1. Institute for Preventive Medicine and Public Health, Hanoi Medical University, No.1 Ton That Tung Street, Khuong Thuong, Dong Da, Hanoi, Vietnam
2. Department of Anthropology, University of Copenhagen, Øster Farimagsgade 5, DK-1353 Copenhagen K, Denmark
3. Department of Obstetrics and Gynecology, Odense University Hospital, 5000 Odense C, Denmark
4. Department of Clinical Research, University of Southern Denmark, 5230 Odense M, Denmark
5. Department of Public Health, Faculty of Health Sciences, University of Copenhagen, Øster Farimagsgade 5, DK-1014 Copenhagen, Denmark