1. Division of Reproductive Health, National Center for Chronic Disease Prevention and Health Promotion, Centers for Disease Control and Prevention, Atlanta, Georgia, USA.
2. Commissioned Corps of the U.S. Public Health Service, U.S. Department of Health and Human Services, Washington, DC, USA.
3. Department of Pediatrics, Harvard Medical School, Harvard University and Mount Auburn Hospital, Cambridge, Massachusetts, USA.
4. National Center on Birth Defects and Developmental Disabilities, Centers for Disease Control and Prevention, Atlanta, Georgia, USA.