Corresponding Author

Xiaowei Liu

Department of Obstetrics, Beijing Obstetrics and Gynecology Hospital, Capital Medical University, Beijing Maternal and Child Health Care Hospital, Beijing, China

Correspondence: Xiaowei Liu, Beijing Obstetrics and Gynecology Hospital, Capital Medical University, Beijing Maternal and Child Health Care Hospital, 251# Yaojiayuan Road, Chaoyang, Beijing 100026, China.

Email: liuxiaowei@mail.ccmu.edu.cn, doctorliuxiaowei@163.com