1. Foshan Fetal Medicine Research Institute, Foshan Women and Children Hospital, Foshan, Guangdong, China
2. Department of Obstetrics, Foshan Women and Children Hospital, Foshan, Guangdong, China
3. The Second School of Clinical Medicine, Southern Medical University, Guangzhou, Guangdong, China
4. Department of Library, Foshan Women and Children Hospital, Foshan, Guangdong, China
5. Department of Library, First Affiliated Hospital, College of Medicine, Zhejiang University, Hangzhou, Zhejiang, China
6. Department of Epidemiology and Biostatistics, School of Public Health, Anhui Medical University, Hefei, Anhui, China