin Hospital, Hubei University of Medicine, Shiyan, Hubei, China