1. Section for Epidemiology, Department of Public Health,
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, Shanghai, China; and
3. Department of Epidemiology, Fielding School of Public Health, University of California, Los Angeles, California
4. Department of Obstetrics and Gynecology, Institute of Clinical Medicine,
5. National Centre for Register-Based Research, and
6. CIRRAU–Centre for Integrated Register-based Research, Aarhus University, Aarhus, Denmark;