1. Department of Obstetrics, Shanghai First Maternity and Infant Hospital, Tongji University School of Medicine, Shanghai 201204, China
2. Shanghai Key Laboratory of Maternal Medicine, Shanghai First Maternity and Infant Hospital, Tongji University School of Medicine, Shanghai 201204, China
3. Department of Ultrasound, Shanghai First Maternity and Infant Hospital, Tongji University school of Medicine, Shanghai 201204, China