1. Department of Basic Medicine, Ningxia Medical University, Yinchuan, Ningxia 750004, P.R. China
2. Department of Prenatal Diagnosis Center, General Hospital of Ningxia Medical University, Yinchuan, Ningxia 750004, P.R. China
3. Department of Infectious Disease, General Hospital of Ningxia Medical University, Yinchuan, Ningxia 750004, P.R. China