[1
]
Division of Reproductive Health, Centers for Disease Control and Prevention, Atlanta,
Georgia; ayn9@cdc.gov.
[2
]
Department of Pediatrics, Yale School of Medicine, New Haven, Connecticut;
[3
]
Pregnancy and Perinatology Branch, Eunice Kennedy Shriver National Institute of Child
Health and Human Development, Bethesda, Maryland;
[4
]
Data Coordinating Center, Boston University School of Public Health, Boston, Massachusetts;
and.
[5
]
Division of Reproductive Health, Centers for Disease Control and Prevention, Atlanta,
Georgia;
[6
]
Department of Pediatrics, Boston University School of Medicine, and Slone Epidemiology
Center, Boston University, Boston, Massachusetts.