1. Department of Epidemiology, Gillings Global School of Public Health, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina.
2. Department of Obstetrics and Gynecology, School of Medicine, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina.
3. Department of Maternal and Child Health, Gillings Global School of Public Health, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina.
4. Department of Pathology and Laboratory Medicine, School of Medicine, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina.
5. Lineberger Comprehensive Cancer Center, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina.