1. Clinical Skills Training Center, Henan University of Chinese Medicine, Zhengzhou, Henan 450046, P.R. China
2. Perinatal Care Division, Beijing Obstetrics and Gynecology Hospital, Capital Medical University, Beijing Maternal and Child Health Care Hospital, Beijing 100026, P.R. China
3. Obstetrics and Gynecology, Second Affiliated Hospital of Shaanxi University of Chinese Medicine, Xianyang, Shaanxi 712000, P.R. China