1. Department of Obstetrics, The Second Hospital, Cheeloo College of Medicine, Shandong University, No. 247 Beiyuan Road, Tianqiao District, Jinan, Shandong Province, China
2. Department of Obstetrics, Jining First People’s Hospital, No. 6 Jiankang Road, Rencheng District, Jining, Shandong Province, China