1. *Division of Epidemiology, University of Minnesota School of Medicine, Minneapolis, Minnesota
2. ‡National Center for Education in Maternal and Child Health, Georgetown University, Arlington, Virginia
3. §Maternal and Child Health Bureau, Health Resources and Services Administration, Department of Health and Human Services, Rockville, Maryland
4. ‖Trowbridge & Associates, Inc, Decatur, Georgia
5. ¶St Louis University School of Medicine, St Louis, Missouri