1. Department of Pediatrics, West China Second University Hospital, Key Laboratory of Obstetric & Gynecologic and Pediatric Diseases and Birth Defects of Ministry of Education, Sichuan University, Chengdu, China
2. Department of Ultrasonic, West China Second University Hospital, Sichuan University, Chengdu, China
3. Evidence Based Social Science Research Center, School of Public Health, Lanzhou University, Lanzhou, China