1. Department of Obstetrics, The Second Hospital of Shandong University, Jinan, Shandong, P.R. China
2. Department of Digestive Disease, The Second Hospital of Shandong University, Jinan, Shandong, P.R. China
3. Central Laboratory, Institute of Medical Science, The Second Hospital of Shandong University, Jinan, Shandong, P.R. China