1. Department of Gynaecology and Obstetrics, Xian XD Group Hospital, Xi’an 710077, Shanxi, China
2. Department of Gynaecology and Obstetrics, Affiliated Huxi Hospital of Jining Medical College, Shanxian County, Heze 274300, Shandong, China
3. Department of Gynaecology, Maternal and Child Health Hospital of Tangshan, Tangshang 063000, Hebei, China