Affiliation: | 1. Slone Epidemiology Center, Boston University, Boston, MA;2. Department of Orthopaedic Surgery, Boston Children's Hospital, Boston, MA;3. North Carolina Birth Defects Monitoring Program, State Center for Health Statistics, Raleigh, NC;4. Massachusetts Birth Defects Monitoring Program, Massachusetts Department of Public Health, Center for Birth Defects Research and Prevention, Boston, MA;5. Congenital Malformations Registry, New York State Department of Health, Albany, NY |