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. Department of Library, Foshan Women and Children Hospital, Foshan, Guangdong, China
4. Department of Library, the First Affiliated Hospital, College of Medicine, Zhejiang University, Hangzhou, Zhejiang, China
5. Department of Epidemiology and Biostatistics, School of Public Health, Anhui Medical University, Hefei, Anhui, China