1. Department of Obstetrics and Gynecology, The First Affiliated Hospital of Jiamusi University, Heilongjiang Province 154002, P.R. China
2. Department of Anesthesiology, The First Affiliated Hospital of Jiamusi University, Heilongjiang Province 154002, P.R. China
3. Department of Gynaecology and Obstetrics, People’s Hospital of Zoucheng, Jining 273500, Shandong Province, P.R. China