1. Department of Epidemiology and Biostatistics, School of Public Health, Guangxi Medical University, Nanning, China
2. School of Public Health, University of Hong Kong, Hong Kong, China
3. Ultrasound Diagnosis Department, Hubei Maternal and Child Health Hospital, Wuhan, China
4. Department of Maternal and Child Health, School of Public Health, Sun Yat-Sen University, Guangzhou, China
5. Department of Gynaecology and Obstetrics, Zhongnan Hospital of Wuhan University, Wuhan, China
6. Department of Epidemiology and Biostatistics, School of Health Sciences , Wuhan University, Wuhan, China