1. Ningxia Medical University, General Hospital of Ningxia Medical University, Yinchuan, Ningxia, China
2. Reproductive Medicine Center, Yinchuan Maternal and Child Health Hospital, Yinchuan, Ningxia, China
3. Gansu Province Maternity and Child-care hospital, Lan zhou, Gansu, China
4. Reproductive Medicine Center, Key Laboratory of Fertility Preservation and Maintenance of Ministry of Education, Ningxia Medical University, General Hospital of Ningxia Medical University, Yinchuan, Ningxia, China