1. School of Medicine, Shandong University, Jinan, Shandong 250012, P.R. China
2. Department of Obstetrics and Gynecology, Provincial Hospital Affiliated to Shandong University, Jinan, Shandong 250021, P.R. China
3. Center for Reproductive Medicine, Reproductive Hospital Affiliated to Shandong University, Jinan, Shandong 250021, P.R. China
4. Key Laboratory of Birth Regulation and Control Technology of National Health Commission of China, Maternal and Child Health Care Hospital of Shandong Province, Shandong University, Jinan, Shandong 250001, P.R. China