1. Section of Epidemiology and Biostatistics, Department of Obstetrics, Gynecology and Reproductive Sciences, University of Medicine and Dentistry of New Jersey, Robert Wood Johnson Medical School, New Brunswick, New Jersey, USA
2. Perinatal Epidemiology Research Unit, Departments of Obstetrics and Gynecology, and of Pediatrics, Dalhousie University, Halifax, Nova Scotia, Canada
3. Division of Maternal–Fetal Medicine, Department of Obstetrics, Gynecology and Reproductive Sciences, University of Medicine and Dentistry of New Jersey, Robert Wood Johnson Medical School, New Brunswick, New Jersey, USA