1. Department of Pediatric Surgery, Hongqi Hospital Affiliated to Mudanjiang Medical University, Mudanjiang, Heilongjiang 157000, P.R. China
2. Department of Gynaecology and Obstetrics, Second Affiliated Hospital of Mudanjiang Medical University, Mudanjiang, Heilongjiang 157000, P.R. China
3. Department of Gynaecology and Obstetrics, Hongqi Hospital Affiliated to Mudanjiang Medical University, Mudanjiang, Heilongjiang 157000, P.R. China