1 Department of Obstetrics and Gynecology, Hebei Yanda Hospital, Affiliated Hebei Medical University, Yanda International Health City, Sipulan Road, Yanjiao Economic and Technological Development Zone, Sanhe, Hebei Province, China.
2 Department of Obstetrics and Gynecology, China Meitan General Hospital/Emergency General Hospital, Beijing, China.
3 Department of Obstetrics and Gynecology, Beijing Fengtai Hospital, Affiliated Capital Medical University, Beijing, China.
4 Wangjing Hospital, China Academy of Chinese Medical Sciences, Beijing, China.