1. Department of Ultrasonography, West China Women and Children Hospital Affiliated to Sichuan University, Chengdu, Sichuan 610041, P.R. China
2. Key Laboratory of Birth Defects and Related Disease of Women and Children, Ministry of Education, West China Hospital, Sichuan University, Chengdu, Sichuan 610041, P.R. China
3. Department of Evidence‑Based Medicine and Clinical Epidemiology, West China Hospital, Sichuan University, Chengdu, Sichuan 610041, P.R. China