[1] Hebei Med Univ, Sch Nursing, Shijiazhuang, Peoples R China
[2] Peking Univ, Sch Nursing, Beijing 100191, Peoples R China
[3] Hebei Med Univ, Dept Obstet & Gynaecol, Affiliated Hosp 4, Shijiazhuang, Peoples R China
[4] Hebei North Univ, Dept Nursing, Affiliated Hosp 1, Zhangjiakou, Peoples R China
[5] Peking Univ First Hosp, Dept Nursing, Beijing, Peoples R China
[6] Beijing Hosp, Dept Obstet, Beijing, Peoples R China
[7] Peking Univ Peoples Hosp, Dept Obstet, Beijing, Peoples R China