1. Department of Obstetrics and Gynecology, Shandong Provincial Third Hospital, Cheeloo College of Medicine, Shandong University, Jinan, Shandong 250001, P.R. China
2. Department of Obstetrics and Gynecology, Jinan Maternity and Child Care Hospital, Jinan, Shandong 250001, P.R. China
3. Department of Clinical Laboratory, Jinan Maternity and Child Care Hospital, Jinan, Shandong 250001, P.R. China