1. School of Public Health, Department of Maternal and Child Health, University of Alabama at Birmingham, USA,
2. National Center for Health Statistics, Centers for Disease Control and Prevention, US Department of Health and Human Services, USA,
3. School of Public Health, Division of Epidemiology, University of Minnesota, USA,
4. School of Public Health, Maternal and Child Health Program, University of Hawaii, USA,
5. Medicine, Department of Obstetrics and Gynecology, University of Alabama at Birmingham, USA