1. Department of Gynecology and Obstetrics, The First Affiliated Hospital of Xinxiang Medical University,Weihui, Henan 453100, P.R. China
2. Department of Gynecology and Obstetrics, Maternal and Child Health Hospital ofZhengzhou City, Zhengzhou, Henan 450012, P.R. China
3. Department of Gynecology and Obstetrics, Maternal and ChildHealth Hospital of Fangcheng County, Nanyang, Henan 473200, P.R. China