[1] Tianjin Med Univ, Sch Nursing, 22 QiXiangTai Rd, Tianjin 300070, Peoples R China
[2] Peking Univ, Sch Nursing, 38 Xueyuan Rd, Beijing 100083, Peoples R China
[3] Peking Univ Third Hosp, Dept Obstet & Gynecol, 49 North Huayuan Rd, Beijing 100083, Peoples R China
[4] Tianjin Med Coll, Dept Nursing, 14 Liulin Rd, Tianjin 300222, Peoples R China