1. Department of Obstetrics and Gynecology, The Second Affiliated Hospital of Harbin Medical University, Harbin, Heilongjiang 150086, P.R. China
2. Department of Obstetrics and Gynecology, Beijing Friendship Hospital, Capital Medical University, Beijing 100050, P.R. China
3. Department of Neurobiology, Harbin Medical University, Harbin, Heilongjiang 150086, P.R. China