1. Department of Epidemiology; Boston University School of Public Health; Boston MA
2. National Institute of Health and Welfare (THL) Helsinki, Finland
3. NHV Nordic School of Public Health; Gothenburg Sweden
4. Department of Obstetrics and Gynecology; Helsinki University Central Hospital; University of Helsinki; Helsinki Finland
5. Department of Obstetrics and Gynecology; College of Physicians and Surgeons, Columbia University, New York, NY
6. Department of Epidemiology; Mailman School of Public Health; Columbia University; New York NY