Affiliation: | a Department of Obstetrics and Gynecology, University of North Carolina School of Medicine, Chapel Hill, NC b Department of Epidemiology, School of Public Health, University of North Carolina, Chapel Hill, NC c Department of Biostatistics, School of Public Health, University of North Carolina, Chapel Hill, NC d Carolina Population Center, University of North Carolina, Chapel Hill, NC e Department of Epidemiology, Mailman School of Public Health, Columbia University, New York, NY |