1. Department of Ultrasonic Medicine, The First Affiliated Hospital of Sun Yat-sen University, Guangzhou, Guangdong, China;
2. Prenatal Diagnostic Center, Guangzhou Women and Children’s Medical Center affiliated to Guangzhou Medical University, Guangzhou, Guangdong, China;
3. Fetal Medicine Division, Shenzhen Luohu People’s Hospital, Shenzhen, Guangdong, China