Institution: | 1.Department of Obstetrics and Gynecology, Beijing Tiantan Hospital, Capital Medical University, No. 119 South Fourth Ring West Road, Fengtai District, Beijing, 100070 P.R. China ;2.Department of Obstetrics and Gynecology, Shunyi Maternal and Children’s Hospital of Beijing Children’s Hospital, Beijing, 101300 P.R. China |