1. Department of Gynaecology
2. Xi'an Gaoxin Hospital
3. Xi'an 710000
4. China
5. Department of Gynaecology and Obstetrics
6. Yulin Second Hospital of Shaanxi Province
7. Yulin 719000
8. Baoji City Hospital Maternity and Child Health Care Hospital
9. Baoji 721000
10. Obstetrical Department
11. Shaanxi Baoji Maternal and Child Health Hospital
12. Ankang City Central Hospital
13. Ankang 725000
14. Yanan University Affiliated Hospital
15. Yanan 716000