Li Zhen1, Yan-Dong Yang2, Yu-Juan Li3, Li-Li Xu1, Dong-Zhi Li1. 1. Prenatal Diagnostic Center, Guangzhou Women and Children's Medical Center, Guangzhou Medical University, Guangzhou, China. 2. Department of Ultrasound, The Sixth Affiliated Hospital of Sun Yat-sen University, Guangzhou, China. 3. Prenatal Diagnosis Unit, Dongguan Maternal and Children's Healthcare Hospital, Dongguan, China.