1. National Center for Birth Defect Monitoring, West China Second University Hospital, Sichuan University, Chengdu, PR China;
2. Key Laboratory of Obstetric & Gynecologic and Pediatric Diseases and Birth Defects, Ministry of Education, West China Second University Hospital, Sichuan University, Chengdu, PR China;
3. State Key Laboratory of Biotherapy/Collaborative Innovation Center of Biotherapy, West China Hospital, Sichuan University, Chengdu, PR China;
4. Department of Ultrasound, Maternal and Child Healthcare Hospital of Guangxi Zhuang Autonomous Region, Nanning, PR China;
5. Department of Ultrasound, Harbin Red cross Central Hospital, Harbin, PR China;
6. Department of Ultrasound, Sichuan Provincial Maternal and Child Healthcare Hospital, Chengdu, PR China