1. Section for Epidemiology, Department of Public Health, Aarhus University, Denmark
2. Department of Epidemiology and Social Science on Reproductive Health, Shanghai Institute of Planned Parenthood Research, WHO Collaborating Center for Research in Human Reproduction, National Population & Family Planning Key Laboratory of Contraceptive Drugs and Devices, China
3. Section for Biostatistics, Department of Public Health, Aarhus University, Denmark
4. Department of Epidemiology, Fielding School of Public Health, University of California, USA