1. Hui-Ling Xue:
Department of Obstetrics and Gynecology, Affiliated Hospital of Hebei University, Baoding, Hebei Province, P. R. China
2. Ning Yu:
Department of Obstetrics and Gynecology, People’s Hospital of Yi County, Baoding, Hebei Province, P. R. China
3. Jing Wang:
Department of Obstetrics and Gynecology, Affiliated Hospital of Hebei University, Baoding, Hebei Province, P. R. China
4. Wan-Jiao Hao:
Department of Obstetrics and Gynecology, Affiliated Hospital of Hebei University, Baoding 071000, Hebei Province, P. R. China
5. Ye Li:
Department of Obstetrics and Gynecology, Affiliated Hospital of Hebei University, Baoding 071000, Hebei Province, P. R. China
6. Mei-Yun Liu:
Department of Obstetrics and Gynecology, Affiliated Hospital of Hebei University, Baoding 071000, Hebei Province, P. R. China