1. Department of Epidemiology, Joseph L. Mailman School of Public Health, Columbia University, New York, NY, USA
2. Division of Intramural Population Health Research, Eunice Kennedy Shriver National Institute of Child Health and Human Development, Rockville, MD, USA
3. Department of Obstetrics and Gynaecology and the School of Population and Public Health, University of British Columbia, and the Children’s and Women’s Hospital of British Columbia, Vancouver, British Columbia, Canada
4. School of Public Health, Boston University, Boston, MA, USA
5. Department of Obstetrics and Gynecology, College of Physicians and Surgeons, Columbia University, New York, NY, USA