1. Department of Obstetrics and Gynecology, The Second Affiliated Hospital of Dalian Medical University, Dalian, Liaoning, China
2. Department of Obstetrics and Gynecology, Beijing Hospital, National Center of Gerontology; Institute of Geriatric Medicine, Chinese Academy of Medical Science, Beijing, China
3. Peking Union Medical College, Chinese Academy of Medical Sciences, Graduate School of Peking Union Medical College, Beijing, China
4. Department of Pathology, The Second Affiliated Hospital of Dalian Medical University, Dalian, Liaoning, China