1. Department of Gynecology, Beilun People's Hospital, Beilun Branch of the First Affiliated Hospital, School of Medicine, Zhejiang University, Ningbo, Zhejiang 315826, P.R. China
2. Department of Obstetrics, Beilun People's Hospital, Beilun Branch of the First Affiliated Hospital, School of Medicine, Zhejiang University, Ningbo, Zhejiang 315826, P.R. China