1 Department of Obstetrics and Gynecology, The Affiliated Hospital of Inner Mongolia Medical University, Hohhot, Inner Mongolia, 010050, China.
2 Department of Obstetrics and Gynecology, The Affiliated Hospital of Inner Mongolia Medical University, Hohhot, Inner Mongolia, 010050, China. Electronic address: zhangruying1972@126.com.
3 Mongolia Medical University, Department of Orthopedics, Affiliated Hospital of Inner Mongolia Medical University, Hohhot North Street, Inner Mongolia, 010050, China.