1. Department of Obstetrics and Gynecology, Wake Forest University Health Sciences, Winston-Salem, North Carolina, USA.
2. Department of Epidemiology, University of North Carolina at Chapel Hill Gillings School of Global Public Health, Chapel Hill, North Carolina, USA.
3. Carolina Population Center, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, USA.
4. University of North Carolina at Chapel Hill School of Medicine, Chapel Hill, North Carolina, USA.
5. University of North Carolina at Chapel Hill Lineberger Cancer Research Center, Chapel Hill, North Carolina, USA.