1. Department of Special Examination, Maternal and Child Health Hospital of Chun’an County, Hangzhou, Zhejiang, China
2. Department of Ultrasound, Sanmen People’s Hospital, Taizhou, Zhejiang, China
3. Department of Ultrasound, Pingyi County Hospital of Traditional Chinese Medicine, Linyi, Shandong, China
4. Department of Ultrasound, Chongqing Public Health Medical Center, Chongqing, Shandong, China