Author Affiliations:
1. Department of First Clinical Medical College, Shanxi Medical
University, Taiyuan, China;
2. Department of Obstetrics, First Hospital of Shanxi Medical
University, Taiyuan, China.
*Corresponding author: Prof. Dr.
Hailan Yang, Taiyuan, Shanxi Province, China; Telephone:
+86-13834048059; E-mail:feichihai@sina.com.