Affiliation: | (1) Perinatal Epidemiology Research Unit, Department of Obstetrics & Gynaecology, Dalhousie University and the IWK Health Centre, Halifax, Canada;(2) Perinatal Epidemiology Research Unit, Department of Pediatrics, Dalhousie University and the IWK Health Centre, Halifax, Canada;(3) Maternal and Infant Health Section, Health Surveillance and Epidemiology Division, Public Health Agency of Canada, Ottawa, Canada |