1. Department of Pediatrics, West China Second University Hospital, Sichuan University, Chengdu, China
2. Key Laboratory of Obstetrics and Gynecologic and Pediatric Diseases and Birth Defects of the Ministry of Education, Sichuan University, Chengdu, China
3. Department of General Practice, West China Hospital, Sichuan University, Chengdu, China
4. Department of Obstetrics and Gynaecology, West China Second University Hospital, Sichuan University, Chengdu, Sichuan, China
5. Ultrasonic Department, West China Second University Hospital, Sichuan University, Chengdu, China