1. Department of Surgery, Faculty of Medicine, Ramathibodi Hospital, Mahidol University, Bangkok, Thailand
2. Section for Clinical Epidemiology and Biostatistics, Faculty of Medicine, Ramathibodi Hospital, Mahidol University, Bangkok, Thailand
3. Bureau of Reproductive Health, Department of Health, Ministry of Public Health, Nonthaburi, Thailand
4. Centre for Clinical Epidemiology and Biostatistics, Newcastle University, Newcastle, New South Wales, Australia