1. Department of Epidemiology, Biostatistics, and Occupational Health; McGill University; Montreal QC Canada
2. Department of Economics; McGill University; Montreal QC Canada
3. Department of Obstetrics and Gynecology; Jewish General Hospital; McGill University; Montreal QC Canada
4. Centre for Clinical Epidemiology and Community Studies; Jewish General Hospital; Montreal QC Canada
5. Department of Obstetrics and Gynaecology; University of British Columbia; Vancouver BC Canada