1. National Center for Birth Defect Monitoring, West China Second University Hospital, Sichuan University; Chengdu Sichuan China
2. West China School of Public Health, Sichuan University; Chengdu Sichuan China
3. Laboratory of Molecular Epidemiology for Birth Defects, West China Second University Hospital, Sichuan University; Chengdu Sichuan China
4. Department of Ultrasound; Xijing Hospital, Fourth Military Medical University; Xi'an Shanxi China
5. Department of Ultrasound; Shenzhen Maternity and Child Healthcare Hospital; Shenzhen Guangdong China
6. Department of Ultrasound; Maternal and Child Healthcare Hospital of Guangxi Zhuang Autonomous Region; Nanning Guangxi China
7. Department of Obstetrics & Gynecology; Fujian Provincial Maternal and Child Healthcare Hospital; Fuzhou Fujian China
8. Department of Ultrasound; Hubei Provincial Maternal and Child Healthcare Hospital; Wuhan Hubei China
9. Department of Ultrasound; Sichuan Provincial Maternal and Child Healthcare Hospital; Chengdu Sichuan China