1. Department of Gynaecology, The Fifth Affiliated Hospital of Xinjiang Medical University, Urumqi, Xinjiang Uygur Autonomous Region 830011, P.R. China
2. Department of Reproductive Medicine, Hainan West Central Hospital, Danzhou, Hainan 571799, P.R. China
3. Department of Obstetrical and Gynecology, Hainan Modern Women and Children's Hospital, Haikou, Hainan 570300, P.R. China