1. Department of Obstetrics and Gynecology, Shandong Provincial Hospital Affiliated to Shandong First Medical University, Jinan, Shandong, P.R. China
2. Department of Obstetrics and Gynecology, Shandong Provincial Hospital, Shandong University, Jinan, Shandong, P.R. China
3. Department of Obstetrics and Gynecology, Liaocheng People’s Hospital, Liaocheng, Shandong, P.R. China
4. Department of Clinical Laboratory, The Laboratory of Placenta-related Diseases, Key Laboratory of Birth Regulation and Control Technology of National Health and Family Planning Commission of China, Jinan, Shandong, P.R. China