1. First Gynecological Ward, Binzhou People's Hospital, Binzhou, Shandong 256610, P.R. China
2. Department of Health Checkup, Binzhou People's Hospital, Binzhou, Shandong 256610, P.R. China
3. Department of Nursing, Shandong Medical College, Jinan, Shandong 250002, P.R. China